The researchers say a failure amongst the elderly to get enough vitamin D either from their diets or exposure to the sun, heightens their risk for muscle weakness and poor physical performance.

This they say is a worry as vitamin D plays an important role not only in bone health but research also suggests it may help protect against diabetes, cancer, colds, and tuberculosis, especially in view of the number of seniors who are deficient in vitamin D.

The research team found that in a sample of 976 adults who were 65 or older when tested, 75 percent of women and 51 percent of men had insufficient vitamin D levels.

The researchers tested the participants' physical performance by timing their walking speed, as well as their ability to get up from a sitting position and keep their balance while standing in increasingly more challenging positions.

They also measured handgrip strength, a predictor of future disability.

Lead author Dr. Denise K. Houston found that physical performance and grip strength were 5 to 10 percent lower in people with low blood levels of vitamin D levels, compared with those with normal levels.

Even after factors which might influence the results were taken into account, such as a person's weight, level of physical activity, the season of the year, mental abilities, overall health condition and anemia, the finding remained.

Vitamin D is derived from the sun's ultraviolet rays and from certain foods such as fortified milk, juice and cereals but it can be difficult to absorb sufficient amounts of the vitamin through diet alone.

Older adults are inclined towards lower vitamin D levels because of reduced exposure to the sun and because their skin is less able to produce vitamin D from sun exposure compared with younger adults.

The researchers estimate that 1 in 4 people over age 60 have low vitamin D levels which equates to 12 million people.

Current guidelines recommend that people between the ages of 50 and 69 get 400 international units (IUs) of vitamin D per day and for those over age 70 to get 600 IUs but are based primarily on vitamin D's effects on bone health.

Dr. Houston believes 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 as people become elderly.

Dr. Houston recommends supplements of vitamin D3 because it will convert into an active form that the body can absorb and use.

The study is published in the April issue of the Journal of Gerontology: Medical Sciences.