Nutrition
By Priya Nair · Updated August 18, 2026 · Fact-checked
Vitamin B12 is one of those nutrients most people never think about until a blood test raises an eyebrow. It is not glamorous. It does not have a supplement aisle built around it the way protein or collagen does. But it sits behind red blood cell production and nerve function, and running low on it produces symptoms so vague that people often put up with them for months before anyone checks.
What B12 actually does
Three jobs matter most. B12 helps the body make healthy red blood cells, which is why deficiency shows up as a particular type of anaemia. It is needed to build and maintain the protective sheath around nerves. And it works alongside folate in the reactions that make DNA.
Unlike most water-soluble vitamins, B12 is stored — mainly in the liver — and the stores can be substantial. That is why deficiency tends to develop slowly, sometimes over years, and why someone can change their diet and feel fine for a long time before anything shows up.
Signs you might be running low
This is the frustrating part. Early symptoms are nonspecific enough to be blamed on almost anything:
- Persistent tiredness and a sense of being out of breath on stairs you used to manage
- Pale skin, or a smooth, sore tongue
- Pins and needles, numbness, or an odd unsteadiness in the feet
- Trouble concentrating, forgetfulness, low mood
- Dizziness or a racing heartbeat
The neurological symptoms are the ones worth taking seriously, because unlike the blood changes, they do not always fully reverse once treatment starts. Tingling in the hands and feet that has been building for months deserves a doctor rather than a supplement bought on a hunch.
Who is most at risk
Some people are far more likely to run low than others:
- Vegans and long-term vegetarians. B12 occurs naturally almost only in animal foods, so a plant-based diet without fortified foods or a supplement will eventually run the stores down.
- Adults over about 50. Stomach acid production declines with age, and acid is needed to release B12 from food.
- People on long-term acid-reducing medication such as proton pump inhibitors, for the same reason.
- Anyone taking metformin for a long stretch, which can interfere with absorption.
- People who have had stomach or bowel surgery, including weight loss surgery, or who have coeliac or Crohn’s disease.
- People with pernicious anaemia, an autoimmune condition that blocks the absorption pathway entirely.
Where to find it in food
Animal foods do the heavy lifting. Shellfish and liver are the standouts by a wide margin — a single serving of clams or beef liver supplies many times a day’s worth. After that, the practical everyday sources are:
- Salmon, trout, tuna and sardines
- Beef, lamb and pork
- Eggs, particularly the yolks
- Milk, yoghurt and cheese
- Fortified breakfast cereals
- Fortified plant milks and nutritional yeast, which matter enormously on a plant-based diet
Adults generally need somewhere around 2.4 micrograms a day, with slightly more in pregnancy and breastfeeding. Most people eating animal products comfortably clear that without trying. If you already track nutrients like omega-3s or iron, B12 is worth a glance at the same time.
Absorption is the part people miss
Getting enough B12 into your mouth is only half the story. Food-bound B12 has to be freed by stomach acid, then bound to a protein called intrinsic factor, then absorbed further down in the small intestine. Break any link in that chain and intake stops mattering very much.
This is why an older adult eating plenty of meat can still end up deficient, and why supplements sometimes work when a diet overhaul does not. Fortified foods and supplements contain B12 in a free form that does not need stomach acid to release it, which is exactly why they are recommended for people over 50.
Supplements: forms and what to know
Cyanocobalamin is the cheapest and most studied form, and it is stable and effective for most people. Methylcobalamin is marketed as more natural and better absorbed; the evidence for a meaningful advantage in healthy people is thin. Sublingual tablets are not clearly superior to swallowed ones, despite the marketing.
B12 has no established upper limit, because excess is largely excreted rather than stored to harmful levels. That is not permission to megadose without reason — but it does mean the risk profile is favourable, which is one reason doctors are relaxed about recommending it to people in the at-risk groups. Injections are reserved for absorption problems such as pernicious anaemia, where oral supplements cannot do the job reliably.
Getting tested
A standard serum B12 test is the usual starting point, though it has limitations — results in the low-normal range can be hard to interpret. If symptoms suggest deficiency but the number looks borderline, doctors sometimes add a methylmalonic acid or homocysteine test, both of which rise when B12 is genuinely lacking at the cellular level.
Worth knowing: high folate intake can mask the blood changes of B12 deficiency while the nerve damage quietly continues. That is one reason self-treating a suspected deficiency with a general B-complex is a poor substitute for a test. The same principle applies to suspected iron deficiency — confirm before you supplement.
Questions people ask
How long does it take to correct a B12 deficiency?
Blood counts usually start improving within a couple of weeks of treatment and energy often follows. Neurological symptoms take considerably longer and may not resolve completely if they have been present for a long time, which is the main argument for not waiting.
Can you get enough B12 on a vegan diet without supplements?
Realistically, no. Reliable plant sources do not exist outside fortified products. Most dietitians recommend that vegans use fortified foods, a supplement, or both rather than relying on things like seaweed or fermented foods, which are not dependable sources.
Does B12 give you energy?
Only if you were short of it. Correcting a deficiency can make a dramatic difference to fatigue. Taking extra when your levels are already fine does not appear to add anything, despite what the energy shot on the counter implies.
The takeaway
B12 deficiency is common, easy to miss, and straightforward to fix once someone actually looks for it. If you are vegan, over 50, on long-term acid-reducing medication or metformin, or you have unexplained fatigue with tingling in your hands or feet, ask for a test rather than guessing. Everyone else can cover it comfortably through ordinary food and get on with their day.
This article is for general information only and is not medical advice. Speak with a qualified healthcare professional before starting any supplement or if you have symptoms that concern you.