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

Abstract

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)2D), 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)2D 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)2D 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)2D suggesting utilization of 1,25(OH)2D by muscle cells after exercise. Elevated VDR gene expression after ST suggests a functional role of VDR in fast-twitch muscle fibers.