Vitamin D supplementation does not enhance resistance training-induced gains in muscle strength and lean body mass in vitamin D deficient young men

Purpose Vitamin D (Vit-D) supplementation has been shown to increased muscle strength in young adults. It remains unclear if Vit-D supplementation enhances the efficacy of resistance training (RT). This study tested the hypothesis that Vit-D supplementation would enhance the RT-induced increases in muscle strength and lean body mass (LBM) in Vit-D deficient young men. Methods Thirty-nine men (baseline serum 25(OH)D < 50 nmol L ‒1 ) were quasi-randomly assigned to one of the two groups that performed a 12-week supervised RT program concomitant with either Vit-D (8000 IU daily; VD) or placebo (PLC) supplementation. Results During 12-week RT, energy and nutrient (except Vit-D) intake and training loads did not differ in the two groups. Serum 25(OH)D levels increased from 36.3 ± 9.2 to 142.4 ± 21.9 nmol L ‒1 ( P < 0.05) in VD group and remained unchanged between 36.3 ± 8.9 and 29.4 ± 6.6 nmol L ‒1 ( P > 0.05) in PLC group. Muscle strength (1-repetition maximum) increased ( P < 0.05) to an equal extent in the two groups in 5 exercises performed on RT equipment, whereas strength gains in chest press and seated row were greater ( P < 0.05) in PLC compared to VD group. Total and regional LBM (measured by DXA scan) increased ( P < 0.05) equally in the two groups. Android fat mass decreased ( P < 0.05) in VD group only. Conclusion Vit-D supplementation does not enhance the efficacy of RT in terms of muscle strength and LBM gains in Vit-D deficient young healthy men.