Can Vitamin D improve your aerobic fitness?

vitamin d supplements

Vitamin D is important for your health, especially as an endurance athlete - it’s essential to keep your bones and muscles functioning as they should be. But now, there may be another reason to make sure your levels are optimal: researchers from Virginia Commonwealth University have now found a link between vitamin D and cardiorespiratory fitness (CRF).

In the study, which was published in the European Journal of Preventive Cardiology, researchers tested the blood of nearly 2,000 participants to determine their vitamin D levels, and compared those to their V02 max—a marker of cardiorespiratory fitness, since it shows how efficiently your body uses oxygen. Then, they split the participants into quartiles based on their levels of D.

Related: The only supplement runnes need to take

The researchers discovered that participants in the highest quartile of vitamin D levels had significantly higher VO2 max levels than those in the lowest quartile, suggesting that their cardiorespiratory fitness was higher, too.

Previous research suggests that vitamin D may increase the numbers of one type of fast-twitch muscle fibers and decrease another, leading to improved aerobic fitness.

Still, the researchers aren’t able to say whether higher levels of D actually caused an improvement in aerobic fitness.

“There is an association between vitamin D and CRF, but we don’t know if the CRF is better because of higher vitamin D levels, or if vitamin D levels are better because of higher CRF,” study author Amr Marawan, M.D., told Runner’s World.

Plus, it’s not exactly clear whether increasing or supplementing with D will help your aerobic fitness if your levels are already in the normal range and you aren’t deficient in it—there’s been conflicting data on that, Marawan said.

More research needs to be done before any recommendations about supplementing for improved cardio fitness can be made. In the meantime, you can look to natural sources of it—think egg yolks and fatty fish—to make sure you’re getting enough to maintain general wellness. You can also ask your doctor about taking a vitamin D blood test to check if your levels are normal.

A version of this article appeared on Runner's World US