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), free25(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, age 21-30 years) completed a single bout of ST and HIIT exercise, separated by two weeks. Serum concentration of total 25(OH)D, free25(OH)D and 1,25(OH)2D were assessed before exercise, immediately after, and 3 hours and 24 hours after each session. Muscle biopsies were obtained at rest (1st visit), and at 3 hours and 24 hours post ST and HIIT, and analyzed for VDR gene expression. Repeated measures ANOVA was used to assess serum concentration across time, while paired samples t-test 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 and 7.1 ± 9.6 pmol/L immediately after ST and HIIT, respectively (P < 0.001). Muscle VDR mRNA expression increased after ST by 3.1 ± 1.8 (3 hr) and 2.2 ± 1.7 (24 hr) 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 following exercise. Elevated VDR gene expression following ST suggests a functional role of VDR in fast-twitch muscle fibers.
Copyright © 2025 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.