NEW YORK (Reuters Health) - Boston researchers report a link between low serum levels of vitamin D and decreased knee function in patients with osteoarthritis of the knee.

At the annual meeting of the American College of Rheumatology in San Antonio, Dr. David Felson of Boston University presented his team's findings from 221 subjects recruited from the Boston VA Medical Center. All had knee arthritis and reported knee pain on most days in the month before they joined the study.

The investigators measured blood levels of vitamin D at the start and again after 15 and 30 months. They compared change in vitamin D levels with changes in knee pain, physical function and muscle strength during the 30-month study period.

"We found a relationship between serum levels of vitamin D and knee function," lead investigator Dr. Kristin Baker told Reuters Health. Low levels were associated with higher levels of pain and disability and to a lesser extent muscle weakness.

"We also found that about 50 percent of the population were deficient in vitamin D," Baker commented.

In previous studies conducted in Minnesota, "almost 100 percent of the subjects with muscle pain were vitamin D deficient," she added. "It may be that vitamin D increases muscle strength or decreases postural sway, we don't really know."

Baker pointed out that this was not a study of vitamin D as a treatment for osteoarthritis, but she speculated that "we may need higher serum levels of vitamin D than we originally thought...This is one more piece of evidence that vitamin D intake should be increased."

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