Risks and limits of Vitamin D Training

The term 'Vitamin D Training' is misleading because vitamin D is a hormone, not a training agent. Evidence indicates that adequate vitamin D levels (25(OH)D > 30 ng/ml) support muscle function, bone health, and recovery, especially in deficient athletes. However, risks include toxicity from excessive supplementation (> 4000 IU/day long-term), leading to hypercalcemia and kidney stones. The evidence for performance enhancement in replete individuals is weak and mostly observational. Limits: many commercial tests are unreliable, and optimal levels are debated. Supplementation should be guided by blood tests and a healthcare provider. In summary, correcting a deficiency is beneficial, but 'training' with vitamin D lacks robust evidence. Evidence grade: human-moderate for general health benefits, mixed for athletic performance.