Vitamin B12 (Cobalamin): Requirements, Indian Sources and Deficiency

Vitamin B12, also called cobalamin, is the one vitamin that no plant makes. Microorganisms produce it, animals store it, and people get it from milk, curd, eggs, fish and meat, or from fortified foods and supplements. ICMR-NIN's Nutrient Requirements for Indians (2020) sets the allowance at 2.2 mcg a day for adult men and women. That is a very small amount, yet surveys keep finding Indians short of it, because a largely vegetarian plate with little dairy supplies well under that figure. This entry belongs to the vitamins section of the handbook.

What is vitamin B12 and what does it do?

Vitamin B12 is a large, cobalt-containing molecule that human cells need for only two enzymes, and both matter a great deal. The first, methionine synthase, works together with folate to supply the building blocks of DNA, so a shortage slows the production of red blood cells and leaves them fewer and larger than normal. The FAO and WHO expert report describes how a lack of B12 also strips the insulating layer from peripheral nerves and the spinal cord, which is why deficiency can show as numbness and tingling as well as anaemia.

Absorption takes several steps. Stomach acid frees B12 from the protein in food, a carrier called intrinsic factor binds it, and the complex is taken up at the far end of the small intestine. The liver holds a reserve, which is why a poor intake can go unnoticed for years.

How much vitamin B12 do you need in India?

ICMR-NIN's 2020 report sets 2.2 mcg a day for everyone from the age of four upwards, 1.2 mcg for infants and children up to three, an extra 0.25 mcg in pregnancy and an extra 1.0 mcg during breastfeeding. The estimated average requirement for adults is 2.0 mcg. The committee started from a daily loss of 1 mcg and doubled it, because stable isotope studies at St John's Research Institute in Bengaluru found that about half of the B12 in food is absorbed.

The two sets of figures are close for adults. ICMR-NIN's earlier 2010 value was 1 mcg, so the 2020 allowance more than doubled the Indian recommendation. The 2020 report lists tolerable upper limits for several nutrients, and vitamin B12 is not among them.

Why do vegetarian Indians run low on B12?

Because the only natural vegetarian sources are milk and its products, plus eggs for those who eat them, and many adults take too little of either to reach 2.2 mcg. ICMR-NIN's Dietary Guidelines for Indians (2024) names B12 as a nutrient of concern for vegetarians and adds, plainly, that milk has only a small amount. A cup of chai may hold a quarter of a glass of milk. Unless curd, paneer or a glass of milk appears every day, the total stays low.

Diet is not the whole story. In one study the BOND review cites, 67 per cent of 442 adult men in Pune had serum B12 below 150 pmol/L, and vegetarians carried four times the risk of omnivores. Absorption also falls with age, with long use of acid-suppressing medicines and after stomach surgery. The related entry on iron in the handbook explains why the two shortages often travel together.

Indian food sources of vitamin B12

The Indian Food Composition Tables 2017 did not analyse vitamin B12, so there is no national table of B12 in Indian foods to quote, and NNWA's nutrient rankings of Indian foods carry no B12 list for that reason. The figures below come from two places: milk sampled from Pune's dairies in an Indian trial, and the United States values summarised in the Biomarkers of Nutrition for Development review. Treat them as a guide to scale.

Two things stand out. Fish and liver carry far more B12 than chicken, so a fish curry does more for B12 than a chicken one; the fish and seafood tables list the Indian species. And the Pune milk figures are lower than the American ones, so a glass of milk here may not deliver a full microgram. For vegetarians the milk and dairy tables are the place to plan from.

Do fortified foods under FSSAI rules close the gap?

Only partly, and less than the logo suggests. FSSAI's Fortification of Foods Regulations, 2018 allow B12 to be added to atta, maida and rice at 0.75 to 1.25 mcg per kilogram, and to breakfast cereals, pasta, noodles and bakery items at 0.08 to 0.16 mcg per 100 g. Fortified milk under the same regulations carries added vitamins A and D, not B12. Every fortified pack must name the added nutrient and carry the logo set out in the regulations.

The arithmetic is plain: a household that switches both its atta and its rice to fortified versions gains roughly 0.3 to 0.5 mcg a day per adult, between 14 and 23 per cent of the allowance. Supplements are regulated separately. FSSAI's health supplement regulations cover vitamin tablets and capsules at up to one recommended dietary allowance, and the 2021 compendium's schedule lists cyanocobalamin and hydroxocobalamin as the permitted forms of B12. The label must carry the words HEALTH SUPPLEMENT, the amount per serving as a percentage of the ICMR allowance, and the advisory NOT FOR MEDICINAL USE.

Too little: deficiency signs and the groups at risk

A shortage shows in the blood and in the nerves. The classic blood picture is megaloblastic anaemia, with tiredness and pallor. The nerve picture is neuropathy, felt as tingling or numbness in the hands and feet, and it can appear without any anaemia. The BOND review warns that nerve symptoms left untreated for more than six months to a year may not fully recover. Among infants of mothers with very low B12, it reports developmental delays of which only about half are reversed by later supplementation.

The Indian numbers are large. The Comprehensive National Nutrition Survey 2019, as tabulated in the Dietary Guidelines for Indians, found B12 deficiency in 13.8 per cent of children aged one to four, 17.2 per cent of those aged five to nine and 30.9 per cent of adolescents aged ten to nineteen. In the Pune trial of young vegetarian postgraduates, 57 per cent were deficient at the start. Adult figures come from city studies and should be read as local.

How is vitamin B12 status tested?

The first test is serum vitamin B12, usually ordered with a complete blood count. The Pune studies used about 150 pmol/L as the line for deficiency, and the American metformin trial used 203 pg/mL, but each laboratory prints its own reference range and the report should be read against that. A borderline value does not settle the matter either way.

When the picture is unclear a doctor may add holotranscobalamin, methylmalonic acid or homocysteine. The FAO and WHO report describes methylmalonic acid as the more specific sign, with the caution that it also rises when the kidneys are not working well, while homocysteine rises with low folate too. Which test to add, and what a result means for you, is a clinical judgement. The longer guide on vitamin B12 for vegetarians walks through a typical report.

What does the evidence say about milk, tablets and metformin?

Three findings are worth knowing, and their strength differs. First, ordinary milk helps. In the Pune intervention trial, B12-deficient vegetarians who drank 400 ml of unfortified milk a day for 14 days improved their B12 markers. It was a short study of 51 volunteers, so it shows direction only.

Second, tablets can work as well as injections for many people. A Cochrane review of 2018 found three randomised trials with 153 participants comparing oral and injected B12 for deficiency, and no clinically relevant difference in blood levels where high-dose tablets were used. The authors graded the evidence as low quality, and the trials lasted only three to four months. The choice of route and dose remains the treating doctor's.

Third, metformin lowers B12 over time. In the long follow-up of a large American diabetes prevention trial, low B12 was found in 4.3 per cent of people on metformin at five years against 2.3 per cent on placebo, and the odds of deficiency rose by 13 per cent with each year of use. A randomised trial of this size is strong evidence, and it supports periodic testing. It is not a reason to stop the medicine.

A worked example: one vegetarian day in Pune

This is an illustration, not a real person. Take a 28-year-old lacto-vegetarian software engineer in Pune who eats no eggs, has two cups of chai, and takes half a katori of curd with lunch. Her allowance is 2.2 mcg. The steps below use the Pune milk range and the BOND yoghurt value, which works out to about 0.5 mcg per 100 g.

Common mistakes and myths about B12

The commonest mistake is to treat tiredness with iron alone. Iron deficiency and B12 deficiency both cause anaemia, and iron tablets do nothing for the second. The opposite mistake also happens: the FAO and WHO report cautions that large amounts of folic acid, above 1,000 mcg a day, can correct the anaemia of B12 deficiency while the nerve damage continues unseen. A normal haemoglobin is therefore not proof that B12 is adequate.

Is too much B12 a risk, and when should you see a doctor?

ICMR-NIN's 2020 report sets no upper limit for B12, and the body limits its own uptake: the FAO and WHO report explains that the intrinsic factor route is limited to about 1.5 to 2.0 mcg a meal, and that only 1 to 3 per cent of any larger oral amount is absorbed by simple diffusion. That is not a licence to self-prescribe large doses, which can make a blood test look normal and hide the question of why absorption failed.

See a doctor, and do not rely on diet or an over-the-counter tablet, if you have tingling, numbness or anaemia that has not responded to iron. Pregnant and breastfeeding women on a vegetarian or vegan diet, parents of an infant who is slow to develop, and anyone with stomach or bowel disease should also be assessed medically. Do not stop metformin or an acid-suppressing medicine because of what you have read here; ask the prescriber about testing.

NNWA courses that teach this

Vitamin requirements and deficiencies are part of what NNWA, a private skill academy in Kolkata, teaches online in English and Hindi. Its courses, including the Diploma in Nutrition and Public Health Nutrition, train people to plan food for healthy clients and to refer medical cases such as a suspected deficiency to a doctor. None of them is a degree or a dietitian qualification.