Study Finds Vitamin D Helps Maintain Immune Health, but Does Not Improve Running Performance

​A new winter-long study suggests that while vitamin D supplements can help maintain healthy vitamin levels and support immune markers, they do not appear to improve athletic performance in runners.

​Researchers tracked 45 healthy adults from October to March, a period when sunlight exposure is low and vitamin D levels typically decline.

​Participants were divided into four groups: runners taking vitamin D supplements, runners without supplements, non-runners taking supplements, and non-runners without supplements.

​Those in the supplement groups received 2,000 IU of vitamin D3 per day for eight weeks using dissolvable strips. After the supplementation period ended, researchers continued to monitor the participants for another 12 weeks to observe how vitamin D levels changed during the rest of the winter.

​Blood tests showed that vitamin D levels increased significantly in participants who took the supplement.

​Supplemented runners saw their vitamin D levels rise by about 21%, while supplemented non-runners experienced an increase of nearly 29%.

​Participants who did not take supplements saw their levels fall during the winter months. The drop was particularly noticeable in non-runners.

​However, once supplementation stopped, vitamin D levels declined again across all groups by March.

​Performance tests showed little difference between groups. VO₂max, explosive power, and strength remained largely unchanged throughout the study.

​Researchers say the results suggest vitamin D may help maintain health during winter, but it should not be considered a performance enhancer.