Vitamin B₁₂

Vitamin B₁₂ is the most chemically complex of all the vitamins. It contains the mineral cobalt (thus the name “obalamin”) and, while essential for all cell function, has a major involvement in red blood cell formation, folic acid metabolism, DNA synthesis, and nerve development.

Dietary sources of this vitamin are mainly foods of animal origin (meats, eggs, dairy products); it is essentially absent from plant foods. A small amount of absorbable vitamin B₁₂ may also be produced by gut bacteria.²³ Vegetarian athletes who avoid all foods of animal origin (i.e., they do not eat meat, nor do they consume eggs or dairy products) would therefore be at risk for vitamin B₁₂ deficiency.

B₁₂ deficiency results in pernicious anemia, a form of anemia that most commonly occurs in the elderly with compromised stomach function. The stomach normally produces intrinsic factor, which is required for vitamin B₁₂ absorption. Without intrinsic factor, even a normal dietary intake of vitamin B₁₂ will result in deficiency disease because of malabsorption. Symptoms of deficiency include fatigue, poor muscular coordination (possibly leading to paralysis), and dementia.

Athletes have abused vitamin B₁₂ for years. It was (and continues to be) common for many athletes to be injected with large amounts of vitamin B₁₂ (often 1-gram injections) before competitions.^24,25 Despite the commonality of this strategy, there is no evidence that vitamin B₁₂ does anything whatsoever to improve performance when taken in excess.^26-28

It certainly makes sense that athletes consume foods that will help them avoid deficiencies of any kind, including B₁₂ deficiency. The resulting anemia would clearly affect performance by reducing oxygen-carrying capacity, leading to reduced endurance. Potentially, muscular coordination could also be impaired. Unless someone has a genetic predisposition for B₁₂ malabsorption (typically because of an inadequate production of intrinsic factor), there is no basis for taking supplements if a balanced mixed-food diet is consumed. Vegan athletes, on the other hand, have good reason to be concerned about vitamin B₁₂ status. A supplement providing, on average, the DRI of 1.8 to 2.4 micrograms per day for vegan athletes makes good sense, as does the consumption of foods that are fortified with vitamin B₁₂ (such as some soy milk products).