Vitamin B12: What It Actually Does (And What the Evidence Shows)

B12 gets marketed almost entirely as an "energy" vitamin, but that's the least interesting thing about it. Here's what a real deficiency actually looks like, who's structurally at risk regardless of how "healthy" their diet is, and how much you actually need.

Written by Vita Globe Editorial Team | Reviewed against peer-reviewed research and NIH guidance

Why Vegans and Vegetarians Are a Special Case

Most nutrient deficiencies are about eating poorly. B12 is different: it occurs naturally only in animal foods, so "people who eat little or no animal foods, such as vegetarians and vegans, might not get enough vitamin B12 from their diets" — regardless of how well-planned or nutrient-dense that diet otherwise is^[1]. This isn't a fixable-with-more-vegetables problem; it's a structural gap in plant-based eating that only fortified foods or a supplement can close.

It matters beyond the individual, too: NIH notes that strict vegetarian or vegan mothers can have babies born with insufficient B12 levels, which is why this is worth taking seriously before and during pregnancy, not just as a general wellness afterthought^[1]. If you eat a fully or mostly plant-based diet, a regular B12 source isn't optional the way it might be for someone eating meat, dairy, or eggs regularly.

Deficiency Symptoms Go Beyond Fatigue

Tiredness is the symptom everyone knows about, but it's far from the only one, and arguably not the most important. NIH lists numbness or tingling in the hands and feet as a sign of nerve problems, along with "problems with balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue"^[1]. Pale skin, heart palpitations, and unexplained weight loss round out the list^[1].

The reason this list matters: a lot of these symptoms — brain fog, mood changes, balance issues — get chalked up to stress, aging, or "just life" long before anyone thinks to check B12 status, particularly since the neurological symptoms can show up even when standard blood counts still look normal in early deficiency. If several of these sound familiar and you're in a higher-risk group (vegan, vegetarian, over 50, or on medication that affects absorption), it's worth mentioning to a doctor rather than assuming it's unrelated.

How Much You Need, and Which Form

Most adults need 2.4mcg of B12 a day; that goes up to 2.6mcg during pregnancy and 2.8mcg while breastfeeding^[1]. On the question of which supplement form is "best" — cyanocobalamin, methylcobalamin, adenosylcobalamin, hydroxycobalamin — the honest answer from NIH is that "research has not shown that any form of supplemental vitamin B12 is better than the others"^[1]. Sublingual forms and prescription injections exist for people who need higher doses or have absorption issues, but for most people a standard daily gummy is a perfectly reasonable format.

On safety, B12 "has not been shown to cause any harm, even at high doses," and there's no established upper limit^[1] — which is part of why it's a low-risk addition even if you're not certain whether you're deficient. If you want the full spectrum of B vitamins rather than B12 alone, a B-Complex covers the others (thiamin, riboflavin, niacin, B6, folate, and more) that work alongside B12 in the same energy-metabolism pathways.

Frequently Asked Questions

What's the best B12 supplement for vegans?

NIH hasn't found any supplemental form (cyanocobalamin, methylcobalamin, or others) to work better than another, so the more important factor for vegans and vegetarians is taking one consistently, not which specific form you choose.

Can B12 deficiency cause symptoms other than tiredness?

Yes — numbness or tingling in the hands and feet, balance problems, memory and mood changes, and mouth or tongue soreness are all documented symptoms, alongside pale skin and heart palpitations.

Is it safe to take B12 every day?

Yes. NIH reports that B12 has not been shown to cause harm even at high doses, and there's no established upper limit, making daily use low-risk for most people.

Will B12 give me more energy if I'm not deficient?

Not according to NIH — B12 doesn't provide energy, athletic performance, or endurance benefits in people who already get enough from their diet. See our best supplements for energy guide for the fuller breakdown.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. The content in this article is for informational purposes only and is not a substitute for professional medical advice.