Below is a great review on Vit D and muscle tissue/function. I need to thank Dr. John Berardi at Precision Nutrition for finding this one. I love the PN (Precision Nutrition) system and use it with all my athletes.
Keep in mind that while a Vit D deficiency has many issues (poor muscle function being one of them), BUT this does NOT mean that mega doses of it will promote more muscle growth (atleast not that I have seen in the literature anywhere).
Keep in mind that sunlight is going to be your best source of Vit D as the body has this super cool autoregulatory system set up where it is impossible to get too much Vit D from the sun!
Although you can still get a nasty sun burn and look like Randy The Red Lobster, so be careful. My favorite way to get more sunlight is kiteboarding in warm climates!
At the Annual ACSM conference I went to this past Spring, a top researcher from Australia stated (paraphrasing) that Vit D and Iron are the only 2 tests that she conducts on female athlete's training for the Olympics since the change of being defficient is so high.
Vitamin D and skeletal muscle tissue and function.
Ceglia L.
Mol Aspects Med. 2008 Dec;29(6):407-14. Epub 2008 Aug 8
Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Bone Metabolism Laboratory, 711 Washington Street, Boston, MA 02111, United States.
This review aims to summarize current knowledge on the role of vitamin D in skeletal muscle tissue and function. Vitamin D deficiency can cause a myopathy of varying severity. Clinical studies have indicated that vitamin D status is positively associated with muscle strength and physical performance and inversely associated with risk of falling. Vitamin D supplementation has shown to improve tests of muscle function, reduce falls, and possibly impact on muscle fiber composition and morphology in vitamin D deficient older adults.
Molecular mechanisms of vitamin D action on muscle tissue include genomic and non-genomic effects via a receptor present in muscle cells. Genomic effects are initiated by binding of 1,25-dihydroxyvitamin D [1,25(OH)(2)D] to its nuclear receptor, which results in changes in gene transcription of mRNA and subsequent protein synthesis. Non-genomic effects of vitamin D are rapid and mediated through a cell surface receptor. Knockout mouse models of the vitamin D receptor provide insight into understanding the direct effects of vitamin D on muscle tissue.
Recently, VDR polymorphisms have been described to affect muscle function. Parathyroid hormone which is strongly linked with vitamin D status also may play a role in muscle function; however, distinguishing its role from that of vitamin D has yet to be fully clarified.
Despite the enormous advances in recent decades, further research is needed to fully characterize the exact underlying mechanisms of vitamin D action on muscle tissue and to understand how these cellular changes translate into clinical improvements in physical performance.
