Seasonal variation in vitamin D status in elite athletes: a longitudinal study

Studies monitoring vitamin D status in athletes are seldom conducted for a period of 12 months or longer, thereby lacking insight into seasonal fluctuations. The objective of the cur-rent study was to identify seasonal changes in total 25-hydroxyvitamin D (25(OH)D) concen-tration throughout the year. Fifty-two, mainly Caucasian athletes with a sufficient 25(OH)D concentration (>75 nmol/L) in June were included in this study. Serum 25(OH)D concentra-tion was measured every three months (June, September, December, March, June). Addition-ally, vitamin D intake and sun exposure were assessed by questionnaires at the same time points. Highest total 25(OH)D concentrations were found at the end of summer (113±26 nmol/L), whereas lowest concentrations were observed at the end of winter (78±30 nmol/L). Although all athletes had a sufficient 25(OH)D concentration at the start of the study, nearly 20% of the athletes were deficient (<50 nmol/L) in late winter.