Background: Higher levels of physical activity and cardiorespiratory fitness are positively related to serum 25-hydroxyvitamin D [25(OH)D] concentrations; however, the response of 25(OH)D concentrations to chronic endurance exercise training is unclear. Therefore, the purpose of this study was to elucidate whether serum 25(OH)D concentrations were directly increased by 5 weeks of endurance exercise training and influenced by changes in body fat in elderly men. Methods: Twenty elderly Japanese men were randomized to either the 5-week endurance exercise training group (ET group; N = 10) or the sedentary control group (SC group; N = 10). Fasting blood samples were collected to determine serum 25(OH)D and other blood parameters. The visceral fat area and hepatic fat content were assessed by magnetic resonance imaging and proton magnetic resonance spectroscopy, respectively. Results: After 5 weeks of endurance exercise training, the levels of maximal oxygen uptake (VO2 max) were significantly increased from 23.3 at baseline to 28.1 mL/kg/min at the endpoint for the ET group; levels were unchanged for the SC group. A significant seasonal reduction in serum 25(OH)D concentrations was observed in the SC group (P < 0.05), while no change was found in the ET group. The results may be partly attributed to the slight decrease in intrahepatic fat in the ET group. No changes were observed in percent body fat or visceral fat area. Conclusions: The results of our study suggest that 5 weeks of endurance training could inhibit the seasonal reduction in serum 25(OH)D concentrations without changes in body fat.
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