Does vitamin D supplementation augment exercise-induced changes in health and physical performance?

The purpose of this research was to examine the effects of vitamin D supplementation (4000 IU/d) during an exercise training intervention on body composition, muscular strength and power, glucose tolerance, and inflammatory biomarkers. Twenty-three (26.1 ± 4.7 yrs) overweight-to-obese (BMI: 31.3 ± 3.2 kg/m2) adults were recruited during winter months (25-hydroxyvitamin D (25OHD) 19.3 ± 7.2 ng/mL) and randomized into a vitamin D (VitD, n = 10) or placebo (PL, n = 13) group. Both groups completed 12 wks (3 d/wk) of resistance exercise training and were asked to use sunscreen daily. At 0 and 12 wks, a 2-h 75-g oral glucose tolerance test was performed and vitamin D status (25OHD), parathyroid hormone (PTH), body composition (DXA), inflammatory biomarkers (C-reactive protein (CRP), tumor necrosis factor alpha (TNFα), interleukin 6 (IL-6), and LPS-stimulated TNFα), and indices of liver function (alanine aminotransferase (ALT)), were assessed. Muscular strength and power were measured at baseline, 4, 8, and 12 wks. At 12 wks 25OHD levels (33.4 ± 7.2 ng/mL) in VitD were increased compared to baseline (20.8 ± 8.3 ng/mL) and significantly elevated compared to PL (23.5 ± 6.0 ng/mL). At 12 wks PTH levels were significantly decreased in the VitD group only, compared to baseline. Peak power increased at 4 wks in the VitD group (16.7 %, p\u3c0.05) only, and the change in peak power (at 4 wks) from baseline was significantly higher in VitD compared to PL; but at 8 and 12 wks, peak power was not different between groups. Lean mass and muscular strength at 12 wks were increased in both groups (p\u3c0.05) compared to baseline, but no differences were detected between groups. No differences, within or between groups at 0 and 12 wks were detected for fasting glucose, fasting insulin, 2-h post-load glucose, area under the glucose curve, and homeostasis model assessment of insulin resistance. No significant differences between groups were found for the absolute change (from baseline) in CRP (PL: -0.3 ± 2.6 mg/L; VitD: 2.2 ± 4.5 mg/L), TNFα (PL: 0.2 ± 0.9 pg/mL; VitD: -0.5 ± 0.9 pg/mL), IL-6 (PL: 0.1 ± 0.7 pg/mL; VitD: 0.0 ± 0.5 pg/mL), and LPS-stimulated TNFα. Further, no differences within or between groups at 0 and 12 wks were detected for serum ALT. Vitamin D supplementation during exercise training induced an early increase in peak power, but did not augment improvements in lean mass or muscular strength. The intervention prescribed for both groups had no influence on glucose tolerance, inflammatory biomarkers (CRP, TNFα, and IL-6), LPS-stimulated TNFα production, and indices of liver function. Additional research is necessary to further understand the effects of vitamin D supplementation during a period of exercise training