Cycling training influences gut microbiota and vitamin B12 requirements

Physical training in cycling can alter the composition and activity of the gut microbiota. Factors such as weekly volume, session intensity, heat, and diet affect microbial diversity, with active cyclists often showing a richer microbiome and higher levels of short‑chain fatty‑acid‑producing bacteria that support intestinal barrier function, energy metabolism and inflammation regulation. However, separating the effects of exercise from lifestyle variables—higher carbohydrate intake, fermented foods, supplements and rest patterns—remains challenging.

Vitamin B12 (cobalamin) is essential for red‑blood‑cell formation, DNA synthesis and nervous‑system health, all of which influence oxygen transport and endurance. In cyclists with a confirmed deficiency, supplementation can correct anemia‑related fatigue and improve performance. When levels are normal, additional B12 offers no ergogenic benefit, and fatigue is more likely linked to iron status, energy availability, infection or overtraining.