15 Surprising Facts About Rheumatoid Arthritis(15 Surprising Facts About Rheumatoid Arthritis )

About 1.3 million people in the U.S., or 1% of adults, have rheumatoid arthritis.

RA is different from osteoarthritis; it's caused by an abnormal immune reaction that attacks the lining of the joints and damages other parts of the body.

More research is needed to shed light on RA's exact causes, which are thought to be a combination of genes and environmental factors. However, here are some surprising facts about what is known about RA's history, triggers, and risk factors.

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RA used to be a "wasting disease"

In the past, people with RA were often rail-thin; exercise was thought to do further damage to the joints, so their muscles atrophied, says David Pisetsky, MD, professor of medicine and immunology at the Duke University Medical Center, in Durham, N.C. In addition, the chronic inflammation associated with RA causes weight loss and loss of appetite, he says.

Today, medicines curb inflammation, and exercise is part of treatment—so RA doesn't have to mean wasting away.

While exercise can be difficult (if not impossible) during a flare-up, activity is generally thought to help, not hurt, people with RA.

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Smoking may trigger RA

Smoking is the most well-understood environmental trigger and may play a role in one-third of severe cases of RA, including more than 50% of RA diagnoses among people who are genetically susceptible to the disease.

"Smokers who have a genetic variant known as shared epitope have a tenfold increased risk for developing RA," Dr. Pisetsky says. "We know smoking causes heart disease and certain cancers and many other diseases, but there is surprise about its link to RA."

RA risk varies with geography

The further you get from the equator, the higher your risk of RA. What's more, living at a higher latitude earlier in life——between ages 15 and 30——seems to be riskier than at other times.

In a 2010 study of nearly 10,000 women, RA risk was higher for those living in the Northeast and Midwestern United States, compared to women who lived west of the Rockies.

The authors note that the increased risk at higher latitudes could be due to lack of sunlight, as well as other environmental factors.