Vitamin B-12 plays a vital role in the formation of red blood cells, which carry oxygen from the lungs to the rest of the body -- a necessity for athletic performance. Vitamin B-12 deficiency can take up to 30 years to show symptoms but ultimately results in weakness, lethargy and anemia.
B-12 Requirements and Sources
The recommended daily allowance of B-12 for adults is 2.4 mcg per day. During pregnancy and lactation, the recommended daily allowance is increased to 2.6 to 2.8 mcg per day. The only food sources of vitamin B-12 are animal products, such as meat, poultry, fish, milk and eggs. Vegetarians can get the B-12 they need from the milk and eggs that they eat, but vegans need to rely on fortified foods like soy milk and tofu or take a vitamin B-12 supplement.
Causes of Deficiency
Except in cases of special dietary restriction, inadequate consumption of B-12 is not usually the cause of deficiency. More often, inadequate absorption of B-12 is at fault. Some people, especially the elderly, have low levels of intrinsic factor, a protein necessary for absorption of B-12 in the small intestine. Calcium must also be present for the absorption of B-12, which is sometimes lacking in the elderly. In cases of exceptionally low absorption, pharmacological doses of vitamin B-12 may be necessary. Vitamin C can block the absorption of B-12, so taking supplements of both vitamins at the same time may decrease the utility of the B-12 supplement.
Supplementation in Athletes
An athlete who is deficient in vitamin B-12 will not perform at their peak potential. Although many athletes eat a diet that contains adequate amounts of B-12, athletes eating a calorie-restricted diet or abstaining from animal products may be at risk of B-12 deficiency. Supplementation to correct deficiency will have a positive impact on athletic performance, but there is no evidence that taking supplements beyond the recommended daily allowance will improve performance beyond the correction of deficiency.
Toxicity
While there does not seem to be any benefit to taking large doses of supplemental vitamin B-12, there is also no evidence that large doses are harmful. Absorption of B-12 decreases as intake increases. At very low levels of intake, approximately 80 percent of the vitamin B-12 ingested is absorbed. As intake increases, the absorption drops -- ending up at about 3 percent of intake. Excess B-12 that is not absorbed passes out of your body as waste rather than building up and posing a toxicity threat.
References
- "Advanced Nutrition and Human Metabolism: Third Edition"; James L. Groff and Sareen S. Gropper; 2000
- "Medicine and Science in Sports and Exercise"; Nutrition and Athletic Performance; Nancy Rodriguez, et al.; 2009
- "Nutritional Assessment of Athletes"; Judy A. Driskell and Ira Wolinsky; 2010
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