It doesn't seem like a week goes by without a new discovery relating to Vitamin D. I learned something new about Vitamin D this week. Most people are familiar with the role of Vitamin D in bone health. It is known to regulate the amount of calcium in the body. However, what I didn't know was the importance of Vitamin D for the functioning of skeletal muscle. Athletes with low Vitamin D have been found to have lower performance. Muscle weakness and early fatigue appear to be a consequence of low vitamin D. The good news is that when the Vitamin D deficiency is corrected, muscle performance returns to normal.
Reference: Pediatr Clin N Am 57 (2010) 849–861.
So who is at risk for Vitamin D deficiency? The greatest risk appears to be people who have limited exposure to the sun (i.e. Northern latitudes, winter months). Surprisingly, darker skinned individuals are also at risk for Vitamin D deficiency as they are not able to produce as much Vitamin D in response to sun exposure. I also learned that obese individuals are at risk because they only produce 1/2 as much Vitamin D in response to any given amount of sun exposure. This, in turn, can result in reduced muscle performance in obese individuals. This can lead to reduced activity and even greater obesity. A vicious cycle indeed. The good news for obese individuals is that absorption of Vitamin D from food sources (and vitamins) is not affected.