Abstract

We investigated the seasonal variation in serum vitamin D (25(OH)D) in elite athletes and the effectiveness of vitamin D3 supplementation. 20 athletes comprising the British Modern Pentathlon squad were included. Blood samples for investigation of 25(OH)D were collected in beginning of Oct., end of Feb., and June. From October 2009 to February 2010 the athletes did not receive vitamin D supplements (observation period). However, for winter 2010–11 season, athletes were supplemented with 50,000 IU of D3 per month from November 2010 to March 2011 (supplementation period). Vitamin D3 supplements were from Biotech Pharmacal Inc, USA. Venous blood samples were drawn for analysis of 25(OH)D by chemiluminescence assay for total serum 25 (OH)D. Data are represented as mean (SD). Differences between means were compared using two-sample t-test. Level of significance was set at p<0.05. The mean squad 25(OH)D for the observation period was 98±18 nmol.l⁻¹, 76±21 nmol.l⁻¹ and 118±15 nmol.l⁻¹ for Oct. 2009, Feb. 2010 and June 2010 respectively. For the supplementation period, mean 25(OH)D was 90±20 nmol.l⁻¹ and 104±19 nmol.l-¹, for Oct. 2010 and Feb. 2011. The vitamin D supplementation period was effective at elevating the squad 25(OH)D, as the Feb. 2011 result of 104±19 nmol.l⁻¹ was greater than the Feb. 2010 result of 76±21 nmol.l⁻¹ with no supplementation (p<0.01). Supplementation was effective at elevating the squad 25(OH)D; as 6% (n=1) of the squad presented with a 25(OH)D concentration of <80 nmol.l⁻¹ in Feb.2011. In contrast, the winter period with no supplementation, 56% of the squad had 25(OH)D concentrations of <80 nmol.l⁻¹, and 19% had 25(OH)D concentrations of <50 nmol.l⁻¹ in Feb.2010. Supplementation with 50,000 IU of vitamin D3 per month across the winter is effective in caucasian athletes in maintaining 25(OH)D >80 nmol.l⁻¹; as long as 25(OH)D concentrations are >80 nmol.l⁻¹ at the time of commencing supplementation.