Vitamin D is a fat-soluble vitamin that the skin synthesizes upon exposure to sunlight. However, it is not uncommon to be deficient in vitamin D, especially during the winter and in people who do not sufficiently expose themselves to the sun. Vitamin D is also found in low amounts in egg yolks and oily fish. Vitamin D is essential not only for healthy bones, but also for proper brain function, a healthy immune system, cell differentiation and muscle function, as described in the "Manual of Dietetic Practice."
Muscle Weakness
The December 2010 issue of "Nutrition Journal" reports that muscle weakness is a characteristic symptom of vitamin D deficiency. These patients often report nonspecific muscle weakness, aches and pains. Weak muscles are a risk factor for falls. Because vitamin D deficiency is also associated with weak bones, vitamin D-deficient patients are more likely to fall and fracture bones. This is especially pertinent to the elderly, who might also have impaired coordination.
Fat Content of Muscle
The April 2010 issue of the "Journal of Clinical Endocrinology and Metabolism" reports that the body's levels of vitamin D are also associated with the degree of fat infiltration in muscle, i.e. the amount of fat in muscles. Higher muscle fat content is associated with lower levels of muscle strength and physical performance. The 2010 report says a negative association was found between vitamin D levels and muscle fat content, with subjects who have higher levels of vitamin D having the least muscle fat content. The subjects in this study were healthy young women between 16 and 22 years old.
Athletic Performance
The May 2009 issue of "Medicine and Science in Sports and Exercise" reports that vitamin D exerts a potent effect in numerous body tissues, including nerve and muscle tissue. The study reports that it was been known as early as the 1950s that vitamin D can improve athletic performance. The authors also report that it has now been found that vitamin D increases the size and number of type 2 muscle fibers -- the fibers responsible for anaerobic strength production. The authors conclude that peak athletic performance is achieved when vitamin D levels "approach those obtained by natural, full-body, summer sun exposure."
Heart Muscle
Vitamin D is important not only in skeletal muscle function, but also in heart muscle. According to the August 2010 issue of "Molecular Nutrition and Food Research," vitamin D-deficient children who suffer from severe cardiac failure can be successfully treated with vitamin D and calcium supplementation. The authors also note that most adult heart failure patients tend to be vitamin D-deficient, and conclude that vitamin D supplementation can be beneficial to patients with or at risk for heart disease.
References
- "Manual of Dietetic Practice (fourth edition)"; T. Briony and J. Bishop; 2007
- "Nutrition Journal"; "Vitamin D in Health and Disease: Current Perspectives"; R. Zhang et al; December 2010
- "Journal of Clinical Endocrinology and Metabolism"; "Vitamin D Status and Its Relation to Muscle Mass and Muscle Fat in Young Women; V. Gilsanz et al; April 2010
- "Medicine and Science in Sports and Exercise"; "Athletic Performance and Vitamin D"; J.J. Cannell et al; May 2009
- "Molecular Nutrition and Food Research"; "Vitamin D Deficiency and Myocardial Diseases"; S. Pilz et al; August 2010
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