The effect of body composition and BMI on 25(OH)D response in vitamin D-supplemented athletes

Fat mass is inversely associated with vitamin D status, and athletes with the most adipose tissue may have the greatest risk for insufficient (25(OH)D 20–32 ng mL⁻¹) or deficient (25(OH)D < 20 ng ml⁻¹) status. The effects of fat and lean mass on 25(OH)D change in response to vitamin D supplementation have yet to be elucidated in athletes. In addition, vitamin D has a known role in bone health yet a link between short-term changes in 25(OH)D and bone turnover in indoor athletes have not yet been described. Thirty-two collegiate swimmers and divers (19 male, 13 female; 19 (1) years) participated in a 6-month randomized controlled trial and consumed either 4000 IU d⁻¹ of vitamin D₃ (n = 19) or placebo (PLA; n = 13). Anthropometry and blood collection of 25(OH)D, bone-specific alkaline phosphatase (B-ALP) and N-terminal telopeptide (NTx) occurred at three time points. Dual-energy X-ray absorptiometry measured body composition analysis at baseline and endpoint. In the vitamin D group, BMI was negatively correlated with 6-month 25(OH)D change (R = −0.496; P =.03) and a stronger predictor of 25(OH)D change (P =.04) than ultraviolet B exposure and fat mass change. Athletes in the high bone turnover group showed significantly greater losses of 25(OH)D over 6-months compared to athletes in the low bone turnover group (P =.03). These results suggest athletes within the normal BMI category experience a diminished response to 4000 IU d⁻¹ of vitamin D₃ supplementation, and periods of high bone turnover may be an additional risk factor for developing compromised vitamin D status in athletes.