Vitamin
Foods high in vitamin B12 and what vegans need to watch
Vitamin B12 is essentially absent from plant foods. On a fully plant-based diet it is close to the one nutrient that genuinely requires supplementation.
Highest sources
Ranked among the ingredients covered here. Reference amounts vary slightly between entries, so read this as a rough comparison rather than an exact order.
What it does
It is needed to form red blood cells and to maintain the myelin sheath around nerves. Prolonged deficiency produces anaemia and neurological symptoms such as tingling in the hands and feet and impaired balance, and the nerve damage may not fully reverse.
Recommended intake
The usual adult reference is 2.4 µg a day, slightly higher in pregnancy and lactation. Because the liver stores several years' worth, deficiency symptoms appear slowly.
What affects absorption
It must bind intrinsic factor, secreted by the stomach, to be absorbed. Absorption drops after gastric surgery, in older adults with reduced stomach acid, and with long-term use of metformin or acid-suppressing drugs. In those cases shortage can develop regardless of how much you eat.
What to watch out for
Being water-soluble, no toxicity from excess has been reported. But high folate intake can mask the anaemia of B12 deficiency and let nerve damage go unnoticed. On a plant-based diet, a blood test is the safe way to check.
Sources
The databases and health authorities this article's nutrition figures and health statements draw on.