Vitamin D affects your muscles, immune system, and energy levels, so it will probably also have an effect on your performance. In a new study in PLOS One, researchers wanted to see whether vitamin D levels in athletes were associated with strength and other measures of fitness. 



Previous studies have found that even in athletes who live in regions with plenty of sunlight (a major source of vitamin D in humans), vitamin D levels are often low. The goal of this new study was to take a look at both the vitamin D status and performance levels of a group of elite athletes, in this case soccer players.


Study Design

Breaking Muscle Shop

67 Caucasian soccer players participated in this study. The Caucasian part is important, because lighter skin has fewer defenses against the sun and will produce more vitamin D when exposed to light. While the results will still be true for darker-skinned people, they may have to spend more time outdoors or in brighter sunlight to attain the same vitamin D status as Caucasian athletes.


The athletes were tested twice - once before the start of the study and again after the end of their six-week off-season period. Blood was drawn and a host of performance tests were levied, including jumps, sprints, and VO2 max testing. At the start of the off-season, about half of the players had insufficient levels of vitamin D, despite spending a lot of time outside.



Vitamin D correlated significantly with every performance variable studied. Power, speed, and cardiovascular ability all responded positively to high vitamin D levels both times the athletes were tested.


Interestingly, vitamin D levels increased from the first test to the second one. This indicates that vitamin D levels seem to be lower during intense training, since the first test was taken at the end of their season. Presumably, vitamin D is used more readily during training, which would explain why the levels were lower in the first test. Also, the off-season period was in the summer time, allowing the athletes to get out of their uniforms and spend more time outdoors.


Performance levels, on the other hand, were lower during the second test, when vitamin D levels were the highest. These results may seem contradictory, but the explanation is simple. Since it was the off-season, the athletes trained much less and their performance went down, despite the relatively high vitamin D levels.


Ultimately, the researchers stated that training plays the central role in determining performance. But we can’t forget the factors that play a supporting role, and which can make or break high-level performance. Vitamin D is one of these factors. Without getting a sunburn, ensure that you are spending time in the sun with your skin exposed and supplement as needed.



1. Nikolaos Koundourakis, et. al., “Vitamin D and Exercise Performance in Professional Soccer Players,” PLOS ONE 2014, 9:7


Photo courtesy of Shutterstock.

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