{"id":31671,"date":"2023-06-11T10:55:13","date_gmt":"2023-06-11T08:55:13","guid":{"rendered":"https:\/\/yuboost.com\/quels-sont-les-effets-indesirables-de-la-vitamine-b\/"},"modified":"2026-09-29T17:16:11","modified_gmt":"2026-09-29T15:16:11","slug":"what-are-the-side-effects-of-vitamin-b","status":"publish","type":"post","link":"https:\/\/yuboost.com\/en\/expertise\/what-are-the-side-effects-of-vitamin-b\/","title":{"rendered":"What are the side effects of vitamin B?"},"content":{"rendered":"<div>\n<div class=\"yb-art\">\n<div class=\"yb-art-container\">\n<nav class=\"yb-art-crumb\"><a href=\"\/en\/\">Home<\/a> \u203a <a href=\"https:\/\/yuboost.com\/en\/our-articles\/\">Our articles<\/a> \u203a <span>Vitamin B side effects<\/span><\/nav>\n<div class=\"yb-art-hero\">\n<div class=\"yb-art-hero-blob\"><\/div>\n<div class=\"yb-art-hero-in\">\n        <span class=\"yb-art-eyebrow\">Vitamins &amp; safety<\/span><\/p>\n<h1>Vitamin B <span class=\"yb-art-accent\">side effects<\/span> and overdose risks<\/h1>\n<p class=\"yb-art-hero-sub\">B complex, B1 to B12: which side effects are real, at what doses, and which ones are myths. A vitamin-by-vitamin review, with the safety limits set by the European Food Safety Authority.<\/p>\n<div class=\"yb-art-meta\">\n          <img decoding=\"async\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\" alt=\"Dr Alexandra Miles\"><br \/>\n          <span>By <strong>Dr Alexandra Miles<\/strong><\/span><br \/>\n          <span>\u2022<\/span><span>Reviewed September 2026<\/span><br \/>\n          <span>\u2022<\/span><span>10 min read<\/span>\n        <\/div>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"yb-art-layout\">\n<div class=\"yb-art-body\">\n<p>Vitamin B is not one vitamin but a family of eight: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B8 (biotin), B9 (folate) and B12 (cobalamin). All of them are water-soluble, which has earned them a reputation as &#8220;risk-free&#8221; vitamins: whatever the body does not need is supposed to leave in the urine. That is true for most of them at dietary doses. It is false for at least two, vitamin B6 and niacin, as soon as you move to high-dose supplements. Here is what the data show, and what should make you see a doctor.<\/p>\n<div class=\"yb-art-key\">\n<div class=\"yb-art-key-t\">Key takeaways<\/div>\n<p><strong>Vitamin B side effects<\/strong> almost always depend on the dose and on the specific vitamin. From food alone, no overdose has been described. With supplements, two vitamins call for real caution: <strong>B6<\/strong>, which can cause a neuropathy (tingling, numbness in the feet and hands) when taken for months at more than a few dozen milligrams a day, and <strong>niacin (B3)<\/strong>, responsible for hot flushes and, at very high doses, liver damage. <strong>Biotin (B8)<\/strong> will not make you ill but distorts certain blood tests. The rest of the B group, including B12, is very well tolerated. Before you supplement, a <a href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/\">vitamin and mineral check-up<\/a> measures your B6, B9 and B12 levels <strong>at home, without a prescription<\/strong>.<\/p>\n<\/p><\/div>\n<h2>The 8 B vitamins: daily needs and the limits not to exceed<\/h2>\n<p>Two figures matter for each B vitamin. The <strong>recommended daily intake<\/strong>, which covers the needs of a healthy adult. And the <strong>tolerable upper intake level<\/strong> (UL), set by the European Food Safety Authority (EFSA): the total daily dose, food and supplements combined, above which a risk of adverse effects can no longer be ruled out. For several B vitamins, EFSA was unable to set a limit, because no data showed a harmful effect. That does not mean the dose is unlimited, only that no toxicity threshold has been observed.<\/p>\n<div class=\"yb-art-tablewrap\">\n<table class=\"yb-art-table\">\n<thead>\n<tr>\n<th>Vitamin<\/th>\n<th>Recommended adult intake (women \/ men)<\/th>\n<th>EFSA upper limit (adults)<\/th>\n<th>At high doses<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td><strong>B1<\/strong> thiamine<\/td>\n<td>1.1 \/ 1.2 mg<\/td>\n<td>Not set (insufficient data)<\/td>\n<td>No documented toxicity<\/td>\n<\/tr>\n<tr>\n<td><strong>B2<\/strong> riboflavin<\/td>\n<td>1.1 \/ 1.3 mg<\/td>\n<td>Not set<\/td>\n<td>Bright yellow urine, harmless<\/td>\n<\/tr>\n<tr>\n<td><strong>B3<\/strong> niacin<\/td>\n<td>14 \/ 16 mg NE<\/td>\n<td>10 mg (nicotinic acid) \u00b7 900 mg (nicotinamide)<\/td>\n<td>Flushing, liver, blood sugar<\/td>\n<\/tr>\n<tr>\n<td><strong>B5<\/strong> pantothenic acid<\/td>\n<td>5 \/ 6 mg (adequate intake)<\/td>\n<td>Not set<\/td>\n<td>Toxicity extremely rare<\/td>\n<\/tr>\n<tr>\n<td><strong>B6<\/strong> pyridoxine<\/td>\n<td>1.3 \/ 1.3 mg<\/td>\n<td><strong>12 mg<\/strong><\/td>\n<td>Sensory neuropathy<\/td>\n<\/tr>\n<tr>\n<td><strong>B8<\/strong> biotin<\/td>\n<td>40 \u00b5g (adequate intake)<\/td>\n<td>Not set<\/td>\n<td>Distorts certain blood tests<\/td>\n<\/tr>\n<tr>\n<td><strong>B9<\/strong> folate<\/td>\n<td>400 \u00b5g<\/td>\n<td><strong>1,000 \u00b5g<\/strong> (folic acid)<\/td>\n<td>Can mask a B12 deficiency<\/td>\n<\/tr>\n<tr>\n<td><strong>B12<\/strong> cobalamin<\/td>\n<td>2.4 \u00b5g<\/td>\n<td>No defined adverse effects<\/td>\n<td>Very well tolerated<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/div>\n<p class=\"yb-art-sources\">Recommended intakes: MSD Manual, &#8220;Overview of Vitamins&#8221; (adults aged 19 to 70); B5 and B8: ANSES. Upper limits: EFSA, 2024 summary of tolerable upper intake levels. The Swiss reference values are published by the <a href=\"https:\/\/www.sge-ssn.ch\/fr\/recommandations\/nutriments-aliments\/valeurs-de-reference\/\" target=\"_blank\" rel=\"nofollow noopener\">Swiss Society for Nutrition<\/a> and the Federal Food Safety and Veterinary Office.<\/p>\n<h2>Can you overdose on vitamin B?<\/h2>\n<p>From food alone, no. The amounts found in meat, eggs, legumes, whole grains or dairy products stay far below the safety thresholds, and the body clears excess water-soluble vitamins through the kidneys.<\/p>\n<p>Supplements are another matter. A <strong>vitamin B complex<\/strong> sold in pharmacies or online can contain 20 to 100 times the daily intake of each vitamin, sometimes more. The Belgian Centre for Pharmacotherapeutic Information (CBIP) notes, for example, that one tablet of Befact Forte contains <strong>250 mg of vitamin B6<\/strong>, with an authorised dosage of up to three tablets a day and no treatment duration specified. EFSA, meanwhile, puts the safety limit for B6 at 12 mg a day. <strong>Too much vitamin B<\/strong> is therefore not a theoretical scenario: a high-dose product taken for several months is enough. The question is not &#8220;is vitamin B dangerous?&#8221;, but &#8220;which one, at what dose, for how long?&#8221;.<\/p>\n<h2>Vitamin B side effects, vitamin by vitamin<\/h2>\n<h3>Vitamin B1 (thiamine): no known oral toxicity<\/h3>\n<p>Thiamine is probably the safest B vitamin. EFSA found no data allowing it to set an upper limit, and the MSD Manual describes no toxicity syndrome. The <strong>vitamin B1 side effects<\/strong> regularly cited online, such as a drop or a rise in blood pressure, are not supported by solid data. If you take a B complex and your blood pressure fluctuates, look for another cause with your doctor rather than blaming thiamine.<\/p>\n<h3>Vitamin B2 (riboflavin): bright yellow urine, and that is all<\/h3>\n<p>Riboflavin turns urine bright yellow a few hours after intake. It is a sign that the excess is being eliminated, not a warning signal. EFSA has set no upper limit and the MSD Manual records no toxicity. Supplements of 400 mg a day are sometimes used in migraine prevention: at that dose, the urine colour is the only effect regularly reported.<\/p>\n<h3>Vitamin B3 (niacin): flushing, liver and blood sugar<\/h3>\n<p>This is the B vitamin whose <strong>adverse effects<\/strong> are best documented. According to the MSD Manual, the most common is the vasomotor flush: redness of the face and upper body, a feeling of heat, itching, within the hour after taking it. It is made worse by alcohol, exercise, sun exposure and spicy food. At higher doses, the MSD Manual describes jaundice, abdominal discomfort, visual disturbances, worsening of hyperglycaemia and the triggering of an attack in people with gout. Liver damage is more frequent with certain sustained-release preparations, and serious complications occur from roughly 3,000 mg a day.<\/p>\n<p>Niacin exists in two forms, and EFSA gives them very different limits: <strong>10 mg a day for nicotinic acid<\/strong>, which causes the flush, versus <strong>900 mg for nicotinamide<\/strong>, which does not. On a supplement label, the form used appears in the ingredient list: that is the line to read if you go red after taking it.<\/p>\n<h3>Vitamin B5 (pantothenic acid): no documented problem<\/h3>\n<p>Deficiency and toxicity are both described as &#8220;extremely rare&#8221; by the MSD Manual. EFSA has set no upper limit. Loose stools or diarrhoea are occasionally reported with doses of several grams a day, far above what a standard B complex contains.<\/p>\n<h3>Vitamin B6 (pyridoxine): the real concern in the B group<\/h3>\n<p><strong>Vitamin B6<\/strong> is the case that justifies this article. Its chronic toxicity is established and its mechanism is known: with prolonged excessive intake, the liver&#8217;s capacity to process pyridoxine is exceeded, and the free forms that accumulate become toxic to the peripheral nerves. The result is a <strong>sensory neuropathy<\/strong>. The MSD Manual describes it as a &#8220;stocking-glove&#8221; loss of sensation, with progressive sensory ataxia and severe impairment of position and vibration sense: the person no longer feels clearly where their feet are, walks less steadily, and feels tingling, numbness, burning or pins and needles in the extremities.<\/p>\n<p>Three figures to remember:<\/p>\n<ul>\n<li><strong>EFSA lowered the safety limit for B6 to 12 mg a day in 2023<\/strong> for adults, including pregnant and breastfeeding women, based on a reference point of 50 mg a day above which neuropathies have been reported;<\/li>\n<li>The Dutch pharmacovigilance centre Lareb analysed <strong>139 reports<\/strong> linked to prolonged B6 use: <strong>90 involved peripheral neuropathies<\/strong>, at doses ranging from 50 mg a day to several grams, over periods of several months to several years;<\/li>\n<li>The MSD Manual cites megadoses above 500 mg a day for the clear-cut cases, with <strong>slow and sometimes incomplete recovery<\/strong> after stopping.<\/li>\n<\/ul>\n<p>Two traps make this overdose hard to spot. First, the symptoms of too much B6 resemble those of a B6 deficiency, as the CBIP points out: faced with tingling, the temptation is to increase the dose. Second, B6 is present in a multitude of products that do not present themselves as B6 supplements: B complexes, multivitamins, products for sleep or premenstrual syndrome, energy drinks. The doses add up without anyone noticing. The only treatment is to stop taking vitamin B6, and a blood test can confirm the excess.<\/p>\n<div class=\"yb-art-quote\">\n<p>I regularly see patients who have been taking 100 mg of B6 a day for a year &#8220;for energy&#8221; and who come in with tingling in their feet. Nobody told them the safety limit was 12 mg. Vitamin B is not dangerous; badly dosed B6 is.<\/p>\n<p>          <cite>Dr Alexandra Miles, YuBoost<\/cite>\n        <\/div>\n<h3>Vitamin B8 (biotin): harmless for you, not for your blood tests<\/h3>\n<p>Biotin, found in most &#8220;hair, skin and nails&#8221; supplements, has no known toxicity and EFSA has set no limit. Its adverse effect lies elsewhere: it <strong>interferes with certain laboratory assay techniques<\/strong>. The French medicines agency (ANSM) issued a warning in March 2023 about falsely high or falsely low results for <strong>TSH, T3, T4 and thyroglobulin<\/strong>, leading to wrong diagnoses of hypothyroidism or hyperthyroidism. The US FDA has documented the same phenomenon with <strong>troponin<\/strong>, the marker used to diagnose a heart attack, with at least one reported death linked to a distorted result.<\/p>\n<p>In practice: if you take biotin, say so before any blood test, especially if it includes thyroid markers, as in the <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">complete medical check-up<\/a>. The laboratory or the doctor will tell you how long to stop it, depending on the dose you take. At YuBoost, the nurse asks you the question during the home blood draw.<\/p>\n<h3>Vitamin B9 (folic acid): an excess can mask a B12 deficiency<\/h3>\n<p>Dietary folate poses no problem. Synthetic folic acid, however, has an EFSA limit of <strong>1,000 \u00b5g a day<\/strong>, confirmed in 2023. The critical effect is not direct toxicity: at high doses, folic acid corrects the anaemia of a <a href=\"https:\/\/yuboost.com\/en\/vitamins\/vitamins-b12\/\">vitamin B12 deficiency<\/a> without correcting the nerve damage, which then keeps progressing with no warning sign in the blood count. That is why nobody should take high-dose folic acid without knowing their B12 level, especially after 60, on a vegan diet, or on long-term metformin or antacids.<\/p>\n<h3>Vitamin B12 (cobalamin): very well tolerated<\/h3>\n<p>EFSA has identified <strong>no defined adverse effects<\/strong> for B12, even at high doses, and has therefore set no limit. The reported effects remain rare and mild: an acne flare at very high doses, an exceptional allergic reaction, pinkish urine. We cover them in a dedicated article: <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-are-the-side-effects-of-vitamin-b12\/\">the side effects of vitamin B12<\/a>. The real issue with B12 is almost always deficiency, not excess. A high blood level without supplementation, on the other hand, deserves a medical opinion, because it can point to another condition.<\/p>\n<h2>Vitamin B12 and high blood pressure: what the data say<\/h2>\n<p>This is one of the most frequently asked questions about the effects of vitamin B, and the honest answer is: <strong>nothing shows that vitamin B12 raises blood pressure<\/strong>. A Japanese cross-sectional study published in 2020 in <em>Scientific Reports<\/em>, involving 2,079 adults, measured homocysteine, folate and plasma B12 in relation to hypertension. The authors conclude that there is no clear association between B12 levels and hypertension. A trend was seen in women in the highest quartile, but it did not reach statistical significance and was not found in men.<\/p>\n<p>Other observational studies point the other way and suggest that a good B-vitamin status could be associated with lower blood pressure, through homocysteine metabolism. None of these studies allows a causal conclusion in either direction. What can be said with certainty: if your blood pressure is high, B12 is not the most likely cause, and hypertension needs its own work-up. YuBoost&#8217;s <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">complete blood check-up<\/a> measures kidney function, lipids and blood sugar, among others, which matter far more in this context.<\/p>\n<h2>Vitamin B complex: the side effects people actually feel<\/h2>\n<p>B complexes (Becozym, Vit B Denk, Befact, B-50, B-100 and their equivalents) combine the eight vitamins at doses that vary widely from one brand to another. The effects reported by users do not always match the effects that have been demonstrated. Here is how to read them.<\/p>\n<ul>\n<li><strong>Digestive upset<\/strong> (nausea, abdominal discomfort, loose stools): common with high-dose products, especially on an empty stomach. Niacin contributes to it. It goes away when you stop, or when you take the supplement in the middle of a meal.<\/li>\n<li><strong>Redness and warmth of the face<\/strong>: that is the nicotinic acid flush. Check the form of niacin and its dose.<\/li>\n<li><strong>Disturbed sleep<\/strong>: often searched for (&#8220;vitamin B complex and sleep&#8221;), little studied. Some people report trouble falling asleep or more vivid dreams with B6 or B12 taken in the evening. The evidence is anecdotal, the fix is simple: take the complex in the morning.<\/li>\n<li><strong>Tingling, numbness<\/strong>: take it seriously. This is the warning sign of B6 neuropathy. Stop the product and have your B6 measured.<\/li>\n<li><strong>Weight gain<\/strong>: nothing supports it. B vitamins provide no calories. A rise in blood sugar is described with high-dose niacin, but that is not weight gain.<\/li>\n<li><strong>Allergic reactions<\/strong> (hives, itching, swelling of the face): rare, possible with any component, including excipients. They require stopping the product and prompt medical advice in case of swelling or difficulty breathing.<\/li>\n<\/ul>\n<p>The practical rule fits in one sentence: <strong>compare the &#8220;B6&#8221; line and the &#8220;niacin&#8221; line on the label with the EFSA limits<\/strong> (12 mg and 10 mg of nicotinic acid). If the product exceeds them several times over, it is not designed for daily long-term use without supervision. To find out whether a B complex is even useful in your case, read <a href=\"https:\/\/yuboost.com\/en\/expertise\/in-what-cases-should-vitamin-b-be-taken\/\">in what cases vitamin B should be taken<\/a>.<\/p>\n<h2>Too much vitamin B: which symptoms should alert you?<\/h2>\n<p>If you take a B-vitamin supplement and recognise yourself in any of these signs, do not increase the dose, and see a doctor:<\/p>\n<ul>\n<li>Tingling, numbness or burning in the feet and hands, a feeling of walking on cotton wool, unsteadiness when walking with your eyes closed;<\/li>\n<li>Repeated hot flushes and redness after each dose;<\/li>\n<li>Jaundice, dark urine, pain under the right ribs (warning signs for the liver);<\/li>\n<li>A gout attack in someone prone to it;<\/li>\n<li>Swelling of the face or lips, difficulty breathing (emergency).<\/li>\n<\/ul>\n<p>Conversely, bright yellow or pinkish urine after a B complex is not a symptom of overdose. For the risks linked to the other vitamins, in particular A and D, which are stored in the body, see <a href=\"https:\/\/yuboost.com\/en\/expertise\/what-are-the-risks-of-taking-too-many-vitamins\/\">what are the risks of taking too many vitamins<\/a>; for the combinations to avoid, <a href=\"https:\/\/yuboost.com\/en\/expertise\/which-vitamins-cant-be-taken-together\/\">which vitamins can&#8217;t be taken together<\/a>.<\/p>\n<h2>Should you test your B vitamins before supplementing?<\/h2>\n<p>Yes, as soon as you plan to take them for more than a few weeks or the product is high-dose. The logic is the same as for any treatment: you only correct what is missing. A genuine B12, B9 or B6 deficiency is treated, with defined doses and duration; &#8220;just in case&#8221; supplementation exposes you to the effects described above without any demonstrated benefit. To spot a deficiency, <a href=\"https:\/\/yuboost.com\/en\/expertise\/how-can-you-tell-if-you-have-a-vitamin-deficiency\/\">the signs of a vitamin deficiency<\/a> give you clues, but only a blood test settles the question.<\/p>\n<p>YuBoost&#8217;s <a href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/\">vitamin and mineral check-up<\/a> measures <strong>11 biomarkers<\/strong>, including <strong>vitamins B6, B9 and B12<\/strong>, vitamin D, calcium, iron, ferritin, transferrin, magnesium and zinc. How it works:<\/p>\n<ul>\n<li><strong>Blood draw at home<\/strong> by a registered nurse, <strong>no prescription needed<\/strong>, in Lausanne, Geneva, Zurich and across French-speaking Switzerland;<\/li>\n<li><strong>Analysis in an accredited Swiss laboratory<\/strong>, results within 7 working days;<\/li>\n<li><strong>Personalised medical report<\/strong> and recommendations, with an optional online consultation with a doctor.<\/li>\n<\/ul>\n<p>The vitamin and mineral check-up costs <strong>CHF 370<\/strong>. If you want a broader picture, the <a href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/\">complete medical check-up<\/a> (34 biomarkers, CHF 350) also covers the thyroid, liver, kidneys and blood sugar. When a deficiency is confirmed and the oral route is not suitable, a <a href=\"https:\/\/yuboost.com\/en\/vitamins\/group-b-vitamins\/\">vitamin B injection<\/a> or the <a href=\"https:\/\/yuboost.com\/en\/iv-therapy\/energy\/\">Energy vitamin infusion<\/a> (B-group vitamins, B12 and 750 mg of vitamin C, CHF 300) can be offered on medical indication, at home. A vitamin infusion is prescribed after a blood test, never blindly: that is exactly what this article recommends for supplements too. Vitamin B side effects are not inevitable, they are a matter of dose and duration, and the only way to avoid them is to know where you stand before you start.<\/p>\n<h2>Frequently asked questions<\/h2>\n<div class=\"yb-art-faq\">\n<details open>\n<summary>What are the side effects of vitamin B?<\/summary>\n<p>At dietary doses, none. With high-dose supplements, the documented effects are flushing and digestive upset linked to niacin (B3), sensory neuropathy linked to prolonged intake of vitamin B6 above the 12 mg daily limit set by EFSA, and rare allergic reactions. Riboflavin (B2) turns urine bright yellow, which is harmless.<\/p>\n<\/details>\n<details>\n<summary>Is vitamin B dangerous?<\/summary>\n<p>Not as a group. Two vitamins call for caution in supplement form: B6, whose prolonged excess can damage the peripheral nerves with sometimes incomplete recovery, and niacin in the form of nicotinic acid, which can harm the liver at very high doses. The other six have no known toxicity according to EFSA and the MSD Manual.<\/p>\n<\/details>\n<details>\n<summary>What is the maximum dose of vitamin B6 per day?<\/summary>\n<p>In 2023, EFSA set the tolerable upper intake level at 12 mg a day for adults, food and supplements combined. Neuropathies have been reported from 50 mg a day taken for several months. Many B complexes exceed this threshold: read the label.<\/p>\n<\/details>\n<details>\n<summary>Does vitamin B12 raise blood pressure?<\/summary>\n<p>No data show that. A study published in 2020 in <em>Scientific Reports<\/em> in more than 2,000 adults found no clear association between blood B12 levels and hypertension. If your blood pressure is high, it needs its own work-up, regardless of B12.<\/p>\n<\/details>\n<details>\n<summary>Does vitamin B complex keep you awake?<\/summary>\n<p>Some people report trouble falling asleep or vivid dreams with a B complex taken in the evening, mainly because of B6 and B12. The effect is little studied and does not occur in everyone. Taking the supplement in the morning is usually enough to solve the problem.<\/p>\n<\/details>\n<details>\n<summary>Does vitamin B make you gain weight?<\/summary>\n<p>No. B vitamins provide no calories and no study shows weight gain linked to a B complex. High-dose niacin can disturb blood sugar, which is a different issue and concerns doses far above those in standard supplements.<\/p>\n<\/details>\n<details>\n<summary>Should I stop biotin before a blood test?<\/summary>\n<p>Often, yes. Biotin distorts certain assays, in particular TSH, T3, T4, thyroglobulin and troponin, as reported by the ANSM and the FDA. Always tell the laboratory or the nurse that you take biotin before the blood draw: the interruption period depends on the dose.<\/p>\n<\/details>\n<details>\n<summary>How do I know whether I have too much or too little vitamin B?<\/summary>\n<p>Through a blood test. YuBoost&#8217;s vitamin and mineral check-up measures vitamins B6, B9 and B12 along with eight other markers, at home and without a prescription in French-speaking Switzerland, with results interpreted by a doctor.<\/p>\n<\/details><\/div>\n<h2>Sources<\/h2>\n<p class=\"yb-art-sources\">\n          \u2022 EFSA, NDA Panel, <em>Scientific opinion on the tolerable upper intake level for vitamin B6<\/em>, EFSA Journal 2023, doi:10.2903\/j.efsa.2023.8006: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC10189633\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 EFSA, NDA Panel, <em>Scientific opinion on the tolerable upper intake level for folate<\/em>, EFSA Journal 2023, doi:10.2903\/j.efsa.2023.8353: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC10641704\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 EFSA, <em>Summary of Tolerable Upper Intake Levels<\/em>, 2024 version (niacin, B1, B2, B5, B8, B12): <a href=\"https:\/\/www.efsa.europa.eu\/sites\/default\/files\/2024-05\/ul-summary-report.pdf\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 MSD Manual Professional Edition, <em>Vitamin B6 Toxicity<\/em>: <a href=\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-b6-toxicity\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 MSD Manual Professional Edition, <em>Niacin Toxicity<\/em>: <a href=\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/niacin-toxicity\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 MSD Manual Professional Edition, <em>Overview of Vitamins<\/em> (recommended intakes, deficiency and toxicity): <a href=\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/overview-of-vitamins\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 CBIP, Folia Pharmacotherapeutica, October 2024, <em>Attention aux neuropathies li\u00e9es \u00e0 l&#8217;utilisation prolong\u00e9e de doses (trop) \u00e9lev\u00e9es de vitamine B6<\/em> (in French): <a href=\"https:\/\/www.cbip.be\/fr\/articles\/4417\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 ANSM, safety information of 13 March 2023, <em>Interf\u00e9rence de la biotine avec les analyses de laboratoire de la fonction thyro\u00efdienne<\/em> (in French): <a href=\"https:\/\/ansm.sante.fr\/informations-de-securite\/interference-de-la-biotine-avec-les-analyses-de-laboratoire-de-la-fonction-thyroidienne\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 FDA, <em>Biotin interference with troponin lab tests<\/em>: <a href=\"https:\/\/www.fda.gov\/medical-devices\/in-vitro-diagnostics\/biotin-interference-troponin-lab-tests-assays-subject-biotin-interference\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Tamura T. et al., <em>Association between plasma levels of homocysteine, folate, and vitamin B12, and dietary folate intake and hypertension in a cross-sectional study<\/em>, Scientific Reports, 2020: <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC7595187\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 ANSES, <em>Dietary reference values for vitamins and minerals<\/em> (adequate intakes for vitamins B5 and B8): <a href=\"https:\/\/www.anses.fr\/en\/content\/dietary-reference-values-vitamins-and-minerals\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a><br \/>\n          \u2022 Swiss Society for Nutrition SSN, <em>Reference values for nutrient intakes<\/em>: <a href=\"https:\/\/www.sge-ssn.ch\/fr\/recommandations\/nutriments-aliments\/valeurs-de-reference\/\" target=\"_blank\" rel=\"nofollow noopener\">link<\/a>\n        <\/p>\n<\/p><\/div>\n<aside class=\"yb-art-aside\">\n<div class=\"yb-art-panel yb-art-panel--cta\">\n<div class=\"k\">Take action<\/div>\n<h3>Test your <em>B vitamins<\/em> before you supplement<\/h3>\n<p>B6, B9, B12, vitamin D, iron, magnesium and zinc in a single check-up. At home, no prescription needed, across French-speaking Switzerland.<\/p>\n<p>          <a class=\"yb-art-sbtn yb-art-sbtn--p\" href=\"https:\/\/yuboost.com\/en\/booking\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=cta-side\">Book an appointment<\/a><br \/>\n          <a class=\"yb-art-sbtn yb-art-sbtn--g\" href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=cta-side-checkup\">See the check-up: CHF 370<\/a>\n        <\/div>\n<p>        <a class=\"yb-art-panel yb-art-panel--author\" href=\"https:\/\/yuboost.com\/en\/about-us\/\"><br \/>\n          <img decoding=\"async\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\" alt=\"Dr Alexandra Miles\"><\/p>\n<div><strong>Dr Alexandra Miles<\/strong><span>CEO YuBoost \u00b7 Functional medicine<\/span><\/div>\n<p>        <\/a><br \/>\n      <\/aside>\n<\/p><\/div>\n<\/p><\/div>\n<div class=\"yb-rel\">\n<div class=\"yb-rel__head\">\n      <span class=\"yb-art-eyebrow\">Go further<\/span><\/p>\n<h2>Measure before you supplement<\/h2>\n<p>At home across French-speaking Switzerland, no prescription needed.<\/p>\n<\/p><\/div>\n<div class=\"yb-rel__viewport\">\n      <button type=\"button\" class=\"yb-rel__nav yb-rel__nav--prev\" aria-label=\"Previous\"><svg viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" aria-hidden=\"true\"><path d=\"M15 18l-6-6 6-6\"\/><\/svg><\/button><\/p>\n<div class=\"yb-rel__track-wrap\">\n<div class=\"yb-rel__track\">\n<p>          <a class=\"yb-rel__card yb-rel__card--featured\" href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=rel-vitamins\"><br \/>\n            <span class=\"yb-rel__badge yb-rel__badge--top\">Most relevant<\/span><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/06\/Bilan-vitamines.png\" alt=\"Vitamin and mineral check-up with vitamin B6, B9 and B12 testing at home in Switzerland\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Deficiencies<\/p>\n<h3 class=\"yb-rel__name\">Vitamin &amp; mineral check-up<\/h3>\n<p class=\"yb-rel__desc\">Vitamins B6, B9, B12 and D, iron, ferritin, transferrin, magnesium, calcium, zinc. At home.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">B6 \u00b7 B9 \u00b7 B12<\/span><span class=\"yb-rel__chip\">11 markers<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 370<\/span><span class=\"yb-rel__cta\">Book<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=rel-checkup\"><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/04\/bilan-sanguin-complet.png\" alt=\"Complete medical check-up at home in Switzerland, 34 biomarkers\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Complete check-up<\/p>\n<h3 class=\"yb-rel__name\">Complete medical check-up<\/h3>\n<p class=\"yb-rel__desc\">34 biomarkers: thyroid, blood sugar, liver, kidneys, lipids, inflammation.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">Complete<\/span><span class=\"yb-rel__chip\">Blood test<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 350<\/span><span class=\"yb-rel__cta\">Book<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/iv-therapy\/energy\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=rel-energy\"><br \/>\n            <span class=\"yb-rel__badge yb-rel__badge--new\">On medical indication<\/span><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/03\/Energy.png\" alt=\"Energy vitamin infusion with B-group vitamins at home in Switzerland\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Vitamin infusion<\/p>\n<h3 class=\"yb-rel__name\">Energy<\/h3>\n<p class=\"yb-rel__desc\">B-group vitamins, B12 and 750 mg of vitamin C. After a blood test and medical advice, at home.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">B vitamins<\/span><span class=\"yb-rel__chip\">60 min<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">CHF 300<\/span><span class=\"yb-rel__cta\">Discover<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p>\n<p>          <a class=\"yb-rel__card\" href=\"https:\/\/yuboost.com\/en\/vitamins\/group-b-vitamins\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=rel-injection-b\"><br \/>\n            <img decoding=\"async\" class=\"yb-rel__img\" src=\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/04\/EN-Vitamin-B-complex-e1776841777472.png\" alt=\"Vitamin B injection at home in Switzerland\" loading=\"lazy\"><\/p>\n<div class=\"yb-rel__cbody\">\n<p class=\"yb-rel__cat\">Vitamin B<\/p>\n<h3 class=\"yb-rel__name\">Vitamin B injection<\/h3>\n<p class=\"yb-rel__desc\">The complete guide to the B group: roles, needs, deficiency and routes of administration.<\/p>\n<div class=\"yb-rel__chips\"><span class=\"yb-rel__chip\">Guide<\/span><span class=\"yb-rel__chip\">At home<\/span><\/div>\n<div class=\"yb-rel__footer\"><span class=\"yb-rel__price\">Discover<\/span><span class=\"yb-rel__cta\">View<\/span><\/div>\n<\/p><\/div>\n<p>          <\/a><\/p><\/div>\n<\/p><\/div>\n<p>      <button type=\"button\" class=\"yb-rel__nav yb-rel__nav--next\" aria-label=\"Next\"><svg viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\" aria-hidden=\"true\"><path d=\"M9 18l6-6-6-6\"\/><\/svg><\/button>\n    <\/div>\n<div class=\"yb-rel__dots\"><\/div>\n<\/p><\/div>\n<div class=\"yb-art-container\">\n<div class=\"yb-art-cta\">\n<div class=\"yb-art-cta-blob\"><\/div>\n<div class=\"yb-art-cta-in\">\n        <span class=\"yb-art-eyebrow\">Take action<\/span><\/p>\n<h2>Test before you <span class=\"yb-art-accent\">supplement<\/span><\/h2>\n<p class=\"yb-art-cta-sub\">Vitamins B6, B9, B12, vitamin D, iron, magnesium and zinc in a single check-up, at home across French-speaking Switzerland and without a prescription. Blood draw by a registered nurse, results interpreted by a doctor.<\/p>\n<p>        <a class=\"yb-art-btn\" href=\"https:\/\/yuboost.com\/en\/booking\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=cta-final\">Book an appointment<\/a><br \/>\n        <a class=\"yb-art-btn-ghost\" href=\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&#038;utm_medium=article&#038;utm_campaign=vitamin-b-side-effects&#038;utm_content=cta-final-checkup\">See the check-up: CHF 370<\/a>\n      <\/div>\n<\/p><\/div>\n<p class=\"yb-art-disc\">This article is for information only and does not replace individual medical advice. In case of persistent tingling, jaundice or an allergic reaction after taking a supplement, consult a healthcare professional. Reviewed by Dr Alexandra Miles, September 2026.<\/p>\n<\/p><\/div>\n<\/div>\n<\/div>\n<p><!--more--><br \/>\n<!-- {\"type\":\"layout\",\"children\":[{\"type\":\"section\",\"props\":{\"image_position\":\"center-center\",\"style\":\"default\",\"title_breakpoint\":\"xl\",\"title_position\":\"top-left\",\"title_rotation\":\"left\",\"vertical_align\":\"\",\"width\":\"large\"},\"children\":[{\"type\":\"row\",\"children\":[{\"type\":\"column\",\"props\":{\"image_position\":\"center-center\",\"position_sticky_breakpoint\":\"m\"},\"children\":[{\"type\":\"html\",\"props\":{\"content\":\"\n\n<div class=\\\"yb-art\\\">\\n\\n  \n\n<div class=\\\"yb-art-container\\\">\\n\\n    \n\n<nav class=\\\"yb-art-crumb\\\"><a href=\\\"\/en\/\\\">Home<\/a> \u203a <a href=\\\"\/en\/our-articles\/\\\">Our articles<\/a> \u203a <span>Vitamin B side effects<\/span><\/nav>\n\n\\n\\n    \n\n<div class=\\\"yb-art-hero\\\">\\n      \n\n<div class=\\\"yb-art-hero-blob\\\"><\/div>\n\n\\n      \n\n<div class=\\\"yb-art-hero-in\\\">\\n        <span class=\\\"yb-art-eyebrow\\\">Vitamins &amp; safety<\/span>\\n        \n\n<h1>Vitamin B <span class=\\\"yb-art-accent\\\">side effects<\/span> and overdose risks<\/h1>\n\n\\n        \n\n<p class=\\\"yb-art-hero-sub\\\">B complex, B1 to B12: which side effects are real, at what doses, and which ones are myths. A vitamin-by-vitamin review, with the safety limits set by the European Food Safety Authority.<\/p>\n\n\\n        \n\n<div class=\\\"yb-art-meta\\\">\\n          <img src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\\\" alt=\\\"Dr Alexandra Miles\\\">\\n          <span>By <strong>Dr Alexandra Miles<\/strong><\/span>\\n          <span>\u2022<\/span><span>Reviewed September 2026<\/span>\\n          <span>\u2022<\/span><span>10 min read<\/span>\\n        <\/div>\n\n\\n      <\/div>\n\n\\n    <\/div>\n\n\\n\\n    \n\n<div class=\\\"yb-art-layout\\\">\\n\\n      \n\n<div class=\\\"yb-art-body\\\">\\n\\n        \n\n<p>Vitamin B is not one vitamin but a family of eight: B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B8 (biotin), B9 (folate) and B12 (cobalamin). All of them are water-soluble, which has earned them a reputation as \\\"risk-free\\\" vitamins: whatever the body does not need is supposed to leave in the urine. That is true for most of them at dietary doses. It is false for at least two, vitamin B6 and niacin, as soon as you move to high-dose supplements. Here is what the data show, and what should make you see a doctor.<\/p>\n\n\\n\\n        \n\n<div class=\\\"yb-art-key\\\">\\n          \n\n<div class=\\\"yb-art-key-t\\\">Key takeaways<\/div>\n\n\\n          \n\n<p><strong>Vitamin B side effects<\/strong> almost always depend on the dose and on the specific vitamin. From food alone, no overdose has been described. With supplements, two vitamins call for real caution: <strong>B6<\/strong>, which can cause a neuropathy (tingling, numbness in the feet and hands) when taken for months at more than a few dozen milligrams a day, and <strong>niacin (B3)<\/strong>, responsible for hot flushes and, at very high doses, liver damage. <strong>Biotin (B8)<\/strong> will not make you ill but distorts certain blood tests. The rest of the B group, including B12, is very well tolerated. Before you supplement, a <a href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/\\\">vitamin and mineral check-up<\/a> measures your B6, B9 and B12 levels <strong>at home, without a prescription<\/strong>.<\/p>\n\n\\n        <\/div>\n\n\\n\\n        \n\n<h2>The 8 B vitamins: daily needs and the limits not to exceed<\/h2>\n\n\\n        \n\n<p>Two figures matter for each B vitamin. The <strong>recommended daily intake<\/strong>, which covers the needs of a healthy adult. And the <strong>tolerable upper intake level<\/strong> (UL), set by the European Food Safety Authority (EFSA): the total daily dose, food and supplements combined, above which a risk of adverse effects can no longer be ruled out. For several B vitamins, EFSA was unable to set a limit, because no data showed a harmful effect. That does not mean the dose is unlimited, only that no toxicity threshold has been observed.<\/p>\n\n\\n        \n\n<div class=\\\"yb-art-tablewrap\\\">\\n          \n\n<table class=\\\"yb-art-table\\\">\\n            \n\n<thead>\n\n<tr>\n\n<th>Vitamin<\/th>\n\n\n\n<th>Recommended adult intake (women \/ men)<\/th>\n\n\n\n<th>EFSA upper limit (adults)<\/th>\n\n\n\n<th>At high doses<\/th>\n\n<\/tr>\n\n<\/thead>\n\n\\n            \n\n<tbody>\\n              \n\n<tr>\n\n<td><strong>B1<\/strong> thiamine<\/td>\n\n\n\n<td>1.1 \/ 1.2 mg<\/td>\n\n\n\n<td>Not set (insufficient data)<\/td>\n\n\n\n<td>No documented toxicity<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B2<\/strong> riboflavin<\/td>\n\n\n\n<td>1.1 \/ 1.3 mg<\/td>\n\n\n\n<td>Not set<\/td>\n\n\n\n<td>Bright yellow urine, harmless<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B3<\/strong> niacin<\/td>\n\n\n\n<td>14 \/ 16 mg NE<\/td>\n\n\n\n<td>10 mg (nicotinic acid) \u00b7 900 mg (nicotinamide)<\/td>\n\n\n\n<td>Flushing, liver, blood sugar<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B5<\/strong> pantothenic acid<\/td>\n\n\n\n<td>5 \/ 6 mg (adequate intake)<\/td>\n\n\n\n<td>Not set<\/td>\n\n\n\n<td>Toxicity extremely rare<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B6<\/strong> pyridoxine<\/td>\n\n\n\n<td>1.3 \/ 1.3 mg<\/td>\n\n\n\n<td><strong>12 mg<\/strong><\/td>\n\n\n\n<td>Sensory neuropathy<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B8<\/strong> biotin<\/td>\n\n\n\n<td>40 \u00b5g (adequate intake)<\/td>\n\n\n\n<td>Not set<\/td>\n\n\n\n<td>Distorts certain blood tests<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B9<\/strong> folate<\/td>\n\n\n\n<td>400 \u00b5g<\/td>\n\n\n\n<td><strong>1,000 \u00b5g<\/strong> (folic acid)<\/td>\n\n\n\n<td>Can mask a B12 deficiency<\/td>\n\n<\/tr>\n\n\\n              \n\n<tr>\n\n<td><strong>B12<\/strong> cobalamin<\/td>\n\n\n\n<td>2.4 \u00b5g<\/td>\n\n\n\n<td>No defined adverse effects<\/td>\n\n\n\n<td>Very well tolerated<\/td>\n\n<\/tr>\n\n\\n            <\/tbody>\n\n\\n          <\/table>\n\n\\n        <\/div>\n\n\\n        \n\n<p class=\\\"yb-art-sources\\\">Recommended intakes: MSD Manual, \\\"Overview of Vitamins\\\" (adults aged 19 to 70); B5 and B8: ANSES. Upper limits: EFSA, 2024 summary of tolerable upper intake levels. The Swiss reference values are published by the <a href=\\\"https:\/\/www.sge-ssn.ch\/fr\/recommandations\/nutriments-aliments\/valeurs-de-reference\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">Swiss Society for Nutrition<\/a> and the Federal Food Safety and Veterinary Office.<\/p>\n\n\\n\\n        \n\n<h2>Can you overdose on vitamin B?<\/h2>\n\n\\n        \n\n<p>From food alone, no. The amounts found in meat, eggs, legumes, whole grains or dairy products stay far below the safety thresholds, and the body clears excess water-soluble vitamins through the kidneys.<\/p>\n\n\\n        \n\n<p>Supplements are another matter. A <strong>vitamin B complex<\/strong> sold in pharmacies or online can contain 20 to 100 times the daily intake of each vitamin, sometimes more. The Belgian Centre for Pharmacotherapeutic Information (CBIP) notes, for example, that one tablet of Befact Forte contains <strong>250 mg of vitamin B6<\/strong>, with an authorised dosage of up to three tablets a day and no treatment duration specified. EFSA, meanwhile, puts the safety limit for B6 at 12 mg a day. <strong>Too much vitamin B<\/strong> is therefore not a theoretical scenario: a high-dose product taken for several months is enough. The question is not \\\"is vitamin B dangerous?\\\", but \\\"which one, at what dose, for how long?\\\".<\/p>\n\n\\n\\n        \n\n<h2>Vitamin B side effects, vitamin by vitamin<\/h2>\n\n\\n\\n        \n\n<h3>Vitamin B1 (thiamine): no known oral toxicity<\/h3>\n\n\\n        \n\n<p>Thiamine is probably the safest B vitamin. EFSA found no data allowing it to set an upper limit, and the MSD Manual describes no toxicity syndrome. The <strong>vitamin B1 side effects<\/strong> regularly cited online, such as a drop or a rise in blood pressure, are not supported by solid data. If you take a B complex and your blood pressure fluctuates, look for another cause with your doctor rather than blaming thiamine.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B2 (riboflavin): bright yellow urine, and that is all<\/h3>\n\n\\n        \n\n<p>Riboflavin turns urine bright yellow a few hours after intake. It is a sign that the excess is being eliminated, not a warning signal. EFSA has set no upper limit and the MSD Manual records no toxicity. Supplements of 400 mg a day are sometimes used in migraine prevention: at that dose, the urine colour is the only effect regularly reported.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B3 (niacin): flushing, liver and blood sugar<\/h3>\n\n\\n        \n\n<p>This is the B vitamin whose <strong>adverse effects<\/strong> are best documented. According to the MSD Manual, the most common is the vasomotor flush: redness of the face and upper body, a feeling of heat, itching, within the hour after taking it. It is made worse by alcohol, exercise, sun exposure and spicy food. At higher doses, the MSD Manual describes jaundice, abdominal discomfort, visual disturbances, worsening of hyperglycaemia and the triggering of an attack in people with gout. Liver damage is more frequent with certain sustained-release preparations, and serious complications occur from roughly 3,000 mg a day.<\/p>\n\n\\n        \n\n<p>Niacin exists in two forms, and EFSA gives them very different limits: <strong>10 mg a day for nicotinic acid<\/strong>, which causes the flush, versus <strong>900 mg for nicotinamide<\/strong>, which does not. On a supplement label, the form used appears in the ingredient list: that is the line to read if you go red after taking it.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B5 (pantothenic acid): no documented problem<\/h3>\n\n\\n        \n\n<p>Deficiency and toxicity are both described as \\\"extremely rare\\\" by the MSD Manual. EFSA has set no upper limit. Loose stools or diarrhoea are occasionally reported with doses of several grams a day, far above what a standard B complex contains.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B6 (pyridoxine): the real concern in the B group<\/h3>\n\n\\n        \n\n<p><strong>Vitamin B6<\/strong> is the case that justifies this article. Its chronic toxicity is established and its mechanism is known: with prolonged excessive intake, the liver's capacity to process pyridoxine is exceeded, and the free forms that accumulate become toxic to the peripheral nerves. The result is a <strong>sensory neuropathy<\/strong>. The MSD Manual describes it as a \\\"stocking-glove\\\" loss of sensation, with progressive sensory ataxia and severe impairment of position and vibration sense: the person no longer feels clearly where their feet are, walks less steadily, and feels tingling, numbness, burning or pins and needles in the extremities.<\/p>\n\n\\n        \n\n<p>Three figures to remember:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li><strong>EFSA lowered the safety limit for B6 to 12 mg a day in 2023<\/strong> for adults, including pregnant and breastfeeding women, based on a reference point of 50 mg a day above which neuropathies have been reported;<\/li>\n\n\\n          \n\n<li>The Dutch pharmacovigilance centre Lareb analysed <strong>139 reports<\/strong> linked to prolonged B6 use: <strong>90 involved peripheral neuropathies<\/strong>, at doses ranging from 50 mg a day to several grams, over periods of several months to several years;<\/li>\n\n\\n          \n\n<li>The MSD Manual cites megadoses above 500 mg a day for the clear-cut cases, with <strong>slow and sometimes incomplete recovery<\/strong> after stopping.<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>Two traps make this overdose hard to spot. First, the symptoms of too much B6 resemble those of a B6 deficiency, as the CBIP points out: faced with tingling, the temptation is to increase the dose. Second, B6 is present in a multitude of products that do not present themselves as B6 supplements: B complexes, multivitamins, products for sleep or premenstrual syndrome, energy drinks. The doses add up without anyone noticing. The only treatment is to stop taking vitamin B6, and a blood test can confirm the excess.<\/p>\n\n\\n\\n        \n\n<div class=\\\"yb-art-quote\\\">\\n          \n\n<p>I regularly see patients who have been taking 100 mg of B6 a day for a year \\\"for energy\\\" and who come in with tingling in their feet. Nobody told them the safety limit was 12 mg. Vitamin B is not dangerous; badly dosed B6 is.<\/p>\n\n\\n          <cite>Dr Alexandra Miles, YuBoost<\/cite>\\n        <\/div>\n\n\\n\\n        \n\n<h3>Vitamin B8 (biotin): harmless for you, not for your blood tests<\/h3>\n\n\\n        \n\n<p>Biotin, found in most \\\"hair, skin and nails\\\" supplements, has no known toxicity and EFSA has set no limit. Its adverse effect lies elsewhere: it <strong>interferes with certain laboratory assay techniques<\/strong>. The French medicines agency (ANSM) issued a warning in March 2023 about falsely high or falsely low results for <strong>TSH, T3, T4 and thyroglobulin<\/strong>, leading to wrong diagnoses of hypothyroidism or hyperthyroidism. The US FDA has documented the same phenomenon with <strong>troponin<\/strong>, the marker used to diagnose a heart attack, with at least one reported death linked to a distorted result.<\/p>\n\n\\n        \n\n<p>In practice: if you take biotin, say so before any blood test, especially if it includes thyroid markers, as in the <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">complete medical check-up<\/a>. The laboratory or the doctor will tell you how long to stop it, depending on the dose you take. At YuBoost, the nurse asks you the question during the home blood draw.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B9 (folic acid): an excess can mask a B12 deficiency<\/h3>\n\n\\n        \n\n<p>Dietary folate poses no problem. Synthetic folic acid, however, has an EFSA limit of <strong>1,000 \u00b5g a day<\/strong>, confirmed in 2023. The critical effect is not direct toxicity: at high doses, folic acid corrects the anaemia of a <a href=\\\"\/en\/vitamins\/vitamins-b12\/\\\">vitamin B12 deficiency<\/a> without correcting the nerve damage, which then keeps progressing with no warning sign in the blood count. That is why nobody should take high-dose folic acid without knowing their B12 level, especially after 60, on a vegan diet, or on long-term metformin or antacids.<\/p>\n\n\\n\\n        \n\n<h3>Vitamin B12 (cobalamin): very well tolerated<\/h3>\n\n\\n        \n\n<p>EFSA has identified <strong>no defined adverse effects<\/strong> for B12, even at high doses, and has therefore set no limit. The reported effects remain rare and mild: an acne flare at very high doses, an exceptional allergic reaction, pinkish urine. We cover them in a dedicated article: <a href=\\\"\/en\/expertise\/what-are-the-side-effects-of-vitamin-b12\/\\\">the side effects of vitamin B12<\/a>. The real issue with B12 is almost always deficiency, not excess. A high blood level without supplementation, on the other hand, deserves a medical opinion, because it can point to another condition.<\/p>\n\n\\n\\n        \n\n<h2>Vitamin B12 and high blood pressure: what the data say<\/h2>\n\n\\n        \n\n<p>This is one of the most frequently asked questions about the effects of vitamin B, and the honest answer is: <strong>nothing shows that vitamin B12 raises blood pressure<\/strong>. A Japanese cross-sectional study published in 2020 in <em>Scientific Reports<\/em>, involving 2,079 adults, measured homocysteine, folate and plasma B12 in relation to hypertension. The authors conclude that there is no clear association between B12 levels and hypertension. A trend was seen in women in the highest quartile, but it did not reach statistical significance and was not found in men.<\/p>\n\n\\n        \n\n<p>Other observational studies point the other way and suggest that a good B-vitamin status could be associated with lower blood pressure, through homocysteine metabolism. None of these studies allows a causal conclusion in either direction. What can be said with certainty: if your blood pressure is high, B12 is not the most likely cause, and hypertension needs its own work-up. YuBoost's <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">complete blood check-up<\/a> measures kidney function, lipids and blood sugar, among others, which matter far more in this context.<\/p>\n\n\\n\\n        \n\n<h2>Vitamin B complex: the side effects people actually feel<\/h2>\n\n\\n        \n\n<p>B complexes (Becozym, Vit B Denk, Befact, B-50, B-100 and their equivalents) combine the eight vitamins at doses that vary widely from one brand to another. The effects reported by users do not always match the effects that have been demonstrated. Here is how to read them.<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li><strong>Digestive upset<\/strong> (nausea, abdominal discomfort, loose stools): common with high-dose products, especially on an empty stomach. Niacin contributes to it. It goes away when you stop, or when you take the supplement in the middle of a meal.<\/li>\n\n\\n          \n\n<li><strong>Redness and warmth of the face<\/strong>: that is the nicotinic acid flush. Check the form of niacin and its dose.<\/li>\n\n\\n          \n\n<li><strong>Disturbed sleep<\/strong>: often searched for (\\\"vitamin B complex and sleep\\\"), little studied. Some people report trouble falling asleep or more vivid dreams with B6 or B12 taken in the evening. The evidence is anecdotal, the fix is simple: take the complex in the morning.<\/li>\n\n\\n          \n\n<li><strong>Tingling, numbness<\/strong>: take it seriously. This is the warning sign of B6 neuropathy. Stop the product and have your B6 measured.<\/li>\n\n\\n          \n\n<li><strong>Weight gain<\/strong>: nothing supports it. B vitamins provide no calories. A rise in blood sugar is described with high-dose niacin, but that is not weight gain.<\/li>\n\n\\n          \n\n<li><strong>Allergic reactions<\/strong> (hives, itching, swelling of the face): rare, possible with any component, including excipients. They require stopping the product and prompt medical advice in case of swelling or difficulty breathing.<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>The practical rule fits in one sentence: <strong>compare the \\\"B6\\\" line and the \\\"niacin\\\" line on the label with the EFSA limits<\/strong> (12 mg and 10 mg of nicotinic acid). If the product exceeds them several times over, it is not designed for daily long-term use without supervision. To find out whether a B complex is even useful in your case, read <a href=\\\"\/en\/expertise\/in-what-cases-should-vitamin-b-be-taken\/\\\">in what cases vitamin B should be taken<\/a>.<\/p>\n\n\\n\\n        \n\n<h2>Too much vitamin B: which symptoms should alert you?<\/h2>\n\n\\n        \n\n<p>If you take a B-vitamin supplement and recognise yourself in any of these signs, do not increase the dose, and see a doctor:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li>Tingling, numbness or burning in the feet and hands, a feeling of walking on cotton wool, unsteadiness when walking with your eyes closed;<\/li>\n\n\\n          \n\n<li>Repeated hot flushes and redness after each dose;<\/li>\n\n\\n          \n\n<li>Jaundice, dark urine, pain under the right ribs (warning signs for the liver);<\/li>\n\n\\n          \n\n<li>A gout attack in someone prone to it;<\/li>\n\n\\n          \n\n<li>Swelling of the face or lips, difficulty breathing (emergency).<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>Conversely, bright yellow or pinkish urine after a B complex is not a symptom of overdose. For the risks linked to the other vitamins, in particular A and D, which are stored in the body, see <a href=\\\"\/en\/expertise\/what-are-the-risks-of-taking-too-many-vitamins\/\\\">what are the risks of taking too many vitamins<\/a>; for the combinations to avoid, <a href=\\\"\/en\/expertise\/which-vitamins-cant-be-taken-together\/\\\">which vitamins can't be taken together<\/a>.<\/p>\n\n\\n\\n        \n\n<h2>Should you test your B vitamins before supplementing?<\/h2>\n\n\\n        \n\n<p>Yes, as soon as you plan to take them for more than a few weeks or the product is high-dose. The logic is the same as for any treatment: you only correct what is missing. A genuine B12, B9 or B6 deficiency is treated, with defined doses and duration; \\\"just in case\\\" supplementation exposes you to the effects described above without any demonstrated benefit. To spot a deficiency, <a href=\\\"\/en\/expertise\/how-can-you-tell-if-you-have-a-vitamin-deficiency\/\\\">the signs of a vitamin deficiency<\/a> give you clues, but only a blood test settles the question.<\/p>\n\n\\n        \n\n<p>YuBoost's <a href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/\\\">vitamin and mineral check-up<\/a> measures <strong>11 biomarkers<\/strong>, including <strong>vitamins B6, B9 and B12<\/strong>, vitamin D, calcium, iron, ferritin, transferrin, magnesium and zinc. How it works:<\/p>\n\n\\n        \n\n<ul>\\n          \n\n<li><strong>Blood draw at home<\/strong> by a registered nurse, <strong>no prescription needed<\/strong>, in Lausanne, Geneva, Zurich and across French-speaking Switzerland;<\/li>\n\n\\n          \n\n<li><strong>Analysis in an accredited Swiss laboratory<\/strong>, results within 7 working days;<\/li>\n\n\\n          \n\n<li><strong>Personalised medical report<\/strong> and recommendations, with an optional online consultation with a doctor.<\/li>\n\n\\n        <\/ul>\n\n\\n        \n\n<p>The vitamin and mineral check-up costs <strong>CHF 370<\/strong>. If you want a broader picture, the <a href=\\\"\/en\/check-up\/medical-check-up\/\\\">complete medical check-up<\/a> (34 biomarkers, CHF 350) also covers the thyroid, liver, kidneys and blood sugar. When a deficiency is confirmed and the oral route is not suitable, a <a href=\\\"\/en\/vitamins\/group-b-vitamins\/\\\">vitamin B injection<\/a> or the <a href=\\\"\/en\/iv-therapy\/energy\/\\\">Energy vitamin infusion<\/a> (B-group vitamins, B12 and 750 mg of vitamin C, CHF 300) can be offered on medical indication, at home. A vitamin infusion is prescribed after a blood test, never blindly: that is exactly what this article recommends for supplements too. Vitamin B side effects are not inevitable, they are a matter of dose and duration, and the only way to avoid them is to know where you stand before you start.<\/p>\n\n\\n\\n        \n\n<h2>Frequently asked questions<\/h2>\n\n\\n        \n\n<div class=\\\"yb-art-faq\\\">\\n          \n\n<details open>\n\n<summary>What are the side effects of vitamin B?<\/summary>\n\n\n\n<p>At dietary doses, none. With high-dose supplements, the documented effects are flushing and digestive upset linked to niacin (B3), sensory neuropathy linked to prolonged intake of vitamin B6 above the 12 mg daily limit set by EFSA, and rare allergic reactions. Riboflavin (B2) turns urine bright yellow, which is harmless.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Is vitamin B dangerous?<\/summary>\n\n\n\n<p>Not as a group. Two vitamins call for caution in supplement form: B6, whose prolonged excess can damage the peripheral nerves with sometimes incomplete recovery, and niacin in the form of nicotinic acid, which can harm the liver at very high doses. The other six have no known toxicity according to EFSA and the MSD Manual.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>What is the maximum dose of vitamin B6 per day?<\/summary>\n\n\n\n<p>In 2023, EFSA set the tolerable upper intake level at 12 mg a day for adults, food and supplements combined. Neuropathies have been reported from 50 mg a day taken for several months. Many B complexes exceed this threshold: read the label.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Does vitamin B12 raise blood pressure?<\/summary>\n\n\n\n<p>No data show that. A study published in 2020 in <em>Scientific Reports<\/em> in more than 2,000 adults found no clear association between blood B12 levels and hypertension. If your blood pressure is high, it needs its own work-up, regardless of B12.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Does vitamin B complex keep you awake?<\/summary>\n\n\n\n<p>Some people report trouble falling asleep or vivid dreams with a B complex taken in the evening, mainly because of B6 and B12. The effect is little studied and does not occur in everyone. Taking the supplement in the morning is usually enough to solve the problem.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Does vitamin B make you gain weight?<\/summary>\n\n\n\n<p>No. B vitamins provide no calories and no study shows weight gain linked to a B complex. High-dose niacin can disturb blood sugar, which is a different issue and concerns doses far above those in standard supplements.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>Should I stop biotin before a blood test?<\/summary>\n\n\n\n<p>Often, yes. Biotin distorts certain assays, in particular TSH, T3, T4, thyroglobulin and troponin, as reported by the ANSM and the FDA. Always tell the laboratory or the nurse that you take biotin before the blood draw: the interruption period depends on the dose.<\/p>\n\n<\/details>\n\n\\n          \n\n<details>\n\n<summary>How do I know whether I have too much or too little vitamin B?<\/summary>\n\n\n\n<p>Through a blood test. YuBoost's vitamin and mineral check-up measures vitamins B6, B9 and B12 along with eight other markers, at home and without a prescription in French-speaking Switzerland, with results interpreted by a doctor.<\/p>\n\n<\/details>\n\n\\n        <\/div>\n\n\\n\\n        \n\n<h2>Sources<\/h2>\n\n\\n        \n\n<p class=\\\"yb-art-sources\\\">\\n          \u2022 EFSA, NDA Panel, <em>Scientific opinion on the tolerable upper intake level for vitamin B6<\/em>, EFSA Journal 2023, doi:10.2903\/j.efsa.2023.8006: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC10189633\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 EFSA, NDA Panel, <em>Scientific opinion on the tolerable upper intake level for folate<\/em>, EFSA Journal 2023, doi:10.2903\/j.efsa.2023.8353: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC10641704\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 EFSA, <em>Summary of Tolerable Upper Intake Levels<\/em>, 2024 version (niacin, B1, B2, B5, B8, B12): <a href=\\\"https:\/\/www.efsa.europa.eu\/sites\/default\/files\/2024-05\/ul-summary-report.pdf\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 MSD Manual Professional Edition, <em>Vitamin B6 Toxicity<\/em>: <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/vitamin-b6-toxicity\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 MSD Manual Professional Edition, <em>Niacin Toxicity<\/em>: <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/niacin-toxicity\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 MSD Manual Professional Edition, <em>Overview of Vitamins<\/em> (recommended intakes, deficiency and toxicity): <a href=\\\"https:\/\/www.msdmanuals.com\/professional\/nutritional-disorders\/vitamin-deficiency-dependency-and-toxicity\/overview-of-vitamins\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 CBIP, Folia Pharmacotherapeutica, October 2024, <em>Attention aux neuropathies li\u00e9es \u00e0 l'utilisation prolong\u00e9e de doses (trop) \u00e9lev\u00e9es de vitamine B6<\/em> (in French): <a href=\\\"https:\/\/www.cbip.be\/fr\/articles\/4417\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 ANSM, safety information of 13 March 2023, <em>Interf\u00e9rence de la biotine avec les analyses de laboratoire de la fonction thyro\u00efdienne<\/em> (in French): <a href=\\\"https:\/\/ansm.sante.fr\/informations-de-securite\/interference-de-la-biotine-avec-les-analyses-de-laboratoire-de-la-fonction-thyroidienne\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 FDA, <em>Biotin interference with troponin lab tests<\/em>: <a href=\\\"https:\/\/www.fda.gov\/medical-devices\/in-vitro-diagnostics\/biotin-interference-troponin-lab-tests-assays-subject-biotin-interference\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Tamura T. et al., <em>Association between plasma levels of homocysteine, folate, and vitamin B12, and dietary folate intake and hypertension in a cross-sectional study<\/em>, Scientific Reports, 2020: <a href=\\\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC7595187\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 ANSES, <em>Dietary reference values for vitamins and minerals<\/em> (adequate intakes for vitamins B5 and B8): <a href=\\\"https:\/\/www.anses.fr\/en\/content\/dietary-reference-values-vitamins-and-minerals\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a><br \/>\\n          \u2022 Swiss Society for Nutrition SSN, <em>Reference values for nutrient intakes<\/em>: <a href=\\\"https:\/\/www.sge-ssn.ch\/fr\/recommandations\/nutriments-aliments\/valeurs-de-reference\/\\\" target=\\\"_blank\\\" rel=\\\"nofollow noopener\\\">link<\/a>\\n        <\/p>\n\n\\n\\n      <\/div>\n\n\\n\\n      \n\n<aside class=\\\"yb-art-aside\\\">\\n        \n\n<div class=\\\"yb-art-panel yb-art-panel--cta\\\">\\n          \n\n<div class=\\\"k\\\">Take action<\/div>\n\n\\n          \n\n<h3>Test your <em>B vitamins<\/em> before you supplement<\/h3>\n\n\\n          \n\n<p>B6, B9, B12, vitamin D, iron, magnesium and zinc in a single check-up. At home, no prescription needed, across French-speaking Switzerland.<\/p>\n\n\\n          <a class=\\\"yb-art-sbtn yb-art-sbtn--p\\\" href=\\\"\/en\/booking\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=cta-side\\\">Book an appointment<\/a>\\n          <a class=\\\"yb-art-sbtn yb-art-sbtn--g\\\" href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=cta-side-checkup\\\">See the check-up: CHF 370<\/a>\\n        <\/div>\n\n\\n        <a class=\\\"yb-art-panel yb-art-panel--author\\\" href=\\\"\/en\/about-us\/\\\">\\n          <img src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/01\/Dr.-alexandra-miles-fmh.png\\\" alt=\\\"Dr Alexandra Miles\\\">\\n          \n\n<div><strong>Dr Alexandra Miles<\/strong><span>CEO YuBoost \u00b7 Functional medicine<\/span><\/div>\n\n\\n        <\/a>\\n      <\/aside>\n\n\\n\\n    <\/div>\n\n\\n  <\/div>\n\n\\n\\n  \n\n<div class=\\\"yb-rel\\\">\\n    \n\n<div class=\\\"yb-rel__head\\\">\\n      <span class=\\\"yb-art-eyebrow\\\">Go further<\/span>\\n      \n\n<h2>Measure before you supplement<\/h2>\n\n\\n      \n\n<p>At home across French-speaking Switzerland, no prescription needed.<\/p>\n\n\\n    <\/div>\n\n\\n    \n\n<div class=\\\"yb-rel__viewport\\\">\\n      <button type=\\\"button\\\" class=\\\"yb-rel__nav yb-rel__nav--prev\\\" aria-label=\\\"Previous\\\"><svg viewBox=\\\"0 0 24 24\\\" fill=\\\"none\\\" stroke=\\\"currentColor\\\" stroke-width=\\\"2\\\" aria-hidden=\\\"true\\\"><path d=\\\"M15 18l-6-6 6-6\\\"\/><\/svg><\/button>\\n      \n\n<div class=\\\"yb-rel__track-wrap\\\">\\n        \n\n<div class=\\\"yb-rel__track\\\">\\n\\n          <a class=\\\"yb-rel__card yb-rel__card--featured\\\" href=\\\"https:\/\/yuboost.com\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=rel-vitamins\\\">\\n            <span class=\\\"yb-rel__badge yb-rel__badge--top\\\">Most relevant<\/span>\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/06\/Bilan-vitamines.png\\\" alt=\\\"Vitamin and mineral check-up with vitamin B6, B9 and B12 testing at home in Switzerland\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Deficiencies<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Vitamin &amp; mineral check-up<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">Vitamins B6, B9, B12 and D, iron, ferritin, transferrin, magnesium, calcium, zinc. At home.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">B6 \u00b7 B9 \u00b7 B12<\/span><span class=\\\"yb-rel__chip\\\">11 markers<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 370<\/span><span class=\\\"yb-rel__cta\\\">Book<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/check-up\/medical-check-up\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=rel-checkup\\\">\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/04\/bilan-sanguin-complet.png\\\" alt=\\\"Complete medical check-up at home in Switzerland, 34 biomarkers\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Complete check-up<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Complete medical check-up<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">34 biomarkers: thyroid, blood sugar, liver, kidneys, lipids, inflammation.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">Complete<\/span><span class=\\\"yb-rel__chip\\\">Blood test<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 350<\/span><span class=\\\"yb-rel__cta\\\">Book<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/iv-therapy\/energy\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=rel-energy\\\">\\n            <span class=\\\"yb-rel__badge yb-rel__badge--new\\\">On medical indication<\/span>\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2025\/03\/Energy.png\\\" alt=\\\"Energy vitamin infusion with B-group vitamins at home in Switzerland\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Vitamin infusion<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Energy<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">B-group vitamins, B12 and 750 mg of vitamin C. After a blood test and medical advice, at home.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">B vitamins<\/span><span class=\\\"yb-rel__chip\\\">60 min<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">CHF 300<\/span><span class=\\\"yb-rel__cta\\\">Discover<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n          <a class=\\\"yb-rel__card\\\" href=\\\"https:\/\/yuboost.com\/en\/vitamins\/group-b-vitamins\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=rel-injection-b\\\">\\n            <img class=\\\"yb-rel__img\\\" src=\\\"https:\/\/yuboost.com\/wp-content\/uploads\/2026\/04\/EN-Vitamin-B-complex-e1776841777472.png\\\" alt=\\\"Vitamin B injection at home in Switzerland\\\" loading=\\\"lazy\\\">\\n            \n\n<div class=\\\"yb-rel__cbody\\\">\\n              \n\n<p class=\\\"yb-rel__cat\\\">Vitamin B<\/p>\n\n\\n              \n\n<h3 class=\\\"yb-rel__name\\\">Vitamin B injection<\/h3>\n\n\\n              \n\n<p class=\\\"yb-rel__desc\\\">The complete guide to the B group: roles, needs, deficiency and routes of administration.<\/p>\n\n\\n              \n\n<div class=\\\"yb-rel__chips\\\"><span class=\\\"yb-rel__chip\\\">Guide<\/span><span class=\\\"yb-rel__chip\\\">At home<\/span><\/div>\n\n\\n              \n\n<div class=\\\"yb-rel__footer\\\"><span class=\\\"yb-rel__price\\\">Discover<\/span><span class=\\\"yb-rel__cta\\\">View<\/span><\/div>\n\n\\n            <\/div>\n\n\\n          <\/a>\\n\\n        <\/div>\n\n\\n      <\/div>\n\n\\n      <button type=\\\"button\\\" class=\\\"yb-rel__nav yb-rel__nav--next\\\" aria-label=\\\"Next\\\"><svg viewBox=\\\"0 0 24 24\\\" fill=\\\"none\\\" stroke=\\\"currentColor\\\" stroke-width=\\\"2\\\" aria-hidden=\\\"true\\\"><path d=\\\"M9 18l6-6-6-6\\\"\/><\/svg><\/button>\\n    <\/div>\n\n\\n    \n\n<div class=\\\"yb-rel__dots\\\"><\/div>\n\n\\n  <\/div>\n\n\\n\\n  \n\n<div class=\\\"yb-art-container\\\">\\n    \n\n<div class=\\\"yb-art-cta\\\">\\n      \n\n<div class=\\\"yb-art-cta-blob\\\"><\/div>\n\n\\n      \n\n<div class=\\\"yb-art-cta-in\\\">\\n        <span class=\\\"yb-art-eyebrow\\\">Take action<\/span>\\n        \n\n<h2>Test before you <span class=\\\"yb-art-accent\\\">supplement<\/span><\/h2>\n\n\\n        \n\n<p class=\\\"yb-art-cta-sub\\\">Vitamins B6, B9, B12, vitamin D, iron, magnesium and zinc in a single check-up, at home across French-speaking Switzerland and without a prescription. Blood draw by a registered nurse, results interpreted by a doctor.<\/p>\n\n\\n        <a class=\\\"yb-art-btn\\\" href=\\\"\/en\/booking\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=cta-final\\\">Book an appointment<\/a>\\n        <a class=\\\"yb-art-btn-ghost\\\" href=\\\"\/en\/check-up\/vitamin-and-mineral-checkup\/?utm_source=blog&amp;utm_medium=article&amp;utm_campaign=vitamin-b-side-effects&amp;utm_content=cta-final-checkup\\\">See the check-up: CHF 370<\/a>\\n      <\/div>\n\n\\n    <\/div>\n\n\\n    \n\n<p class=\\\"yb-art-disc\\\">This article is for information only and does not replace individual medical advice. In case of persistent tingling, jaundice or an allergic reaction after taking a supplement, consult a healthcare professional. Reviewed by Dr Alexandra Miles, September 2026.<\/p>\n\n\\n  <\/div>\n\n\\n\\n<\/div>\n\n\"}}]}]}],\"name\":\"Post\"}],\"version\":\"5.0.46\",\"yooessentialsVersion\":\"3.0.15\"} --><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Home \u203a Our articles \u203a Vitamin B side effects Vitamins &amp; safety Vitamin B side effects and overdose risks B complex, B1 to B12: which side effects are real, at what doses, and which ones are myths. A vitamin-by-vitamin review, with the safety limits set by the European Food Safety Authority. By Dr Alexandra Miles [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":41792,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[80],"tags":[],"class_list":["post-31671","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-expertise"],"acf":[],"_links":{"self":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31671","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/comments?post=31671"}],"version-history":[{"count":5,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31671\/revisions"}],"predecessor-version":[{"id":41794,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/posts\/31671\/revisions\/41794"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/media\/41792"}],"wp:attachment":[{"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/media?parent=31671"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/categories?post=31671"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yuboost.com\/en\/wp-json\/wp\/v2\/tags?post=31671"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}