Vitamin D insufficiency and deficiency are well-documented in populations living north or south of approximately 35° N or S latitude, respectively; these are even more pronounced during winter months. Athletes have been shown to be more susceptible to insufficiency and deficiency than non-athletes. Vitamin D has been linked to mental cognition. Winter-sports athletes residing in the circumpolar north may experience sub-optimal vitamin D levels and depressed cognitive abilities during the competitive season. PURPOSE: To determine if significant differences of vitamin D concentrations and manual dexterity exist in winter athletes mid- and post-season in the circumpolar North. METHODS: Fifteen competitive cross country skiers residing at 64° N were recruited for this study. Blood samples were taken in early February (“mid-season”) and in late April (“post-season”). Subjects completed the Purdue Pegboard Test (PPT), a timed multi-test assessment of mental cognition and manual dexterity, at the time of the blood draws. Plasma vitamin D concentration was measured as 25-hydroxyvitamin D [25(OHD)] using an ELISA. Significance was determined by permutation test with 95% confidence interval. RESULTS: Subjects exhibited significantly lower mean concentration of plasma 25(OH)D in post-season (± 3.39 ng/mL, SD=4.53) as compared to mid-season (± 5.94, SD=3.37). Subjects exhibited significantly higher PPT scores in three of four tests in post-season (± 18.00, SD=1.31; ± 16.89, SD=1.12; ± 46.64, SD=3.40) versus mid-season (± 17.04, SD=1.82; ± 15.98, SD=1.62; ± 41.69, SD=4.37) with no significant differences in the remaining test. CONCLUSION: Post-season mean plasma 25(OH)D concentration was significantly lower than mid-season. This could be explained by significantly reduced intake of vitamin D supplements post-season. PPT scores improved significantly in two of four tests in the post-season suggesting that 25(OH)D may not necessarily be linked to cognitive function measured with PPT. However, mean 25(OH)D concentrations from both mid- and post-season fell below the Institute of Medicine’s definition of “deficient” suggesting that subjects’ improvement on PPT may have been attributable to another factor or factors such as reduced stress levels.

Supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Numbers UL1GM118991, TL4GM118992, or RL5GM118990.

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