Can't slice that orange? Moving to Florida might help.

RODALE NEWS, EMMAUS, PA—You feel tired and your joints ache, but the symptoms seem to come and go—and of course they’re never present when you visit the doctor. If this sounds like you, could be you’re suffering from rheumatoid arthritis, an autoimmune disease characterized by inflammation of joints and bone tissue that doesn't seem to have any known causes or definite risk factors. Even the symptoms can be hard to pin down.

"We simply don't know much about rheumatoid arthritis," says Nortin M. Hadler MD, professor of medicine and microbiology/immunology at the University of North Carolina at Chapel Hill, and attending rheumatologist at UNC Hospitals. "And it's certainly not for lack of trying." As researchers continue to investigate potential causes, they're turning to possible environmental factors that could trigger the onset of the disease. One study, published in a recent issue of the journal Environmental Health Perspectives, suggests that where you live could play a role.

THE DETAILS: The study authors used data from the long-running Nurse's Health Study, which began in 1976 and includes nurses living in all 50 states. Questionnaires provided information about where the nurses lived at the beginning of the study and where they've moved since, and whether they’ve been diagnosed with rheumatoid arthritis. The study authors gathered this information on 9,681 women.

There were significantly more women who had been diagnosed with rheumatoid arthritis while living in northern states than in southern and western states. The researchers also looked back to the nurses’ 1988 addresses to see where women with rheumatoid arthritis had been living before being diagnosed. Those addresses revealed an even higher risk for women in some of the northernmost regions of the country: northern Washington state near the Canadian border; the northernmost portions of Wisconsin and Michigan; northern Vermont, northern New Hampshire, and southern Maine. This suggests that rheumatoid arthritis risk was influenced more by where the nurses lived when they were younger, rather than where they lived when diagnosed, the authors write.

WHAT IT MEANS: While the study shows some pretty compelling data, says Dr. Hadler, it doesn't provide physicians with enough evidence to suggest that women at risk for the disease start moving south. "People have been looking for causes for years and we can't find one," he says. But he adds that geographic locale could influence onset of the disease, for instance, bacteria and viruses that could trigger an autoimmune response. There may be some type of rheumatoid arthritis–related bacteria that thrive up north but languish more the farther south and west you go, suggests Dr. Hadler, who wasn’t affiliated with the study. Or, the explanation could be even more basic. "It could just be that nurses are more willing to report and seek treatment for rheumatoid arthritis in colder climates, rather than in warmer climates, where it's easier to cope with," he says.