Low vitamin D levels are a common problem. Studies show that up to 75% of the population is deficient in vitamin D, dubbed the “sunshine vitamin,” because the best source is exposure to the sun. Vitamin D is important for bone health, a healthy immune system and for cell growth and division. In fact, vitamin D influences over 1,000 different genes including genes that regulate inflammation in the body. That’s why vitamin D may reduce the risk of some autoimmune diseases such as multiple sclerosis and rheumatoid arthritis. Some studies even suggest it improves exercise performance. Is there any truth to this?
Vitamin D and Exercise Performance
According to research published in the journal Medical Science Sports Exercise, vitamin D affects exercise performance, especially in older people. Muscle cells have receptors for vitamin D on their surface, and vitamin D can directly impact muscle function. Vitamin D also regulates calcium levels, which is important for healthy muscle function. As a result, people who are vitamin D deficient may feel fatigued and have muscle weakness.
How does it affect exercise performance? Vitamin D deficiency reduces the ability to do high-intensity and strength exercises the most. These types of exercise activate fast-twitch muscle fibers, the type that generates force and power, and vitamin D deficiency decreases their size and number.
Does this mean supplementing with vitamin D can improve your exercise performance or make you stronger when you lift weights at the gym? Only if you’re deficient. A study published in Osteoporosis International showed that vitamin D supplements boost muscle strength in adults who have low levels of vitamin D but not those who have normal levels. Still, with the high rate of vitamin D deficiency, a significant number of people may have reduced strength and sub-optimal exercise performance because of low levels of vitamin D. It may increase their risk of injury too.
Vitamin D and Muscle Injury
Recently a study looked at injury rates among 89 NFL football players and compared them to their vitamin D levels. They found that players who missed time on the field due to muscle injuries had lower levels of vitamin D. The average vitamin D level of these players was 19.9. Vitamin D deficiency occurs when vitamin D levels drop below 20 ng/ml. Levels between 20 and 31.9 ng/ml are considered to be insufficient.
This study doesn’t show cause and effect since there could be some a factor other than vitamin D that accounts for the higher injury rate but combined with other evidence, it suggests that vitamin D is important for muscle health.
Should You Supplement with Vitamin D if You’re Active?
Vitamin D supplements aren’t likely to improve your strength or exercise performance unless you have low vitamin D levels. Your vitamin D level should be 32 ng/ml or higher and a minimum vitamin D level of 40 ng/ml is best. Before taking vitamin D supplements, get a blood level checked to find out if you’re deficient. You can get adequate vitamin D by exposing your skin to sunlight for 15 minutes three days a week, but if your levels are low, a supplement will boost your levels more quickly. Even then, it can take 6 weeks or more to raise low vitamin D levels into the normal range.
The Bottom Line?
Can vitamin D boost exercise performance, strength and reduce injury? There’s preliminary evidence that it can if your levels are low. Ask your doctor to check your vitamin D level, and find out if you’re one of the many who is deficient in this vitamin.
Med. Sci. Sports Exerc. 2009 May; 41(5): 1102-1110.
Osteoporosis International. Volume 22, Number 3, 859-871.
Medscape.com. “Alarming Vitamin D Deficiencies in NFL Football Players”