Vitamin B12

Vitamin B12 (cobalamin) is a water-soluble vitamin needed for the formation of red blood cells, DNA synthesis and the healthy functioning of the nervous system. It is the nutrient most often discussed in connection with veganism, because plant foods do not contain reliable amounts of the active vitamin. Nutrition organisations including The Vegan Society, the Academy of Nutrition and Dietetics and the NHS agree that vegans should obtain B12 from fortified foods or supplements.

Where vitamin B12 comes from

Vitamin B12 is made only by certain bacteria and archaea. It is not produced by plants or animals themselves. Farmed animals obtain it from bacterial activity in their digestive systems or, increasingly, from cobalt or B12 supplements added to their feed. Animal products therefore contain B12 as a result of microbial production rather than as an inherent property of animal flesh, milk or eggs.

Some plant foods have been promoted as B12 sources, but these claims are not supported by major health bodies:

• Spirulina and many seaweeds contain mainly B12 analogues (pseudovitamin B12) that are inactive in humans and may interfere with tests.
• Fermented foods such as tempeh and miso contain variable and generally unreliable amounts.
• Unwashed produce and soil bacteria are not considered a safe or dependable source.

Why vegans need to supplement

The body can store several years’ worth of B12 in the liver, so deficiency may take a long time to appear after a diet change. This delay can give a false sense of security. Deficiency can cause megaloblastic anaemia, fatigue, numbness or tingling, problems with memory and mood, and in severe or prolonged cases, irreversible nerve damage. Low B12 status also raises blood levels of homocysteine, which has been associated with cardiovascular disease.

Because there is no reliable unfortified plant source, the scientific consensus is that every vegan, regardless of age, should have a dependable source of B12. This is particularly important during pregnancy, breastfeeding and childhood (see vegan pregnancy and children).

Recommended intakes

Reference values differ between authorities:

Supplement regimens

The amount of B12 absorbed from a single dose falls as the dose increases, because the intrinsic-factor absorption pathway becomes saturated after roughly 1–2 µg. Only a small percentage of a large dose is absorbed by passive diffusion. For this reason, recommended amounts depend on how often B12 is taken. The Vegan Society advises one of the following three options:

1. Eat fortified foods two or three times a day to get at least 3 µg of B12 a day; or
2. Take one B12 supplement daily providing at least 10 µg; or
3. Take a weekly B12 supplement providing at least 2,000 µg.

The Vegan Society notes that these options are designed to provide enough B12 even taking reduced absorption at higher doses into account. It also states that taking more than 5,000 µg a week is not advised. Other dietetic organisations give broadly similar guidance, and many multivitamins designed for vegans include B12.

Cyanocobalamin is the most widely studied and most stable supplement form. Methylcobalamin and other forms are also sold, though some organisations note that evidence for them is more limited.

Fortified foods

Common fortified products include:

• many plant-based milks and yoghurts;
• some breakfast cereals;
• fortified nutritional yeast (not all brands are fortified);
• yeast extract spreads in some countries;
• some meat alternatives.

Fortification levels vary by brand and country, so labels should be checked. Relying on fortified foods requires eating them consistently across the day.

Testing

Serum B12 is the most common blood test, but it can appear normal even when tissue levels are low, and B12 analogues may distort results. Markers such as methylmalonic acid (MMA), holotranscobalamin and homocysteine can give a more accurate picture. People with symptoms, those who have not supplemented reliably, and anyone planning a pregnancy may wish to ask their doctor about testing.

Safety

B12 has low toxicity, and no tolerable upper intake level has been set by the US Institute of Medicine or EFSA. Some medications, including metformin and proton pump inhibitors, can reduce B12 absorption, and absorption tends to decline with age.

This article is for general information. Individuals should consult a doctor or registered dietitian for personal advice, especially if they have symptoms or medical conditions.

See also

• How to Go Vegan
• Meal planning
• Vegan diet and health