Vitamin D Supplementation Does Not Enhance Gains in Muscle Strength and Lean Body Mass or Influence Cardiorespiratory Fitness in Vitamin D-Insufficient Middle-Aged Men Engaged in Resistance Training

Background: This study checked whether vitamin D (Vit-D) supplementation improves the efficacy of resistance training (RT) in terms of increasing muscle strength and lean body mass (LBM), and influencing cardiorespiratory fitness (VO2max) in Vit-D-deficient middle-aged healthy men. Methods: Participants (n = 28) were quasi-randomly assigned to one of two groups, which, in a double-blind manner, supplemented their diet daily with either Vit-D (8000 IU; VD) or placebo (PLC) during participation in a 12-week supervised RT program. Results: During the intervention, serum Vit-D concentrations increased 2.6-fold (p < 0.001) in the VD group, while no changes occurred in the PLC group. Muscle strength gains (p < 0.001) as measured in seven exercises performed on RT equipment and increases (p < 0.001) in LBM were similar in the two groups. Total fat mass, percent total fat, and percent android fat decreased (p < 0.05) to a similar extent in both groups, but there was no change in VO2max in either group. Conclusions: In conclusion, in healthy Vit-D-insufficient middle-aged men engaged in resistance training, Vit-D supplementation increases serum 25(OH)D levels but does not enhance gains in muscle strength and LBM, or decreases in fat mass and fat percentage, and does not affect cardiorespiratory fitness.