A team of researchers set out to explore the association of vitamin D intake with the onset of rheumatoid arthritis (RA), an autoimmune disease marked by progressive joint destruction. Drawing on comprehensive data from the Iowa Women's Health Study, conducted over an 11-year period, the researchers assessed the vitamin D consumption of 29,368 women between the ages of 55 and 69. Their primary source of information was each woman's responses to a detailed questionnaire about her eating habits, use of nutritional supplements, and health-related issues, from body mass index to smoking to use of hormone replacement therapy. From that population sample, the researchers further focused on 152 women subsequently diagnosed with RA, validated by medical records.

Comparing the general dietary profiles and specific RA profiles, researchers found an inverse correlation between greater intake of vitamin D and RA risk. In other words, women whose diets were highest in vitamin D had the lowest occurrence of the disease. Interestingly, women who got their vitamin D primarily from supplements showed a stronger inverse association with RA development than did those whose vitamin D came mostly from rich food sources. Calcium consumption had no significant impact on the protective benefits of vitamin D.

"Vitamin D has immunologic activity independent of its crucial role in calcium regulation," asserts a member of the research team Linda A. Merlino, MS. Citing clinical observations, as well as numerous studies with animals, she notes how vitamin D has been shown to be synthesized into the synovial fluid of rheumatic joints and may also help regulate and normalize T cell activity.

"While the immunomodulatory effects of vitamin D are not yet fully elucidated, the results from this study suggest a possible role for vitamin D in reducing the risk of an immunologic disorder," concludes Kenneth G. Saag, MD, MSc., the senior investigator on the study. "These results are largely hypothesis generating; further studies will be required to corroborate or refute our findings."

The Importance Of Vitamin D

As women get older, surprisingly, estrogen deficiency becomes less important than vitamin-D deficiency. Vitamin D not only helps the body absorb calcium but must be present to block hormones that break down bone. Taking vitamin D and calcium together has been shown in studies to improve bone density more significantly after the age of 60. This is likely because many people over the age of 60 are vitamin-D deficient. Getting less sun exposure due to being less active is the likely explanation, along with dietary changes.