Last time, we reviewed how your calcium intake can affect your bone health, and in doing so, we noted that vitamin D, which boosts calcium absorption, can impact the strength of your bones too. Today, we’ll be taking a closer look at vitamin D itself, as it is a very unique nutrient.
While a vitamin by name, vitamin D is, in truth, a hormone with multiple chemical variants. Also, unlike other dietary vitamins, your body is capable of synthesizing vitamin D internally in your skin by using ultraviolet light (most often from the sun) and precursor chemicals related to cholesterol, present in your body in abundant quantities.
Vitamin D is also rare in foods, with the notable exceptions of mushrooms (which also synthesize their vitamin D using sunlight) and fish oil. Ultimately, most people get the majority of their vitamin D via synthesizing it in their body with sunlight.
Since many people across the country and the world live in areas that are sun-starved for much of the year, scientists have discovered that a large proportion of people have some form of vitamin D deficiency.
One recent study of teenagers in Massachusetts found that about one in four are deficient in vitamin D, and that low levels of the vitamin are more common in the winter and in those with darker skin (who need more sunlight to synthesize vitamin D).
Does vitamin D affect athletic performance?
- A 2008 review study by John Cannell and collaborators cites a study of Finnish gymnasts and runners, which found that an astounding 67% were deficient in vitamin D—though these results could have been skewed by the gymnasts, who train and practice mostly inside.
- Another study conducted in 2010 involving collegiate athletes at the University of Wyoming found that the number of athletes with healthy levels of vitamin D dropped from 76% in the fall to 15% in the winter.
- Additionally, the athletes with higher levels of vitamin D were less likely to get sick. In a review article authored by two of the scientists from the University of Wyoming study, Willis and Larson-Meyer argue that, given the emerging connection between low vitamin D levels and chronic inflammatory and autoimmune diseases in elderly people, we ought to be concerned about vitamin D levels in athletes.
- Low vitamin D levels could perhaps also lead to illness or injury in athletes by influencing immune and inflammatory reactions, according to Willis and Larson-Meyer. These concerns were expounded on by Willis and Larson-Meyer in a longer review article, which cited studies which found vitamin D deficiency in a large proportion of patients at an inner-city clinic who complained of vague muscular pains or fatigue.
- Another study they cite found that supplementation with vitamin D3 resulted in improvements in back pain—though any study on back pain treatments ought to be approached with caution, as most cases resolve spontaneously.
Vitamin D supplementation for athletes
For athletes at northern latitudes, especially those with darker skin or who train and compete indoors, Willis and Larson-Meyer recommend exposure to the sun, if possible, for 5-30 minutes during the middle of the day, or taking a vitamin D supplement which provides 1000-2000 IU of vitamin D3 per day.
Other studies have used somewhat higher dosages with no apparent ill effects. They emphasize caution with sun exposure, since it can increase your risk of skin cancer when done excessively.
Vitamin D and athletic performance
When it comes to actual performance, there are unfortunately no solid studies as of yet that have directly looked at whether athletes with low vitamin D levels perform worse than those with healthy levels, or whether vitamin D supplements can boost performance.
Cannell et al., however, cite a fascinating series of papers from the 1930s to 1950s, originally published in Germany, which found that sun-like ultraviolet light exposure over several weeks had a consistent, positive impact on the athletic performance of the studies’ subjects, in tasks ranging from the 100m dash to physical fitness tests in schoolchildren.
The most plausible explanation for this boost in performance, according to the authors, is increased synthesis of vitamin D by the body as a result of the ultraviolet light exposure.
Additionally, seasonal performance, as measured by muscular strength increases relative to a standardized training program, seems to peak along with blood levels of vitamin D, which vary throughout the year due to sun exposure. This peak appears to occur in late August and September, with vitamin D levels and muscular training response both dropping sharply by November.
Final thoughts on vitamin D
The complexities of vitamin D in the body are a relatively new discovery. Given this, it shouldn’t be too surprising that studies are lacking on its effect on athletic performance.
There is a swelling body of evidence that connects low vitamin D levels with both acute and chronic illnesses, as well as general malaise in sedentary people, but high-quality modern studies on athletes and their performance are critically lacking. Until they are published, the most we can say is that there is some circumstantial evidence that vitamin D can have an impact on performance by influencing your overall health and recovery.
If there is a deleterious effect to having low vitamin D levels, these people are mostly at risk:
- People with dark skin
- People who live further away from the equator
- People who spend little time outdoors
The guidelines for maintaining optimal vitamin D levels that are presented in the studies we looked over are:
- Large areas of skin exposure to full sunlight for 5-30 minutes several times per week (dependent on the season, your skin tone, etc.) and
- Supplemental vitamin D with dosages ranging from 1000 IU to 5000 IU per day.
As the science evolves, these guidelines will probably become more clearer as will the role of vitamin D in overall health and athletic performance.
