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Vitamin D is one of the most well-researched and popular supplements in the world (at the time of this posting, it has over 60,800,000 google hits).

If you scour the web you will find that vitamin D apparently cures cancer and solves world hunger simultaneously (that is a bunch of malarky).

Yet despite this, its effects on athletic performance are still widely misunderstood.

Recently, my friend and I decided to put on our science hats and do a thorough review of the literature regarding how Vitamin D affects athletic performance.

Since my formal training and current day job is a scientist, we decided to make this thing science-worthy, and thus the paper ended up being a monster at 8,000+ words, and was published in a peer-review journal (You can find the full article here).

For now, however, I have broken it down to a few key points.

Vitamin D: What is it?

Vitamin D is a fat-soluble vitamin, meaning they need fat to be absorbed and transported around the body (they can also be transported by certain proteins, and in the case of Vitamin D it is transported by Vitamin D-binding proteins).

Vitamin D is quite interesting in that it is a vitamin, a precursor to steroid hormones, is involved in regulating exercise-induced inflammation, tumor suppressor genes, neurological function, cardiovascular health, glucose metabolism, bone health and skeletal muscle performance.

Basically, it affects an obscene amount of processes in the body.

Another interesting aspect of Vitamin D is that your body can manufacture it through an intricate process using sunlight to turn a form of cholesterol into Vitamin D (so don’t be afraid to eat your eggs!).

Vitamin D Deficiency in Athletes

Currently, it is estimated that 88.1 % of the world’s population has inadequate Vitamin D levels [1]. A recent meta-analysis pooling 23 studies with 2313 athletes found that 56 % of athletes had inadequate Vitamin D levels [3]. Which, when you look at it on the surface, appears that athletes may be less susceptible than others regarding Vitamin D deficiency.

This may be true for a couple reasons: 1) in general, athletes tend to consume higher nutrient dense diets, and 2) athletes are more likely to be outdoors for their sports (e.g. track, soccer, football, baseball, cycling, etc.).

However, 56% is still a majority of the population. Thus, it would stand to reason that correcting a deficiency in Vitamin D may improve performance amongst athletes.

Can Vitamin D Improve VO2 Max?

 There have been numerous studies (7 which we found), that were either correlational or interventional in terms of Vitamin D and VO2 Max (a marker of aerobic fitness). The correlation studies are a mixed bag, with some showing positive correlation and some showing no correlation.

These results are not surprising as the populations, the assays to measure Vitamin D, and the analytic methods were substantially different across studies.

However, the fact that there were no negative correlations should give us some insight that Vitamin D levels might have some ability to improve VO2.

In the intervention study, Vitamin D (6000 IU) led to a slight improvement in VO2. Now, it’s important to note that this was a short-term study and the improvement was only 1.8% greater than the placebo.

More studies must be done to determine if it really can improve VO2, and to what extent.

Recovery and Power Production

My partner and I also dove into the research of how Vitamin D effects recovery and power production. This was a nightmare as most of the research was in animals or cells and they used crazy doses, as much as 332,000 IU/kg which would be like giving me 28,000,000 IU in an injection (no thank you).

While the research did show it was beneficial for recovery from injury, the way the study was done makes it impossible to translate to humans.

There was one study that showed that 4,000 IU per day improved markers of muscle damage. So it might improve recovery but again, it is a little all over the board, and more research really needs to be done before I can make any recommendations.

In regard to power production, there is also conflicting evidence showing that Vitamin D supplementation improves power;  some studies show it does and some show no effect. The one study that did show improvements demonstrated that that 4000 IU per day prevented training induced decreases in power production by about 26% when compared to placebo.

I think this is likely a function of the current Vitamin D levels and training status of the individuals.

My thoughts are that correcting a vitamin D deficiency would most likely help with recovery so you can produce more power the following days, but significant doses on top of correcting a deficiency probably will not improve power.

Vitamin D and Testosterone

Let’s be real for a minute; you probably need/want more testosterone.

One of the most consistent things we found in doing this research was that Vitamin D was correlated to testosterone, and that giving men in their 50’s roughly 3,300 IU per day improved their circulating levels of Vitamin D and Testosterone (total, bioactive, and free).

Thus, it seems like Vitamin D can help with testosterone levels. Now, this isn’t to say taking vitamin D will automatically improve your testosterone, but some research suggests it might be helpful. 

The Wrap Up.

Let’s not make this more complicated than it needs to be. Vitamin D plays a role in regulating a lot of important things in your body, and being deficient in it might hamper your performance, recovery, and testosterone levels.

Since 88% of the world’s population is Vitamin D deficient, I would highly recommend you get tested. Should you find out that you are, in fact, lacking in this area, then I suggest you find an appropriate dosing to correct any deficiency. Or, just get some more sun. If you aren’t deficient, you probably don’t need to be taking any supplemental Vitamin D, as the science does not indicate that it would improve anything, including your performance.