Due to the absence of animal and dairy products, vegans are at a higher risk of developing a vitamin B12 deficiency (cobalamin). Cobalamin is part of so-called water-soluble vitamins, those that cannot be accumulated in the bodyIt is synthesized by anaerobic microorganisms in the rumen of cattle and sheep, and humans typically consume preformed cobalamin from animal products, which are the major dietary source of B12. Plant sources of cobalamin are unusualunless the plant has been contaminated by manure or animal waste.
Vegan and Vitamin B12
Cobalamin is essential for normal functioning of the nervous system, homocysteine metabolism and DNA synthesis. Insufficient cobalamin can lead to morphological changes of blood cells and allo development of hematological and neurological symptoms, such as megaloblastic anemia and neuropathy. Long-term cobalamin deficiency can lead to irreversible neurological damage and data indicate that veganism can lead to a deficiency if cobalamin is not supplemented. I data from the EPIC-Oxford cohort study in the UK indicated that approximately 50% of vegan participants were deficient in vitamin B12. A further 21% of vegans were classified as having very low levels. Interestingly, despite 20% of participants consuming a B12 supplement, blood vitamin levels between those who did and those who did not take it were not different, suggesting that the cohort’s supplementation practices were inadequate to achieve the sufficiency of B12.
Sources of vitamin B12 for vegan sportsmen
The sources of vitamin B12 suitable for a vegan diet they include breakfast cereals fortified with B12 and nutritional yeast, as well as nutritional supplements. The vitamin B12 supplements usually contain cianocobalaminaalthough other forms such as the are available metilcobalamina and thehydroxycobalaminthe latter only on medical prescription. The body appears to have a limited ability to absorb oral vitamin B12 supplementslimited by the presence of intrinsic factor, a glycoprotein secreted by the parietal cells of the stomach that combines with B12 before uptake in the distal ileum via receptor-mediated endocytosis.
For a 500 μg oral supplement, only about 10 μg could be absorbed. Because of this poor bioavailability, sublingual drops, lozenges, and transdermal products have been developed and marketed with claims that they offer better absorption, but as of this writing, no research could be found to support these claims.
Vitamin B12 supplementation for vegan sportsmen
The obligation to supplementing with vitamin B12 is important for vegans, who are advised to consume fortified foods and/or take a daily supplement to ensure adequate intake of this vitamin. The Dietary Reference Intake (DRI) for vitamin B12 is 2.4 μg/day for adults of both sexes, and some authors have advised vegans to consume up to 6 μg x day of supplemental B12. In cases where adequate B12 status cannot be achieved through oral supplementation and fortified food products alone, vegans may need to have serum levels monitored by a physician if a deficiency is suspected; in some contexts subcutaneous or intramuscular injections may also be indicated; close monitoring of B12 status may be necessary for some vegan athletes.
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