Previously we’ve told you about how vitamin D can benefit athletic performance.

A newer study shows us how vitamin D is related to respiratory infections in endurance athletes.

In this study, researchers evaluated 225 endurance athletes over the course of a 16-week winter training period. They measured plasma levels of vitamin D and a specific anti-microbial protein called cathelicidin at the start of the study.

They found that plasma cathelicidin concentration correlated with the plasma vitamin D concentration, meaning that vitamin D levels had an influence on the production of this specific protein that kills bacteria. The researchers also found that low vitamin D levels were associated with increased upper respiratory infections.

In another part of the study, researchers also found that secretion of an important immune system chemical (secretory immunoglobulin A (IgA)  - which plays a big role in immune function in the mouth and gut – was significantly higher in the athletes with optimal vitamin D levels.

Endurance athletes tend to suffer from more than their fair share of upper respiratory infections, in part because excessive exercise can weaken immunity.

38 percent of the athletes had insufficient or deficient vitamin D levels at the start of the study, and by the end of the study, 55 percent had insufficient or deficient levels. Also, they found that a significantly greater number of subjects who presented with symptoms of an upper respiratory tract illness had deficient levels of vitamin D than optimal levels of vitamin D.

The study authors stated, “Low vitamin D status could be an important determinant of upper respiratory tract illness risk in endurance athletes.”

So, what is an optimal vitamin D level?  Most laboratory reference ranges put that number right around 30, with anything below as insufficient.

However, we would argue that just because one isn’t ‘insufficient’, does not mean that they have optimal levels.

An ideal blood level of vitamin D is actually closer to 50 and above.  It’s always a good idea to get your levels measured, especially if you tend to suffer from more respiratory infections during the winter.

Reference:

He CS, et al. Exerc Immunol Rev. 2013;19:86-101.