Vitamin D Supplements in Sports: A Long Run for a Short Jump.

Recent Recommendations in Sports Two recent articles are examples. A study of elite ballet dancers recommends testing ferritin and vitamin D levels annually, noting that “a deficit in vitamin Dmay cause deterioration of iron status and increase the risk of anemia” (1). Most of the female dancers (68%), especially those on restricted diets, had low ferritin; this is no surprise. In contrast, vitamin D status was generally adequate. In any case, the notion that low vitamin D can cause iron deficiency anemia is wrong. The authors cite a meta-analysis of seven observational studies of low vitamin D and “anemia.” Two were U.S. studies; neither tied low vitamin D to iron deficiency anemia (2,3). Low vitamin D can “travel with” low ferritin, but one does not cause the other. The other recent article recommends VDS for endurance cyclists training intensely (4). It notes conflicting results in a narrative review, and cites one study, showing that VDS boost aerobic fitness in soccer players (5). But in that study, V̇O2 max rose 2.6% in those on VDS (P = 0.03) versus 2.2% in those not on VDS (P = 0.053). All told, weak support for recommending VDS to endurance cyclists. I will return to VDS for athletes. First, the track record for VDS in the practice of medicine.