Meat, fish, eggs, dairy. Look at the reliable food sources of B12 and you'll notice a pattern — they're exactly the foods a plant-based diet cuts out. That's not a coincidence and it's not really about willpower or "eating clean enough." B12 is made by bacteria, not plants, and no amount of leafy greens or lentils will put it on your plate. If you've gone vegan or vegetarian and haven't thought about where your B12 comes from, this is worth ten minutes of your time.

Why plants were never going to cover this one

Vitamin B12 (cobalamin) is produced by bacteria and archaea, not by plants or animals. Animals end up with it in their tissue because they eat it, absorb it, or host the bacteria that make it in their gut. Humans don't have a reliable way to make our own, which means everyone needs a dietary source — it's just that omnivores get theirs pre-packaged in meat, fish, eggs and dairy, and vegans and vegetarians don't.

This isn't a fringe concern dreamed up by supplement brands. It's one of the few nutrients where the mainstream medical and vegan advocacy positions agree completely: fortified food or a supplement is not optional on a vegan diet, and it's frequently under-covered on a vegetarian one too. It's also one of the more thoroughly regulated nutrients on the market — under EU law, B12 carries authorised claims for normal energy-yielding metabolism, the nervous system, psychological function, red blood cell formation and reduced tiredness and fatigue, all backed by EFSA's own scientific review^[1].

How common is deficiency, actually

The numbers are higher than most people expect. A review of the published literature on cobalamin status found deficiency in roughly 92% of vegans and 77% of lacto-ovo-vegetarians who weren't supplementing, compared with around 11% of omnivores^[2]. Rates varied a fair amount study to study, and pregnant women and older adults ran higher risk across every diet group. But the direction of the finding was consistent everywhere it was measured: cut out animal products without a reliable substitute, and your B12 status drops.

That's a striking figure for a nutrient with such a simple fix. Deficiency isn't inevitable on a plant-based diet — it's what happens by default if nobody actively replaces the one thing the diet removes.

The absorption problem nobody explains properly

Here's the part that gets left out of most B12 advice: your body can't absorb it in one clean gulp, no matter how much you take. B12 relies on a stomach protein called intrinsic factor to be absorbed in the small intestine, and that system has a ceiling. At low doses, around 1–2mcg, absorption efficiency sits near 50%. Push the dose up to 500mcg and absorption efficiency drops to roughly 2%; at 1,000mcg it's closer to 1.3%^[3].

It sounds like a design flaw, but it's why supplement doses look so much bigger than the official daily requirement. The UK's recommended intake for adults is 1.5mcg a day^[4] — tiny, by supplement-label standards. Supplements are formulated at 50mcg, 100mcg, even 1,000mcg specifically to compensate for that saturation curve. You're not overdosing by taking more than 1.5mcg; you're working around a bottleneck. And because no toxic upper limit has been established for B12, there's no safety ceiling forcing the dose down^[4].

"You're not overdosing by taking more than 1.5mcg a day — you're working around a bottleneck."

What to actually check before you buy

• The dose, not just the presence of B12 — a multivitamin with 2.4mcg tucked in among thirty other ingredients isn't doing the same job as a dedicated dose built for poor absorption.
• The form — cyanocobalamin is the most stable, well-researched and widely recommended form for vegans; your body converts it into the active forms it needs^[4].
• What else is riding alongside it — folate and iron both feed into the same red blood cell production pathway B12 supports, and both are separately harder to get enough of on a plant-based diet.

That third point is the one most B12-only products miss. If you've moved away from meat, you've likely also reduced your most efficient dietary iron source at the same time — which is exactly why Oxford Origins built its Vegan Iron Complex around all three together rather than isolating B12 on its own.

The Golden Pick

Vegan Iron Complex with Vitamins C, B12 & Folic Acid

100mcg B12 · 400mcg folic acid · 14mg iron

£9.95● OUT OF STOCK

View Vegan Iron Complex →

One capsule a day covers 100mcg of B12 as cyanocobalamin alongside 400mcg of folic acid and 14mg of iron as ferrous fumarate — non-GMO, and free from dairy, soy, gluten and artificial colours or flavours, so it sits comfortably within a vegan or vegetarian diet rather than working against it.

Signs it's already running low, and when to see your GP

Early B12 deficiency is easy to miss because the symptoms are so generic: low energy, poor concentration, a sore or unusually smooth tongue, pins and needles, low mood. Left long enough, it can progress to nerve damage that doesn't always fully reverse, which is the main reason it's worth catching early rather than waiting to see if the tiredness passes^[5].

Not every case is dietary, either. Pernicious anaemia — an autoimmune condition that stops the body producing intrinsic factor — is the most common cause of B12 deficiency in the UK regardless of diet, and it needs a different treatment route (usually injections rather than oral supplements) because the absorption pathway itself is broken^[5]. If you're supplementing consistently and still getting symptoms, that's a GP conversation and a blood test, not a reason to just take more tablets.

None of this is complicated once you know it. It's one nutrient, one clear gap, and a fix that takes about as long as swallowing a capsule with breakfast. Getting it right isn't about perfection — it's just about not leaving the one thing your diet can't cover to chance.

Frequently asked questions

What are the early signs of B12 deficiency?

Fatigue, low mood, poor concentration, a sore or smooth-looking tongue, and tingling in the hands or feet are the most commonly reported early signs. They're easy to write off as general tiredness, which is part of why deficiency often goes unnoticed until it's more advanced.

Can I get enough B12 from fortified food alone?

Potentially, if you're eating fortified plant milk, nutritional yeast or fortified cereal consistently and in reasonable amounts across the day — B12 absorbs better in smaller, frequent doses than one large one. In practice, most people find a daily supplement more reliable than tracking fortification across several products.

Is 100mcg of B12 too much to take every day?

No. Because absorption efficiency drops sharply as the dose rises, supplement doses are deliberately set well above the 1.5mcg daily requirement to compensate. No upper safety limit has been set for B12, as no toxic effects have been identified even at high intakes.

What's the difference between a B12 supplement and a B12 injection?

Oral supplements rely on your gut absorbing B12 through intrinsic factor, which works fine for most dietary deficiency. Injections bypass digestion entirely, which is why they're used for pernicious anaemia or other absorption disorders. If you've recently started injections and felt worse before feeling better, we've covered why that happens and what's normal in more detail.

Sources

1. European Commission / EFSA — Commission Regulation (EU) No 432/2012 establishing authorised health claims for vitamin B12, cited for energy metabolism, nervous system, psychological function, red blood cell formation and fatigue claims. https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:136:0001:0040:en:PDF
2. Pawlak R. — The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature, cited for deficiency prevalence rates in vegans and vegetarians. https://pubmed.ncbi.nlm.nih.gov/24667752/
3. StatPearls / NCBI Bookshelf — Cyanocobalamin, cited for B12 absorption rates at varying doses. https://www.ncbi.nlm.nih.gov/books/NBK555964/
4. The Vegan Society — Vitamin B12, cited for UK recommended daily intake, recommended supplement form, and absence of an upper safety limit. https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-b12
5. NHS inform — Vitamin B12 or folate deficiency anaemia, cited for symptoms and causes including pernicious anaemia. https://www.nhsinform.scot/illnesses-and-conditions/nutritional/vitamin-b12-or-folate-deficiency-anaemia/

At Oxford Origins, your wellbeing is our priority, and although we pride ourselves on our expertise in nutrition and supplementation, it's important to acknowledge the individuality of each person. Articles published by Oxford Origins are not intended to treat, diagnose, cure or prevent any disease, or replace the advice of your GP. We always recommend consulting with a healthcare provider if you encounter any health concerns, and we'll always be here to support you so you're never alone on your journey.