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 treatmentso 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."
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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 lifeat ages 15 and 30seems 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.
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Vitamin D may be linked to risk
A 2004 study tracked more than 29,000 women and found that those with the lowest intake of vitamin D had the highest risk of developing RA.
It's not proven that the vitamin plays a role. However, a protective effect of vitamin D could explain why people who live at higher latitudesand get less of the vitamin in general because sunlight triggers its production in the bodyseem to be at higher risk of RA. What's more, other autoimmune diseases, such as multiple sclerosis, have been tied to vitamin D intake.
More studies are needed to confirm the link.
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Traffic pollution may play a role
Pollution through particulates (microscopic particles that can be inhaled deep into the lungs) is linked with inflammation, so Harvard researchers conducted a 2009 study of more than 90,000 U.S. women that looked at the relationship between RA and traffic pollution.
They found that women who lived within 0.031 miles of a major road had the highest risk of RA, compared with those who lived farther away.
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RA is on the rise among women
RA is on the rise among U.S. women for the first time in 40 years, according to a 2010 study from researchers at the Mayo Clinic, in Rochester, Minn.
They found a 2.5% increase in the rates of RA among women between 1995 and 2007, while rates among men dropped over that period.
It's not clear why. But researchers speculate that it may be due to cigarette smoking (women aren't quitting as quickly as men); lower-estrogen birth control pills (the hormone may be protective); and, possibly, more vitamin D deficiencies.
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RA's history is murky
"RA doesn't exist in mummies, and there is no evidence that it existed in the Old World before Christopher Columbus discovered America in 1492," says Martin J. Bergman, MD, the chief of the division of rheumatology at Taylor Hospital, in Ridley Park, Pa.
"This suggests it may be caused by an environmental factor, but that has never been proven," he says.
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Depression and RA travel together
RA and depression are often linked.
"This is probably related to the pain of RA and the stress associated with living with a chronic illness," Dr. Bergman says. "But high levels of the inflammatory protein tumor necrosis factor alpha (TNF-a) in the blood have been associated with depression, so it is possible that the inflammation causing the RA also causes depression."
Many of the drugs that treat RA block TNF.
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RA means other autoimmune diseases too
"People who get autoimmune diseases like RA have genetic risk factors that make them susceptible to autoimmunity in general," says Dr. Pisetsky.
Autoimmune thyroid diseases and Sjögren's syndrome (a dry eye and mouth disease) are particularly common in people with RA.
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Pregnancy affects RA symptoms
Some autoimmune diseases, including RA and lupus, get better during pregnancy.
"RA often goes into remission during pregnancy," Dr. Pisetsky says. Some stats show that up to 75% of women with RA will go into remission by about the second month of pregnancy. "It can flare up after delivery though," he says.
Pregnancy may dampen your otherwise overactive immune system, and some of the hormones that increase during pregnancy may also be protective.
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RA's heart-attack risk on par with diabetes
RA can dramatically increase your heart-attack risk.
"This is not appreciated, but RA is an independent risk factor for heart attacks, even if your cholesterol level is normal, your blood pressure is low, and you don't have diabetes," Dr. Bergman says. "If you have active RA, you are at two- to threefold increased risk for heart attack."
The systemic inflammation that is a hallmark of RA is the likely culprit, he says.
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RA linked to fibromyalgia, too
Approximately 20% to 30% of people with RA also have fibromyalgia.
However, research suggests that people who drink alcohol are at a lower risk of RA than those who do not.
"Moderate alcohol is anti-inflammatory and a drink a day for women and one or two drinks a day for men may reduce risk for developing RA," Dr. Bergman says. "The only thing I caution is to make sure it doesn't interact with other drugs; the big ones are methotrexate and leflunomide."
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RA and diabetes: It's complicated
The inflammation of RA may increase the risk of developing type 2 diabetes.
Corticosteroids used to treat RA may also increase type 2 diabetes risk by increasing blood-sugar level, but other RA medications, such as the antimalarial drug hydroxychloroquine as well as anakinra (Kineret), may decrease risk of diabetes among people with RA.
RA and type 1 diabetes, which is also an autoimmune disorder, share some of the same genetic risk factors and inflammation markers.
"The RA and diabetes connection is an interesting story," says Dr. Pisetsky.
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RA is linked to lung disease
"Lung diseases can be extremely common in RA," says Aryeh Fischer, MD, an associate professor of medicine at the National Jewish Health Autoimmune Lung Center, in Denver. Serious lung disease is less common, but about half of RA patients have subclinical lung disease, he adds.
With RA, airways can become inflamed, too, and drugs such as TNF blockers may up the risk of tuberculosis. RA may also double the risk of COPD.
Smoking may be behind the RA–lung disease link: A major risk factor for RA, smoking also ups lung disease risk.
Researchers, including Dr. Fischer, are studying whether RA starts in the lungs.
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