Vitamin B12 supplements for vegans and older adults

By the DieticiansWorldwide.com editorial team · 17 October 2026 · Supplements & industry

Who actually needs a B12 supplement

Most people who eat meat, fish, eggs or dairy get enough vitamin B12 from food. The NHS puts it plainly: if you eat those foods, "you should be able to get enough vitamin B12 from your diet" (NHS, B vitamins and folic acid). In the United States, survey data from 2017 to March 2020 found that only 5% of men and 11% of women had intakes from food and drink below the average requirement of 2 µg a day (NIH Office of Dietary Supplements).

So the question is not "should everyone take B12?" but "whose diet or digestion makes food unreliable?" Four groups stand out:

• Vegans, and vegetarians who eat little dairy or egg. B12 occurs naturally only in animal foods. Plants, including seaweed and mushrooms, are not a dependable source.
• Older adults. Stomach changes with age reduce your ability to release B12 from food.
• People taking metformin or long-term acid-reducing medicines. Both are linked with lower B12 levels.
• People who have had bariatric (weight-loss) surgery, especially gastric bypass and sleeve gastrectomy.

If you are in one of these groups, a supplement or fortified foods are usually a sensible precaution. If you already have symptoms such as pins and needles, a sore red tongue, unusual tiredness or memory problems, get tested before you start, so that you and your clinician have a clear baseline. Our guide to B12 deficiency symptoms and tests covers diagnosis in detail; this article is about choosing and using supplements well.

How much you need, and why supplement doses look so large

Daily needs are measured in micrograms (µg, also written mcg). Authorities disagree on the exact figure because they use different methods:

• the NHS says adults aged 19 to 64 need about 1.5 µg a day;
• the US Recommended Dietary Allowance is 2.4 µg for adults, 2.6 µg in pregnancy and 2.8 µg while breastfeeding, according to the NIH;
• the European Food Safety Authority set an Adequate Intake of 4 µg a day for adults in 2015, with 4.5 µg in pregnancy and 5 µg during breastfeeding (EFSA NDA Panel).

Supplement labels, by contrast, often say 500 or 1,000 µg. That is not marketing excess so much as physiology. Your body absorbs B12 mainly through a binding protein made in the stomach called intrinsic factor, and that route saturates at a dose of about 1 to 2 µg. Above that, only a small fraction passes through by simple diffusion. The NIH reports that absorption is about 50% at doses under 1 to 2 µg, "only about 2% at doses of 500 mcg and 1.3% at doses of 1,000 mcg".

The absorption percentages come from a 2016 review of B12 in vegetarians (Rizzo and colleagues, Nutrients); the last column is simple arithmetic from those figures. Two practical points follow. First, several small doses spread through the day are absorbed more efficiently than one large one, which is why fortified foods eaten at several meals work well. Second, a high-dose tablet still delivers a useful amount even when the intrinsic factor route is damaged, because the passive route does not depend on the stomach. That is the basis for high-dose oral treatment in people with absorption problems.

Product strengths vary widely. The NIH notes that multivitamins typically contain 5 to 25 µg of B12, B-complex products 50 to 500 µg, and B12-only products usually 500 to 1,000 µg. If you take more than one product, add them up before buying another.

Methylcobalamin vs cyanocobalamin: which form is best?

This is the question shoppers ask most, and the evidence gives a less exciting answer than the marketing. B12 exists in several forms. Methylcobalamin and adenosylcobalamin are the forms your cells use directly; cyanocobalamin and hydroxocobalamin are converted into them after absorption.

Cyanocobalamin is the most common form in supplements, and the NIH states that "no evidence indicates that absorption rates of vitamin B12 in supplements vary by form of the vitamin". A 2015 review of the biochemistry reached the same conclusion from a different angle: all forms are processed through the same pathway inside the cell, and the authors concluded that supplementing methylcobalamin or adenosylcobalamin "is unlikely to be advantageous" compared with cyanocobalamin (Obeid and colleagues, Molecular Nutrition and Food Research).

In the UK, NICE's March 2024 guideline tells clinicians to advise people buying over-the-counter B12 to choose a product containing cyanocobalamin, methylcobalamin or adenosylcobalamin, and to explain that "some supplements do not contain enough, or the right type, of vitamin B12 to be effective" (NICE NG239). The Vegan Society recommends cyanocobalamin because it is "the most stable, as well as economical, widely available and well researched" (The Vegan Society).

For most people, then, paying extra for an "active" form buys no proven benefit.

Delivery format matters less than you might think, too. The NIH says evidence "suggests no difference in efficacy between oral and sublingual forms". Prescription nasal gel also raises blood levels; in one small study of 10 older adults, nasal bioavailability was about 2%, similar to an oral dose. Choose the format you will actually take every day.

Vegans and vegetarians: food-first or supplement-first?

Both approaches can work. What matters is that one of them is reliable and consistent.

The food-first route

The NHS lists breakfast cereals fortified with B12, unsweetened soya drinks fortified with B12, yeast extract and fortified nutritional yeast flakes as vegan sources, while noting that "a vitamin B12 supplement may be needed" (NHS, the vegan diet). Because absorption is most efficient in small amounts, fortified foods eaten at two or three meals a day can meet needs well, but only if you check labels and eat them every day, because fortification varies between products and countries. Our free healthy eating check can help you see whether fortified foods actually feature in your week.

The supplement-first route

A daily or weekly supplement removes the guesswork. A 12-week randomised trial in 40 vegans and vegetarians with marginal B12 status compared 350 µg a week (taken as 50 µg a day) with a single 2,000 µg dose once a week, both sublingual (Del Bo' and colleagues, Clinical Nutrition, 2019). Both restored serum B12 and improved metabolic markers such as methylmalonic acid and homocysteine, with no difference between groups. The authors favoured the daily 50 µg schedule. This was a small, short trial, so treat it as reassurance that modest daily doses work rather than proof of one ideal dose.

In practice, dietitians tend to steer people towards whichever routine they will keep. If you forget daily tablets, a weekly higher dose may suit you; if you dislike pills, a carefully planned fortified-food pattern may.

Pregnancy, breastfeeding and children

This is the group where getting it wrong matters most. The NIH warns that exclusively breastfed infants of mothers who eat no animal products can develop deficiency "sometimes very early in life", with risks including neurological damage and developmental delay. If you are vegan and pregnant or breastfeeding, make B12 a non-negotiable part of your routine and discuss your intake with your midwife, GP or a dietitian. When B12 is used to treat a dietary deficiency in pregnancy or breastfeeding, NICE suggests clinicians consider at least 1 mg (1,000 µg) a day. Children on vegan diets need age-appropriate B12 too; ask a paediatric dietitian rather than splitting adult tablets.

Older adults: why food B12 becomes less reliable

Ageing does not usually change what you eat as much as what you can absorb. B12 in meat, fish and dairy is bound to protein and needs stomach acid and enzymes to release it. The NIH reports that atrophic gastritis, which reduces both acid and intrinsic factor, affects about 2% of the general population but 8% to 9% of adults aged 65 and over, and that, depending on the definition, between 3% and 43% of older adults living in the community have low B12.

Here, the food-first versus supplement-first debate has a specific answer. B12 added to fortified foods and supplements is already in free form, so it does not need stomach acid to release it. The NIH notes that people who struggle to absorb B12 from food "absorb free vitamin B12 normally". For many older adults, a fortified breakfast cereal or a modest supplement therefore works better than simply eating more meat.

The exception is autoimmune gastritis (pernicious anaemia), where intrinsic factor is missing. That needs a medical diagnosis and usually lifelong treatment managed by your GP, often by injection. NICE also suggests injections rather than tablets for dietary deficiency in some older people, for example those who are frail with several conditions, recently in hospital, or living with cognitive impairment, because reliably taking tablets can be hard.

Metformin, acid-reducing medicines and other drugs

Does metformin lower B12?

Yes, it can. In June 2022 the UK medicines regulator, the MHRA, said reduced B12 is "now considered to be a common side effect" of metformin, affecting up to 1 in 10 people who take it, with risk rising at higher doses and longer treatment (MHRA Drug Safety Update). The MHRA advises testing if symptoms suggest deficiency and considering periodic monitoring in people with other risk factors.

Do not stop metformin because of this. The NIH describes it as a first-line treatment for prediabetes and diabetes. Instead, ask your GP or diabetes team whether your B12 should be checked, especially if you also eat little animal food, are older or take acid-reducing medicine. If you are comparing metformin with supplements marketed for blood sugar, our evidence review of berberine as "nature's Ozempic" explains why that is not a like-for-like swap.

Acid-reducing medicines and others

Proton pump inhibitors such as omeprazole and lansoprazole, and H2-receptor antagonists, slow acid release and can reduce absorption of food-bound B12 over time. NICE's list of medicines that raise risk also includes colchicine, phenobarbital, pregabalin, primidone and topiramate. Our guide to supplement and medicine interactions explains how to raise these questions with your pharmacist.

After weight-loss surgery

Bariatric surgery reduces the stomach cells that make acid and intrinsic factor, and some operations bypass part of the small intestine. B12 deficiency is common afterwards. The American Society for Metabolic and Bariatric Surgery (ASMBS) 2016 micronutrient guideline reports deficiency rates under 20% after gastric bypass and 4% to 20% after sleeve gastrectomy at two to five years, and recommends that all post-surgery patients take B12 (Parrott and colleagues, ASMBS). Its suggested maintenance options are 350 to 500 µg a day by disintegrating tablet, sublingual tablet or liquid, a nasal spray as directed, or 1,000 µg a month by injection, with 1,000 µg a day to correct a deficiency.

Can tablets replace injections after surgery? A randomised trial in 50 people with low B12 after gastric bypass compared 1,000 µg of oral methylcobalamin daily with hydroxocobalamin injections every two months; B12 normalised in everyone and there was no significant difference between groups after six months (Schijns and colleagues, American Journal of Clinical Nutrition, 2018). In the UK, NICE suggests clinicians consider intramuscular rather than oral replacement for deficiency caused by malabsorption, with at least 1 mg a day if tablets are used. Follow your bariatric team's plan, and keep up the blood tests they schedule.

Is high-dose B12 safe?

For most people, yes. There is no Tolerable Upper Intake Level for B12 in the US because its potential for toxicity is low, and the NIH notes that "the body does not store excess amounts". The UK takes a more cautious line: the NHS says "taking 2mg or less a day of vitamin B12 in supplements is unlikely to cause any harm", while noting there is not enough evidence on the effects of high daily doses.

A few signals deserve honesty rather than alarm:

• Cancer associations are mixed. In one large observational study, men who took at least 55 µg a day of supplemental B12 for about 10 years had a 40% higher risk of lung cancer, with no link in women. However, a meta-analysis of 18 randomised trials with 74,498 people found B-vitamin supplements containing 20 to 2,000 µg of B12 had little or no effect on cancer incidence or deaths over two to seven years. Observational studies cannot prove cause.
• Kidney disease. In the DIVINe trial, 238 people with diabetic kidney disease took a combined tablet of folic acid 2.5 mg, vitamin B6 25 mg and B12 1 mg, or placebo. After 36 months, kidney function fell faster in the vitamin group and vascular events were twice as common (House and colleagues, JAMA, 2010). The trial tested a high-dose combination, so B12 alone cannot be blamed, but if you have kidney disease, agree any B-vitamin supplement with your renal team.
• Folic acid can hide B12 deficiency. The NHS warns that more than 1 mg of folic acid a day can mask its symptoms. If you take high-dose folic acid, make sure your B12 status has been considered.
• No proven energy boost. The NIH says B12 supplements do not improve athletic performance or endurance in people who are not deficient. Tiredness has many causes worth investigating.

Reading the label: what testing does and does not guarantee

Supplements are not licensed like medicines. In the United States, the FDA states that it "does not have the authority to approve dietary supplements before they are marketed", and manufacturers are responsible for making sure products are not adulterated or mislabelled (FDA). If you are in the US, our United States country guide shows how to find a registered dietitian there.

Independent quality seals can help. The NIH explains that these seals indicate a product "was properly manufactured, contains the ingredients listed on the label, and does not contain harmful levels of contaminants", but adds that "these seals do not guarantee that a product is safe or effective" (NIH ODS, what you need to know). In other words, a seal tells you the tablet matches its label; it cannot tell you whether you need it. Our guide to third-party tested supplements explains what the different schemes check.

When you compare B12 products, check:

1. The form: cyanocobalamin, methylcobalamin or adenosylcobalamin.
2. The amount per dose in µg, and whether a "serving" is one tablet or two.
3. Everything else in the product. B-complex products may contain high-dose B6 and folic acid. The NHS warns that 200 mg or more of B6 a day can cause loss of feeling in the arms and legs. Combination "energy" products may add caffeine.
4. Vegan status, if relevant, for capsule shells and coatings.
5. Claims. Be wary of products promising energy, weight loss or brain power.

If you take several supplements, this is a good moment to review them together. Our reviews of magnesium glycinate, vitamin D supplements and collagen supplements apply the same evidence-first test. For the wider picture of how dietitians assess products, see our supplements hub.

When to test, and when to ask a professional

Testing is worth arranging before you start a supplement if you have symptoms, are pregnant or planning pregnancy, take metformin or long-term acid-reducing medicine, have had stomach or bowel surgery, or have an autoimmune condition. Serum B12 is the usual first test, but the NIH notes that methylmalonic acid is the most sensitive marker and can confirm deficiency when serum results are borderline. If you have symptoms, arrange the test before you start a supplement.

If you are healthy and simply vegan, many dietitians are comfortable recommending a supplement without testing first, then checking status if symptoms appear or circumstances change. Keep eating a varied diet alongside it: B12 is one nutrient, and vegan diets also need planning for iodine, calcium, vitamin D and omega-3 fats. Building in plenty of high-fibre foods such as beans, lentils and whole grains is part of the same healthy pattern.

A registered dietitian can look at your diet, medicines, test results and preferences and turn them into a plan you will stick to, whether that is fortified foods, a daily tablet or a weekly dose.

Book a session with a dietitian