Vitamin D May Protect Against Rheumatoid Arthritis


Women with highest levels of vitamin D intake are about one third less likely to develop rheumatoid arthritis (RA) than women with the lowest levels, findings from a new study suggest.

Although vitamin D is best known for its role in building bones, it may also have effects on the immune system, senior author Dr. Kenneth G. Saag, from the University of Alabama at Birmingham, and colleagues report in the medical journal Arthritis and Rheumatism.

To determine the effect of vitamin D intake on rheumatoid arthritis risk, Saag's team analyzed data from nearly 30,000 women, between 55 and 69 years of age, who participated in the Iowa Women's Health Study. All of the women were rheumatoid arthritis-free at study entry in 1986, and vitamin D intake was ascertained through food frequency questionnaires.

During the 11-year follow-up period, 152 confirmed cases of rheumatoid arthritis were identified, the investigators report.

Both dietary and supplemental vitamin D intake were inversely linked with rheumatoid arthritis risk, the authors found. High dietary (at least 290 IU/day) and supplemental (at least 400 IU/day) intake were associated with 28 percent and 34 percent reductions, respectively, in the risk of rheumatoid arthritis.

However, only the association between vitamin D supplement intake and rheumatoid arthritis risk was statistically significant.

No single food item high in vitamin D or calcium was strongly linked to rheumatoid arthritis risk, the researchers point out. However, there was a trend toward a lower rheumatoid arthritis risk with greater intake of milk products.

Although the effects of vitamin D on the immune system are not yet fully defined, "the results from this study suggest a possible role for vitamin D in reducing the risk of an immunologic disorder," the authors state. Further studies are needed to verify these findings, they add.

SOURCE: Arthritis and Rheumatism, January 2004.