Why should you care about vitamin D? Well, for one, you are likely deficient, or at least insufficient in this vitamin. I write this with confidence because multiple studies have shown the large prevalence of this condition. An estimated 1 billion people in the world are deficient or insufficient. One study found 42% of adolescents to be deficient. Another found 25% of young athletes deficient and another 48% insufficient (73% lacking overall). Another study found 52.3% of patients undergoing sports surgery such as ACL reconstruction to be insufficient, and one-third deficient. A study of NFL players found 30% deficient and 51% insufficient. You get the picture.
Risk factors for vitamin D deficiency include participation in primarily winter and spring sports, athletes participating in indoor sports, wearing sunscreen or skin-covering clothing, having dark skin and living at northern latitudes, variably defined as greater than 30° or greater than 40°. (The latitude of Chambersburg, PA and Philadelphia, PA is 39.9°, that of New York City is 40.7°.)
We have long known that vitamin D plays a critical role in regulating calcium levels and in bone metabolism. More recent knowledge has shone light on vitamin D as a performance enhancing substance. Below are four reasons athletes should pay attention to their vitamin D.
Strength
Vitamin D has direct effects on skeletal muscle cells. Increased levels of vitamin D have been associated with increased muscular strength. One study that measured grip strength, one repetition maximum bench press, one repetition maximum leg press, free weight squat and calf strength found that supplementation with vitamin D resulted in increased strength on these metrics.
Performance
Strength is great. What about performance in your sport? If you have low vitamin D you’re more likely to get cut from the team – literally. One study found that NFL players with lower vitamin D levels were more likely to be released from their team, whether for injury or performance reasons. One randomized controlled trial found that supplementation with 5000 IU of vitamin D daily was associated with increased vertical jump. Another randomized controlled trial noted increased jumping and movement efficiency in women after vitamin D supplementation. It has long been known that athletic performance has a seasonal variation, with peak performance occurring in late summer, and this correlates with seasonal variation in vitamin D levels.
Injury risk
In multiple studies, including military recruits and athletes, lower levels of vitamin D have been associated with increased risk of developing a stress fracture (though it does not seem to be correlated with osteoporotic fractures such as hip fracture). Lower vitamin D levels were found in NFL players who had at least one bone fracture as compared to players with no history of fracture.
Orthopaedic outcome
If you’re injured or undergoing surgery, it pays to optimize your vitamin D. We know that vitamin D positively influences both fracture and soft tissue healing. Patients undergoing total knee arthroplasty even score higher on functional testing if they have sufficient vitamin D.
Where can you get some of this great, legal performance enhancing substance? Sunlight is the main source. The skin synthesizes vitamin D in response to ultraviolet radiation. Dietary sources include eggs, oily fish, fortified foods and supplements. The recommended daily allowance of vitamin D for adults is 600 IU daily. Fair skinned individuals need 6 to 7 minutes of direct sunlight in the summer, and up to 30 minutes in the winter. Dark skinned individuals may need 3 to 6 times longer exposure. The amount of vitamin D one should consume (and where to draw the line for deficiency and insufficiency) is controversial, but many experts believe 600 IU is not enough. Toxicity is rare. It’s never been reported from sunlight or diet, and most reports from supplementation involve improperly manufactured supplements delivering much higher doses than advertised. For these reasons I’m comfortable being aggressive in dosing.
I first tested my level in 2009. At that time, with a level of 29 ng/mL, I was just below the lab reference range for normal (30-100 ng/mL), meaning I would be classified as ‘insufficient.’ Because I was just one nanogram below ‘normal,’ the doctor ordering the test told me my level was ‘fine.’ It wasn’t until years later that I even looked up the actual number. In 2017, I dug up that lab record, as I learned more about the importance of vitamin D. Many agree that an ideal range for athletes is 40-60 ng/mL, so I started myself on supplementation. Typically I am an advocate of getting all your nutrients from whole foods, but vitamin D is the one supplement I take. Fortification of food is fine – it has helped reduce vitamin deficiency on a population level, but I would submit that it’s essentially the same as supplementation, but in the form of processed food. We live at a northern latitude, try to avoid processed food, and we are big sunscreen users in my family. Supplementation it is.
With supplementation (3000 IU daily) my levels ticked up into the normal range and I noticed that I stopped getting sick. I used to get four to six bad colds per year. Now I rarely get sick. (Not being in residency or in New York City air quality may also have something to do with this.) I also stopped getting overuse injuries (though I have gotten smarter about training, too). It took four years to get myself into the optimal range for athletes. Not long ago, I asked my wife to pick up some more supplement when she was at the store and neglected to specify the dose. She grabbed a bottle of 5000 IU gels and so I decided to up my dose. After a whole summer of running and biking outdoors and supplementing with 5000 IU daily, my level was 54 ng/mL. I will continue to supplement more aggressively than the ‘recommended daily allowance’ of 600 IU. I’ll also keep wearing my sunscreen!
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