RA is not the same as osteoarthritis, which develops with age or with wear-and-tear on the joints. RA occurs much less often, but is usually more severe. RA and lupus are both autoimmune disorders.
The researchers tracked nearly 185,000 women for up to 24 years. Overall, they found no clear relationship between the women's estimated intake of antioxidants -- including vitamins A, C and E and beta-carotene -- and their likelihood of being diagnosed with RA or lupus.
The findings contradict hints from earlier research that women with higher intake of antioxidants might have lower risks of developing these diseases.
One reason for checking whether antioxidants in the diet would have an effect is that people with RA and lupus have lower antioxidant levels in their blood than healthy individuals. And studies in mice have shown that giving antioxidants helps reduce the type of immune-system-triggered inflammation that's associated with these diseases.
Not only do antioxidants help control inflammation, but they also protect body tissue from potentially cell-damaging particles called reactive oxygen species.
But in the new study reported in the American Journal of Epidemiology, researchers found no link between the women's reported antioxidant intake and their risk of developing RA or lupus. The women were participating in the Nurses' Health Study and Nurses' Health Study II, two large projects that have tracked lifestyle factors and disease risk among nearly 240,000 U.S. women since 1976 and 1989, respectively.
The study had its limitations -- including the fact that it was observational. The researchers merely asked the women about their antioxidant intake and then observed what happened to them over time, so the outcomes may just be coincidental. A study in which participants are randomly assigned to take antioxidant supplements or not, then have their RA and lupus rates followed over time, would provide stronger evidence as to whether the nutrients affect the risk of developing the diseases.
Nor can the findings exclude the possibility that significant deficiency in certain antioxidants might play a role in RA or lupus risk, note the researchers, led by Dr. Karen H. Costenbader of Brigham and Women's Hospital in Boston.
Lupus -- known formally as systemic lupus erythematosus -- involves painful, swollen joints, fatigue and skin rash, but it can also damage other parts of the body, including the heart and blood vessels. RA arises when the immune system mistakenly attacks joints all over the body, leading to inflammation, pain and progressive joint damage.
Costenbader's team focused on 184,643 women who were free of RA or lupus at the outset and had completed detailed questionnaires on their diets and supplement use starting in 1980 or 1991, depending on the study.
The researchers used those reports to estimate the women's daily intakes of vitamins A, C and E, as well as alpha- and beta-carotene, lycopene, lutein, beta-cryptoxanthin and zeaxanthin.
Between 1980 and 2004, 787 women were newly diagnosed with RA, while 192 were diagnosed with lupus.
Women with higher antioxidant intakes did tend to maintain a healthier lifestyle overall, the study found. They were generally more physically active and less likely to smoke, for example. When those factors were taken into account, antioxidant consumption itself showed no strong relationship to RA or lupus risk.
This finding, of course, does not negate the importance of eating antioxidant-rich foods for one's overall health. Foods high in the antioxidants assessed in this study include citrus fruits, leafy greens like spinach and kale, cruciferous vegetables like broccoli and Brussels sprouts, and red or orange fruits and vegetables like carrots, watermelon and sweet potatoes.
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