Impaired muscle function has been coupled to vitamin D insufficiency in young women and in elderly men and women. Those living at Northern latitudes are at risk for vitamin D insufficiency due to low sun exposure which may be more pronounced among elite swimmers because of their indoor training schedules. We aimed to examine vitamin D status among young elite swimmers and evaluate the association between vitamin D status and muscle strength. Twenty-nine swimmers, 12 female and 17 male (16–24 years) residing at latitude 55–56°N were studied in March and April. Blood samples were analyzed for serum 25-hydroxyvitamin D (s-25(OH)D) and hand-grip strength was measured as marker of muscle strength. Subjects´ vitamin D and calcium intake were assessed by food frequency questionnaire and sun exposure and training status by questionnaires. Mean (± SD) s-25(OH)D was 52.6 ± 18.3nmol/L among all swimmers. In 45% of the swimmers s-25(OH)D was below 50 nmol/L. Female swimmers had higher s-25(OH)D concentration than male swimmers (61.7 ± 17,5 nmol/L vs. 46.2 ± 16,5 nmol/L, p = .026). Among male swimmers, those with sufficient vitamin D status had higher hand grip strength than those with insufficient vitamin D status (50.6 ± 6.4 kg vs. 41.1 ± 7.8 kg, p = .02). Among Danish elite swimmers 45% had an insufficient vitamin D status during the spring; the prevalence being higher among male swimmers. Muscle strength was significantly higher in male swimmers with sufficient vitamin D status.
Geiker is with the Clinical Nutrition Research Unit, Copenhagen University Hospital Herlev and Gentofte, Hellerup, Denmark. Larsen and Kristensen are with the Dept. of Nutrition and Health, Metropolitan University College, Copenhagen K, Denmark. M. Hansen is with the Dept. of Public Health—Sport Science, University of Aarhus, Aarhus, Denmark. Jørgensen is with the Dept. of Clinical Biochemistry, Rigshospitalet, Glostrup, Denmark, and OPEN, Odense Patient data Explorative Network, Odense University Hospital/Institute of Clinical Research, University of Southern Denmark, Odense, Denmark. Jakobsen is with the National Food Institute, Technical University of Denmark, Søborg, Denmark. B.S. Hansen is with the The Municipality of Frederiksberg, Frederiksberg, Denmark. Bügel is with the Dept. of Nutrition, Exercise and Sports, University of Copenhagen, Frederiksberg C, Denmark.