Vitamin B12, or cobalamin, is an important nutrient. It is an essential nutrient, meaning in this case not that it is necessary for good health—though it is—but it is not produced in the body, and must be consumed in food or supplements. Vitamin B12 is needed to produce red blood cells and effects the functioning of the brain and nervous system. It is also used to treat cyanide poisoning, to essentially suck the cyanide out of the bloodstream so it can be passed harmlessly.
It is also, unsurprisingly, used to treat B12 deficiency. B12 deficiency is rare, because most people consume more than they need and the body stores the excess—as much as five years’ worth—primarily in the liver. Certain medical conditions or treatments can diminish the body’s ability to absorb or use B12, however, and this can lead to symptoms such as fatigue, depression, and impaired memory. More severe deficiency can result in irreversible damage to the brain and nervous system, leading to dementia.
Dietary sources of vitamin B12 include in fish and shellfish, meat, eggs, and dairy products. Vitamin B12 is often added to livestock feed in the United States, so farmed meat generally has particularly high levels. Vegans, who don’t eat eggs or dairy, often need to take supplements, which are typically made from a synthetic form called cyanocobalamin. This molecule does not occur in natural sources but is easily converted by the body into the natural forms of the vitamin. Vegetarians who do eat eggs and dairy products may still need supplements, because vegetarian diets often feature a lot of soy, which can impair B12 absorption.
Scientists have recently found signs of a previously unknown role for vitamin B12. In conjunction with the compound taurine—known from energy drinks, but actually an important nutrient in its own right, with important roles in the functioning of the cardiovascular and central nervous systems—B12 helps regulate the creation of new bone tissue.
This means doctors may be able to add osteoporosis to cyanide poisoning and vitamin B12 deficiency on the list of conditions treated with B12. While it can stop or even reverse cognitive decline resulting from B12 deficiency, there is no indication B12 can improve cognitive function in healthy people.