Comparison of Vitamin D Sufficiency Between Indoor and Outdoor Elite Male Collegiate Athletes

This study compared vitamin D sufficiency between indoor and outdoor elite athletes. We also evaluated the association between vitamin D level, body composition, and stress fractures incidence. 27 outdoor elite male collegiate athletes (field hockey players) and 21 indoor elite male collegiate athletes (fencing players) were enrolled. Participants' demographic information including past fractures were recorded. Furthermore, all the athletes' body compositions including percentage of body fat were measured. Blood samples were collected to test serum calcium, phosphorus, and 25(OH)D. levels. Participants were classified into three groups: vitamin D sufficiency (serum 25(OH)D levels of ≥30 ng/ml), vitamin D insufficiency (serum 25(OH)D levels of <30 ng/ml), and vitamin D deficiency (serum 25(OH)D levels of <20 ng/ml). The indoor athletes showed significantly higher mean percentage of body fat than outdoor athletes, 12.2 ± 3.2% and 9.7 ± 3.7%, respectively. The serum 25(OH)D levels of indoor athletes were significantly lower than those of outdoor athletes, 15.3 ± 3.3 ng/mL and 24.9 ± 4.5 ng/ml, respectively (P < 0.001). Furthermore, the indoor athletes showed a significantly higher rate of vitamin D deficiency than the outdoor athletes, 19 of 21 (90.5%) and 5 of 27 (18.5%), respectively (P < 0.001). The cohort of outdoor athletes with stress fractures' history had significantly lower serum 25(OH)D levels than those without history of any fractures, 21.1 ± 4.3 ng/ml and 26.4 ± 3.0 ng/ml, respectively (P < 0.05). In conclusion, a majority of the indoor elite athletes were vitamin D-deficient. The serum 25(OH)D levels were significantly higher in outdoor elite athletes. However, lower serum 25(OH)D levels might be associated with stress fractures among outdoor athletes.