Acute Effects of a Single Bout of Strength and Endurance Exercise on Vitamin D Metabolites in Young Adults.

Purpose: The effect of exercise on serum concentration of vitamin D metabolites remains inconclusive, with studies reporting deviating results. This study evaluated the acute effect of a single session of two specific exercise forms; strength training (ST) and high-intensity interval training (HIIT), on circulating 25-hydroxyvitamin D (25(OH)D), free 25(OH)D and 1,25-dihydroxyvitamin D (1,25(OH) 2 D), and skeletal muscle vitamin D receptor (VDR) gene expression, in healthy adults.

Methods: Thirty-nine participants (19 women and 20 men, aged 21-30 yr) completed a single bout of ST and HIIT exercise, separated by 2 weeks. Serum concentration of total 25(OH)D, free 25(OH)D and 1,25(OH) 2 D were assessed before exercise, immediately after, and 3 and 24 h after each session. Muscle biopsies were obtained at rest (first visit), and at 3 and 24 h post ST and HIIT, and analyzed for VDR gene expression. Repeated-measures ANOVA was used to assess serum concentration across time, whereas a one-way ANOVA was used for muscle VDR gene expression analyses.

Results: Serum concentration of 25(OH)D or free 25(OH)D did not change after either exercise mode when correcting for plasma volume alterations. 1,25(OH) 2 D was reduced by 13.1 ± 18.3 pmol·L -1 and 7.1 ± 9.6 pmol·L -1 immediately after ST and HIIT, respectively ( P < 0.001). Muscle VDR mRNA expression increased after ST by 3.1 ± 1.8 (3 h) and 2.2 ± 1.7 (24 h) fold change ( P < 0.05).

Conclusions: One single session of ST or HIIT did not alter serum concentration of 25(OH)D and free 25(OH)D when correcting for plasma volume changes. Both exercise modes caused a transient reduction in 1,25(OH) 2 D suggesting utilization of 1,25(OH) 2 D by muscle cells after exercise. Elevated VDR gene expression after ST suggests a functional role of VDR in fast-twitch muscle fibers.