NEW YORK (Reuters) -- Older people whose knees are affected by osteoarthritis -- the most common disease of the joints in the elderly -- run the risk of it worsening if they don't get enough vitamin D, researchers say.
Their report in the September issue of the Annals of Internal Medicine is the first to link low dietary intake and low blood levels of the sunshine vitamin with progression of this disease, which strikes more than 10% of all people over the age of 65.
The researchers, led by rheumatologist Dr. Timothy McAlindon of the Arthritis Center at Boston University, found a threefold greater risk of osteoarthritis progression in men and women with low dietary intake and low blood levels of vitamin D.
"On the other hand, we found no evidence that low intake and low serum levels of vitamin D influence the risk of developing osteoarthritis in a previously normal knee," McAlindon says.
The Boston team studied 556 elderly people whose knees had been x-rayed for osteoarthritis between 1982 and 1985, then again between 1992 and 1993. Study participants answered questionnaires about their daily nutritional intake, and their blood was sampled for vitamin D levels.
In people diagnosed with the disease and who had low levels of vitamin D in their blood and in their diets, subsequent knee exams showed a continuing narrowing of the joint space, indicating a breakdown in the knee's cushioning cartilage. Some joint x-rays also showed development of bony spurs called osteophytes, which are another hallmark of disease progression.
These findings, the authors say, emphasize the fact that osteoarthritis is more than just a disease of the joint cartilage, as it has been traditionally viewed, but also of the bone itself.
"Our results, which need confirmation, suggest that persons with osteoarthritis of the knee... may benefit from increased vitamin D intake or exposure to sunlight," the authors conclude.
They add that studies are also needed to determine if a similar link exists with other forms of osteoarthritis, including that of the hand and the hip.
Vitamin D is important for the maintenance of healthy bone. The richest dietary source of Vitamin D is fortified milk. Other good sources include sardines, herring, salmon, tuna, liver, dairy products, and egg yolk. Vitamin D is also formed by the action of ultraviolet rays in sunlight on chemicals in the skin.
Current federal guidelines recommend about 400 international units per day.
Source: Annals of Internal Medicine (1996;125:353-359)
