What role does B12 play in Sport?

The provided knowledge sources contain no information about the role of vitamin B12 in sports. Therefore, the following answer is based on general physiological knowledge, not on the given contexts. B12 is essential for energy production (methylation in the citric acid cycle), red blood cell formation, and nervous system function. A deficiency can lead to fatigue, reduced performance, and increased injury risk. Athletes, especially vegans or older individuals, may have subclinical deficiency. However, there is no strong evidence that B12 supplementation improves athletic performance in those with adequate levels. Direct-to-consumer tests (like MyBody-X) often measure total B12, not the active form (holotranscobalamin), complicating interpretation. Genetic variants (e.g., in MTHFR) can affect B12 metabolism, but the provided contexts lack such data. Overall, evidence for an ergogenic effect of B12 in sports is weak and mostly mechanistic, not from controlled trials. Safety note: excessive B12 intake is considered safe, but self-supplementation without deficiency diagnosis is not recommended.