Vitamin D increases the absorption of calcium and other minerals in the body, keeping the bones strong and cells happy. But, did you know that vitamin D also helps reduce body fat, increase muscle strength, and promote muscular development? One way vitamin D promotes such an array of fitness benefits is by binding to receptors on muscle cells that enhance muscle contraction and promote increased protein synthesis.
When the skin is exposed to UV radiation (or sunlight) the body can produce its own supply of vitamin D, by converting 7-dehydrocholesterol in the skin— Because of this, vitamin D is more accurately described as a hormone, than a true vitamin. Since the endogenous production of vitamin D depends greatly on sun exposure, and more people are protecting themselves from harmful UV radiation, then it should be of no surprise that vitamin D deficiency is common worldwide, especially in those athletes who train/perform indoors.
A recent systematic review, published in the Journal of Strength Conditioning Research, investigated the effects of vitamin D supplementation on muscle strength in athletes. The authors analyzed 5 randomized controlled trials, which were assessed as ‘excellent quality’, and 1 controlled trial, which was assessed as ‘good quality’. Overall, it was found that supplementing with vitamin D2 did not improve muscular strength; however, vitamin D3 supplementation promoted up to an 18.75% improvement in strength—pretty impressive!
How do you know if you are Vitamin D deficient?
The are many symptoms of vitamin D deficiency; but, to be accurate you should have your blood tested for 25-hydroxy-vitamin D or 25[OH]D, the blood metabolite of vitamin D. This test can be done by your physician or there are also several home “finger prick” tests available online. Current research suggests that athletes should strive to achieve blood 25[OH]D levels >75 nmol/L.
What form of vitamin D is best?
Research over the past decade clearly shows that vitamin D3 has much higher bioavailability than its sister, vitamin D2. In fact, research suggests that vitamin D3 is at least 300% more functionally effective than vitamin D2.
ACTION POINT: Vitamin D is fat soluble, so you can choose to take your daily amount in one shot or split it up among the day’s meals. We suggest taking a total (including what is in your multivitamin) of 2000 to 4000 IU of vitamin D3 daily. Research shows that doses in this range boost serum 25 [OH]D to > 75 nmol/L in about 8 weeks.
Chiang CM, Ismaeel A, Griffis RB, Weems S. Effects of Vitamin D Supplementation on Muscle Strength in Athletes: A Systematic Review. J Strength Cond Res. 2017 Feb;31(2):566-574.