Metabolism of vitamin D is not affected by sport activity

Higher levels of physical activity are related to higher 25-(OH)D levels. Total 25-(OH)D (25-(OH)D_T) are routinely used in clinical practice to assess vitamin D, however novel biomarkers are currently being investigated as free 25-(OH)D (25-(OH)D_F) or vitamin D metabolite ratios (VMRs). The primary aim of our study was to assess 25-(OH)D_F, vitamin D metabolites and VMRs in inactive men and athletes. A secondary aim was to check whether regular physical activity influence on vitamin D metabolome. A tertiary aim was to determine the relationship between 25-(OH)D_T, 25-(OH)D_F, vitamin D binding protein (VDBP), vitamin D metabolites and VMRs in this cohort.

A total of 69 participants (27 inactive men, 18 indoor and 24 outdoor athletes) participated in the study. Vitamin D metabolites (25-(OH)D_T, 24,25-(OH)₂D₃, 3-epi-25-(OH)D₃, and 1,25-(OH)₂D) were assessed using LC-MS/MS. The 25-(OH)D_F concentration was calculated based on serum albumin and VDBP levels.

There were no differences in vitamin D metabolites and VMRs between inactive men and between the two groups of athletes. We showed a strong relationship between 25-(OH)D_T, 25-(OH)D_F and 24,25-(OH)D₃, 3-epi-25(OH)D₃, 24,25-(OH)₂D₃:25-(OH)D_3 VMR in each group. Analysis showed that 25-(OH)D_T, 25-(OH)D_F inversely associated with 25-(OH)D₃:24,25-(OH)₂D₃, 25-(OH)D₃:3-epi-25-(OH)D_3, 1,25-(OH)₂D:24,25-(OH)₂D₃ ratios in inactive men and athletes (indoor and outdoor).

On the basis of our results, we concluded that regular long-term physical activity has no effect on the concentration of vitamin D metabolites at rest. Furthermore, free vitamin D does not correlate more strongly with vitamin D metabolites and VMRs compared to total.