Vitamin D, which can be obtained from food and is produced naturally by the body through exposure to the sun, plays an important role in bone health and muscle function and may help protect against diabetes, cancer, colds and tuberculosis.

About 25 percent of people over age 60 have low levels of vitamin D, say researchers reporting in the April issue of the Journal of Gerontology: Medical Sciences.

Older adults are prone to low vitamin D levels, because they tend to get less exposure to sunlight, and their skin is less efficient in producing vitamin D from sun exposure, said the study's lead author, Denise Houston, an instructor in internal medicine-gerontology at Wake Forest University School of Medicine. Older adults also may not get enough vitamin D from dietary sources such as fortified milk, juice and cereals.

She and her colleagues analyzed data from a study of 976 Italians age 65 and older and found that those with low levels of vitamin D scored five percent to 10 percent lower in tests of physical performance and grip strength.

While the researchers didn't look at whether low vitamin D levels actually cause poor physical performance, they said the findings suggest the need for additional research in this area.

Current recommendations say that people ages 50 to 69 should get 400 international units (IUs) of vitamin D per day, and people over age 70 should get 600 IUs per day. However, many experts believe that may not be enough.

"Higher amounts of vitamin D may be needed for the preservation of muscle strength and physical function as well as other conditions such as cancer prevention. The current recommendations are based primarily on vitamin D's effects on bone health," Houston said.