Seasonal variation of vitamin D levels in Swiss athletes

Abstract

Introduction: Vitamin D deficiency is very prevalent in world population and growing evidence shows that also athletes are affected. Vitamin D deficiency causes beside bone disorders, musculoskeletal pain, muscle weakness and is associated with many other health disorders. For athletes in particular it may impair training and performance, prolong recovery and increase risk of injury. We therefore analyzed vitamin D levels in Swiss athletes focusing on prevalence according to age, gender, seasonal variations, indoor or outdoor sports, sunscreen use and vitamin D supplementation. Methods: This study was performed in a convenient sample of 655 Swiss Olympic athletes over one year. Blood samples were obtained and a questionnaire was filled in at Swiss Olympic Medical Centers or Bases during an annual routine exam. Data were then sent to the central laboratory of the Aarau hospital where they were processed and sent to us in an anonymized version. Vitamin D levels were categorized into deficiency (≤ 50 nmol/l), insufficiency (between 50 and 75 nmol/l) and adequate levels (> 75 nmol/l) of 25-hydroxyvitamin D. By means of the questionnaire, we assessed age, gender, type of sport, symptoms possibly related to vitamin D deficiency during the last year, frequency of sunscreen use and vitamin D-containing medications of the athletes. Results: 13.5% of the participants (total number = 651) presented a vitamin D deficiency, 37.8% a vitamin D insufficiency so that more than half of the athletes (51.2%) had inadequate vitamin D levels. Inadequate vitamin D levels were more prevalent in younger athletes, during seasons with lower sun exposure, in indoor sports during the sun deprived seasons, in athletes without vitamines supplementation and in athletes of lower Swiss Olympic classes compared to their counterparts. Conclusions: The results of the study show that the prevalence of inadequate vitamin D levels in Swiss athletes is substantial for younger athletes (< 18 years of age) and for indoor athletes during sun deprived periods of the year. However, a general vitamin supplementation containing vitamin D reduced the prevalence of vitamin D inadequacy which is especially relevant during sun deprived seasons.