Vitamin D helps build strong bones. Every milk carton says so. But the big D can have another effect: It can keep your immune system from attacking your own joints. With that ability, along with its bone-strengthening skills, vitamin D may reduce the risk of crippling rheumatoid arthritis.
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The disease does its damage when overactive immune cells attack joints, causing inflammation, pain, and immobility. In this month's issue of Arthritis & Rheumatism, researchers focused on older women's risk of getting arthritis over an 11-year period and tried to relate it to the amount of vitamin D in their diets, as well as other bone-promoting substances like calcium. From the Iowa Women's Health Study, the scientists got detailed information about the eating habits of nearly 30,000 women ages 55 to 69. Women who took in the most vitamin D turned out also to be the ones with the lowest rates of the disease. Getting D from supplements, rather than food, had the biggest effect. (Few foods are naturally rich in Vitamin D, though milk and eggs do have some.) This held true when the researchers looked at the detailed medical records of 152 of these women who were diagnosed with rheumatoid arthritis.
This implies a new, more prominent role for vitamin D. The big job of the vitamin, researchers used to think, was to regulate levels of calcium in the body. But this and other research indicates vitamin D, independent of calcium, can affect the immune system and joints like knees and elbows. The vitamin works its way into the fluid of these joints, where it appears to hinder the activity of immune cells called T cells, which produce inflammation. These effects have also been noted in multiple sclerosis, another disease in which the body's immune system turns and assaults its host. In these cases of attack, D may stand for defense.
