Investigation of the relationship between body composition, muscle strength, plasma vitamin D and some hormone levels in national athletes performing jump

Vitamin D, a vital nutrient, exerts important physiological effects on bone mineralization, muscle function, cellular growth, immune response and glucose metabolism. Recently, vitamin D insufficiency and/or deficiency has reached epidemic proportions and has been linked to several health problems such as low bone mineral density, muscle weakness, cancer and obesity in adults. Some hormones such as cortisol, TSH, T4 and testosterone have also important effects on athletic performance and body composition. The objective of the present study was to examine the relationship between plasma 25-hydroxyvitamin D [25(OH)D3] and hormone levels, muscle strength, anthropometric parameters and nutritional profile in national young athletes. Twenty male and six female athletes (15-25 years) performing jumping events in Turkish national team were included in the study. Athletic performances of the participants were evaluated by using several jump tests such as drop jump, vertical jump, squat jump, standing long jump, and free arm jump. Anaerobic power (watt) was calculated by using Lewis nomogram for each participant. Body composition of each participant was estimated from skinfold thickness using a skinfold caliper. The skinfold measurement was performed at seven sites (chest, abdominal, triceps, suprailiac, midaxillary, subscapular and thigh) according to standard protocols. Body fat percentage was calculated according to Jackson/Pollock 7 method. Plasma 25(OH)D3 and other hormone levels were detected by using ELISA kits according to the manufacturer's instructions. Also, athletes were completed a detailed questionnaire relating to their lifestyle, nutritional profile and sun exposure practices. Statistical analysis was performed using SPSS 18.0. Spearman's correlation test was used to analyze the relationship between the dependent and independent variables. A p value ≤ 0.05 was considered statistically significant. According to our results, the rate of vitamin D insufficiency and/or deficiency was 66% in females and 45% in males. No significant relationship was found between the plasma 25(OH)D3 levels and performance measures. However, there was a significant negative correlation between the plasma 25(OH)D3 levels and antropometric parameters (chest, abdominal, triceps and suprailiac skinfold thickness) and body fat percentage (p<0.005) in females but not in males. Also, significant correlations were found between the athletic and antropometric parameters and hormone levels both in female and male athletes. Overall, these findings indicate a high prevalence of vitamin D insufficiency and/or deficiency in elite athletes. Furthermore, an inverse correlation between plasma 25(OH)D3 levels and body fat percentage suggest that athletes with a excess adiposity may be at higher risk for vitamin D insufficiency. In addition, our results suggested that cortisol, testosterone and thyroid hormones might have significant effects on athletic performance and body composition.