The Importance of Vitamin D for Athletes

By Patrick Dixon, Head of Applied Sports Science at Amp Human 


As it applies to athletic performance, a higher concentration of vitamin D (greater than 30ng/mL) is shown to improve muscle strength and power, muscle recovery, sleep quality, preventing stress fractures and support the immune system in its defense from respiratory illness. If you’re looking to improve your athletic performance, recovery and give yourself a fighting chance against seasonal illness, supplementing with vitamin D should be an essential part of your daily routine.

Vitamin D for the Athlete

Athletes & practitioners have long-known the value of vitamin D in relation to bone health, however newer research suggests that vitamin D plays a far more significant role in performance. Below we explore five key benefits for supplementation in athletes at all levels. 

1. Improved muscle strength and power 

Sport is often defined by the ability to move through space, be it on the bike, trail, field or in the pool. A core component of how effectively we perform at our chosen sport is determined by our strength and power. Gains in muscle strength and the rate at which that strength is produced i.e. power, is the reason why athletes at all levels incorporate strength based training as part of their program. 

Vitamin D supplementation may increase muscle performance in two ways: (i) improving cell growth and development, specifically of fast-twitch muscle fibers responsible for strength and power output (ii) improving signal sensitivity from the brain to the muscle leading to faster and better muscular contraction and therefore, more explosive movement. Conversely, deficiency in vitamin D may result in a breakdown of fast-twitch muscle fibers and reduce the muscle’s ability to contract and relax effectively, which can limit muscular performance and efficiency for athletes. 

What the research says: 

- Increases in strength and power have been studied in athletes with positive results after an 8-week treatment of 5000 IU/day of vitamin D3. The vitamin D3 group had a significant improvement in both their 10-m sprint times and vertical jump when compared to the placebo group. (full study HERE)

- In another study where trials lasted from 4 weeks to 6 months, vitamin D supplementation significantly increased muscle strength in both the upper and lower body. (full study HERE).

2. Improved muscle recovery

Repeated muscle contractions during exercise leads to microtears in the muscle that need time to scar down and heal. Additionally, the body will experience inflammation post-exercise which can lead to muscle soreness, commonly referred to as delayed onset muscle soreness (DOMS). Both of these outcomes will limit athletic performance in the training days that follow. 

Vitamin D plays a critical role in reducing inflammation due to its ability to inhibit the production of proinflammatory markers. Some of those markers are thought to be directly related to the resulting muscle damage from exercise. Vitamin D supplementation may help athletes recover more quickly during the workout and be better prepared for their next session.

What the research says: 

- Higher pre-exercise vitamin D levels are associated with faster recovery of skeletal muscle strength after an acute bout of intense exercise. (full study HERE)

- In a study looking at peak force after intense exercise, the group supplementing vitamin D only decreased by 6%, while the placebo group’s power decreased by 32%. The supplemental group also showed a blunted increase in muscle damage biomarkers after the exercise protocol. (full study HERE)

- The vitamin D supplementation group showed a 14% improvement at 48hrs and 13.7% improvement at 7 days in torque recovery. 88% of the variation in peak torque recovery could be explained by the change in serum vitamin d levels. (full study HERE)

3. Prevents stress fractures

Stress fractures account for almost 20% of all sports injuries. Athletic performance depends on strong bones to act as the foundation for movement when undergoing the speed, force and torque required by sport. Beyond the financial cost of treatment and physical pain experienced with such injuries, there is also the lost training time and missed opportunity for competition which can make or break an athlete’s season.

Vitamin D’s most well-known function is to support bone growth, remodeling and density by influencing calcium absorption. For athletes, weaker bones are more susceptible to stress fractures and even full fracture. Optimal vitamin D levels are critical to the proper absorption of calcium so the body can fortify bones and ultimately improve their strength and resilience. 

What the research says: 

- Research has shown that vitamin D levels above 30ng/mL can improve calcium absorption by up to 65%. (full study HERE)

- In college athletes, the rate of recurrent stress fracture was 21.5% and accounted for 20.7% of season-ending injuries (full study HERE). Vitamin D3 supplementation was shown to significantly decrease stress fracture rate in college athletes. (full study HERE)

- In tactical athletes, those with vitamin D levels below 30ng/mL were 3.6 times more likely to develop stress fractures during training than those with sufficient levels. (full study HERE)

4. Improved sleep quality

Quality rest is a top priority for athletes. At a high level, a lack of quality sleep impairs cognition, learning and mental well-being. Physically, it disrupts growth and repair of cells, glucose metabolism and lowers resistance to respiratory infection. Hormonally, deep sleep is where the pituitary gland releases growth hormone, which plays an important role to maintain, build, and repair healthy tissue in the brain and other organs. Growth hormone also plays a critical role in injury recovery and in repairing muscle tissue after exercise. 

Vitamin D receptors have been found in the areas of the brain that control sleep duration and quality. Studies have shown strong links between vitamin D supplementation and improved sleep quality, reduced sleep latency and increased sleep duration. Getting to deeper sleep states is where the brain can truly relax and recover by flushing out metabolic waste and allowing fresh nutrients to replace them so you’re ready to perform the next day. 

What the research says: 

- Studies reporting global sleep quality show that 50–78% of elite athletes experience sleep disturbance and 22–26% suffer highly disturbed sleep. (full study HERE)

- Those with vitamin D deficiency have shown an increase in sleep disorder risk by up to 60%. (full study HERE)

- Vitamin D supplementation has been shown to improve sleep quality, reduce sleep latency, raise sleep duration and improve subjective sleep quality. (full study HERE)

5. Improved immune health

There is some truth to the idea that repeated intense exercise may lead to a “window” of immune system depression, but not in the way you may think. The exercise itself isn’t the cause, but rather inadequate recovery in the form of nutrition and sleep can lower the body’s immune system defense. Traveling for competition and exposure to larger groups at events has also been linked to greater rates of illness. 

Vitamin D plays a key role in supporting immune function, specifically in the lungs where it helps the cell lining defend against pathogens like the flu. It does this by activating immune cells that can both fight the infection as well as moderate the inflammatory response that comes with it. The benefit of higher vitamin D levels is a more efficient response to infection as well as a potential to reduce the severity of symptoms.  

What the research says: 

- Elite athletes were 4.5x more likely to develop an upper respiratory infection than their recreationally trained counterparts during heavy training and competition. (full study HERE)

- A recent meta-analysis found that up to 56% of athletes may have insufficient levels of vitamin D. (full study HERE)

- Observational studies predominantly report significant associations between low vitamin D status and increased risk of both upper and lower respiratory tract infections. (full study HERE

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