Vitamin D has been linked to performance but as discussed in this vitamin D supplementation guide, there is currently insufficient evidence to conclude that vitamin D is a direct performance enhancer. This is partly because of a lack of well controlled and large enough studies. But a recent publication (to be published soon) from the team of Professor Neil Walsh at Bangor University in Wales addressed in 2 studies: In the first one, the relationship between vitamin D status and a fairly large (almost 1000) number of men and women was studied. The second study provided safe simulated sunlight or vitamin D3 supplements to see if performance improvements could be achieved.
In the first study all 967 participants completed a 1.5 mile run and maximum dynamic lift as well as explosive power was assessed. All participants also gave blood for 25[OH]D analysis and it was found that during winter only 9% of men and 36% of women were vitamin D sufficient. When the researchers then correlated vitamin D status with performance measures they found that there was a correlation between vitamin D status and endurance performance. This effect was present in both men and women. Vitamin D status explained about 5% of the variation in performance. Every 1 nmol/L increase in 25[OH]D resulted in a 0.42 sec faster 1.5 mile run. There were no such correlations with maximum dynamic lift or explosive power.
In the second study, 137 men received simulated sunlight or vitamin D3 supplements, a placebo supplement or placebo simulated light. Both treatments (sunlight and supplements) were effective in achieving vitamin D sufficiency (in 97% of all participants). However, performance was not affected by the supplementation. The authors discuss that perhaps the duration of supplementation (12 weeks) was not enough to see significant effects.
This new publication adds to the literature and provides some interesting new data. The authors also acknowledge that there are some limitations. For example, in study 1 where correlations were observed it is not possible to determine what is cause and what is effect. It is possible that higher vitamin D levels may improve performance. However, it is also possible that those with better performance spend more time in the sun and have better vitamin D status.
As a practical message, the authors suggest that supplementation should start before the start of the winter season to prevent the decline, rather than trying to repair a deficiency.
As soon as the link to the full study becomes available we will update this here.