Everyone should be concerned about having an adequate level of vitamin D, the sunshine vitamin. But if you’re athletic, work out or participate in sports, vitamin D assumes importance for a different reason. Some research shows low vitamin D levels may impact sports performance. It’s possible to have a vitamin D deficiency and not know it since a deficiency of this vitamin that’s so vital for good health can be subtle. If you’re finding it hard to get through your workouts or feeling weak and tired, don’t chalk it up to overtraining. It could be a low vitamin D level. What impact does vitamin D have on sports performance?
 
Vitamin D Deficiency: It’s Surprisingly Common
You can usually meet your requirement for most vitamins by eating a varied and balanced diet, but vitamin D is an exception. The best source of vitamin D isn’t food, although fatty fish and fortified foods like milk and cereal contain respectable amounts. Most people get vitamin D from the exposure to the sun. When sunlight hits your skin, it converts vitamin D precursors to forms that can be modified by your liver and kidneys to make active vitamin D.
 
Unfortunately, not everyone gets adequate exposure to sunlight, especially during the winter months when there’s less direct sunlight and people spend more time indoors. This has created a mini-epidemic of vitamin D deficiency. Some research shows up to 75% of people have low or borderline-low levels of vitamin D.
 
How Does Vitamin D Impact Athletic Performance?
An interesting study published in the journal Cerebrovascular Diseases showed that older women deficient in vitamin D reduced their risk of falling when they supplemented with 1,000 I.U. of vitamin D a day. What’s more interesting is how supplementing with vitamin D seemed to benefit these women. They found that the women who supplemented with vitamin D had a higher percentage of fast-twitch muscle fibers and these fibers were greater in size.
 
This is an interesting finding since fast-twitch muscle fibers are important for speed and power. It’s fast-twitch muscle fibers that are activated when you sprint, do plyometric moves, swing a kettlebell or lift a heavy weight. Having a greater density of fast-twitch muscle fibers and fibers that are larger works in your favor when you’re doing high-intensity or power moves. If this holds true, it’s not a stretch to say that low levels of vitamin D can impact athletic performance.
 
Another study published in Medicine and Science in Sports and Exercise scoured the world’s literature looking for a link between athletic performance and vitamin D. They found that athletic performance peaks when vitamin D levels are 50 ng/ml or greater. Vitamin D levels of 30 ng/ml. are considered adequate for bone health. This is further supported by observations that peak athletic performance usually coincides with the late summer months, when athletes have had several months of peak sunlight, and tends to decline during the late autumn and winter. Of course, other factors like the “winter blues” and the cold could also account for this, but low vitamin D levels could also play a role.
 
A Low Vitamin D Level May Increase Your Risk for Injury and Stress Fractures
Have you ever experienced a stress fracture? Check your vitamin D level. Vitamin D helps your intestines absorb and use calcium to build fracture-resistant bones. One study showed that athletic adolescent girls who got more vitamin D were less likely to develop stress fractures. Even if you’re getting enough calcium in your diet, you need vitamin D to help with absorption. Another study found a link between higher vitamin D levels and greater arm strength. One of the symptoms of vitamin D deficiency is muscle weakness and fatigue.
 
Are You at Risk for Vitamin D Deficiency?
You may spend time outdoors, but if you’re slathering on sunscreen before heading outside, you may not be absorbing enough vitamin D. If you have more pigment in your skin, you also need more sunlight exposure to maintain adequate vitamin D levels.  Older people are also more likely to be vitamin D deficient. That’s why it’s important to know your vitamin D level and take a supplement if your level is even marginally low. Don’t forget that preliminary research shows vitamin D is important for a healthy immune system and may protect against some autoimmune diseases, some types of cancer, other chronic disease like type 2 diabetes and even impact your mood. It’s important for overall health – both mental and physical.
 
The most accurate test for vitamin D deficiency is to check a 25-hydroxy vitamin D level. It’s a simple blood test your doctor can order for you. Make sure you know your number.
 
References:
Journal International Journal of Sport Nutrition and Exercise Metabolism 2008 Vol. 18 No. 2 pp. 204-224.
Medicine and Science in Sports and Exercise. May 2009. Vol. 41. No. 5.
Arch Pediatr Adolesc Med. 2012 Mar 5.

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