The Role of Vitamin D in Preserving Muscle Strength in Seniors

Source: Tufts University
July 16, 2002 (Reviewed: July 16, 2004)

The reduced muscle mass and diminished strength that commonly occur in the elderly can have potentially serious consequences, including limited ability to perform activities of daily living, or, worse, falls and debilitating fractures. Helping patients preserve muscle strength may greatly improve their quality of life.

Because muscle weakness is associated with vitamin D deficiency, researchers from the Netherlands reviewed the literature on the relationship between vitamin D deficiency, muscle function, and falls in seniors to explore whether vitamin D supplementation can improve muscle strength and functional ability. Their review is published in the American Journal of Clinical Nutrition.

Vitamin D basics

The metabolism of vitamin D begins with the conversion of 7-dehydrocholesterol, a naturally occurring substance in the skin, to previtamin D3. This occurs only in the presence of ultraviolet rays from sunlight. Previtamin D3 is then carried, bound to a protein, to the liver where it is hydroxylated to 25(OH)D3 and then to the kidneys where it is further metabolized to the biologically active form of vitamin D, 1,25(OH)D3.

In addition to sunlight exposure, vitamin D can also be obtained from dietary sources, including fatty fish (such as sardines and salmon), and vitamin D-fortified foods. (In the US, milk is routinely fortified, as is some margarine and cereal.) Decreased dietary intake, inadequate exposure to sunlight, and renal or hepatic insufficiency can all play a role in vitamin D deficiency.

Supplementation may improve muscle function

Studies have found that seniors with low levels of vitamin D have reduced leg extension power, handgrip strength, ability to climb stairs, and ability to walk distances. Some research shows that supplementation to correct a deficiency leads to improvements in knee extension strength, walking distance, and functional abilities.

Can vitamin D supplementation prevent falls?

On average, one-third of all seniors experience at least one fall per year. Vitamin D deficiency apparently affects the muscles of the lower limbs that are essential for balance and walking. The authors say that there is a correlation between serum vitamin D concentrations and falls, but whether supplementation can reverse the trend remains unclear.

In one study of 148 women with low levels of serum vitamin D, those receiving 8 weeks of supplementation with calcium and vitamin D had a lower risk of falls compared with those receiving only calcium supplementation (RR 0.24 vs. 0.45, P<0.05). However, another study of healthy adults aged 65 and older who received calcium and vitamin D for 3 years found no significant reduction in falls in treatment subjects compared with those receiving placebo.

Preserving muscle strength

While the potential role of vitamin D supplementation in preventing falls in seniors remains to be elucidated, supplementation may help preserve muscle strength and functional ability. Because of its critical role in the absorption of calcium, it is of particular importance for seniors with limited exposure to sunlight and inadequate dietary intake. Since vitamin D is toxic in high doses, patients should be advised to take only the recommended dose.

Source

• Vitamin D deficiency, muscle function, and falls in elderly people. H. Janssen, M. Samson, H. Verhaar,  et al., Am J Clin Nutr , 2002, vol. 75, pp. 611--615

Related Links
Vitamin A Tied to Fracture Risk in Older Women
Falls Can be Prevented
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