Vitamin D Deficiency & Proximal Muscle Weakness

Vitamin D is increasingly found to play an important role in numerous body functions. Your body manufactures vitamin D naturally when your bare skin is exposed to the sun. Yet sedentary Americans who spend most of their time indoors, or who slather themselves with potent sunscreens when they do go outdoors, are at risk for vitamin D deficiency. One potentially debilitating symptom of vitamin D deficiency is proximal muscle weakness.

Proximal Muscle Weakness

Proximal muscles are those closest to the body and that attach the limbs to the trunk, as opposed to distal muscles, which are located in the extremities. The muscles of the shoulder girdle and the muscles of the hip are proximal muscles. Weakness in proximal muscles can interfere with everyday activities like combing your hair or walking. A 2005 study published in the "British Medical Journal" linked Vitamin D deficiency to proximal muscle weakness in the elderly, calling it a public health problem that leads to falls and fractures.

Vitamin D Deficiency

The Linus Pauling Institute describes vitamin D as a fat-soluble vitamin that is essential for the efficient use of calcium by the body. The prevalence of vitamin D deficiency is on the rise in the United States. The National Health and Nutrition Examination Survey 2005 to 2006 data showed vitamin D deficiency to afflict 41.6 percent of Americans, with darker-skinned individuals being even more at risk. Among African Americans, 82.1 percent were found to be vitamin D-deficient, and 69.2 percent of Hispanics were also found to be deficient.

Vitamin D and Muscle Function

A 2009 article written by Qatar Orthopaedic and Sports Medicine Hospital researcher B. Hamilton and published in the "Scandinavian Journal of Medicine and Science in Sports" points out that, while much research on vitamin D deficiency and muscle function has been geared toward the elderly, vitamin D deficiency may play an important role in athletic underperformance and risk of injury. While the specific mechanisms by which vitamin D impacts muscle are unclear, Hamilton chronicles accumulating evidence that there is a link between vitamin D, skeletal muscle and athletic performance.

Sources of Vitamin D

According to the Mayo Clinic, dietary sources of vitamin D include eggs, fish, fortified milk and cod liver oil. Exposing your bare skin to natural, unfiltered sunlight for as little as 10 minutes daily may be sufficient to prevent vitamin D deficiency. If you are unable to get enough sunlight, vitamin supplements may also be an option. The Clinic notes that humans need vitamin D in the form of D2 and D3.