The location of physical activity determines its efficacy on Vitamin D status: Evidence from a meta-analysis

Background: Numerous epidemiological studies have identified a positive correlation between increased physical activity and raised levels of serum 25-hydroxyvitamin D (25(OH)D). However, it remains uncertain whether this correlation implies a cause-and-effect relationship. The aim of this systematic review and meta-analysis was to analyze the effects of physical activity on serum 25(OH)D concentrations in humans. Materials and Methods: Interventional studies examining the effect of physical activity on serum 25(OH)D and published before July 2025 were detected by searching online databases, including PubMed, Embase, Scopus, and Web of Sciences, using a combination of suitable keywords. The heterogeneity among the included trials was evaluated using I 2 statistics. Data were pooled using a random-effects model, and the weighted mean difference (WMD) was considered as the overall effect size. Results: Thirty eligible studies were included in the final analysis. Pooling effect sizes from studies demonstrated a significant increase in serum 25(OH)D levels following physical activity (WMD = 4.08 nmol/L; 95% confidence interval [CI]: 2.05, 6.11). Moreover, in subgroup analysis, the outdoor setting of the intervention resulted in a large and statistically significant difference in the serum Vitamin D levels, compared to the control groups (WMD: 17.23 nmol/L, 95% CI: 14.54, 19.92). However, the indoor setting of the physical activity intervention had a negligible effect on the serum Vitamin D levels (WMD: 0.37 nmol/L, 95% CI: −0.38, 1.14), compared to the control groups. Conclusion: These results propose that prescribing outdoor physical activity may be an effective clinical strategy for improving Vitamin D levels, primarily mediated through sunlight exposure.