Obesity May Be a Risk Factor for Developing Rheumatoid Arthritis
Being obese could increase the risk of developing rheumatoid arthritis by 20 percent.
Smoking has long been considered the only modifiable risk factor that increases a person’s chances of developing rheumatoid arthritis (RA), an autoimmune disease causing pain, swelling and potential deformity in affected joints. Now doctors from the Mayo Clinic in Rochester, MN., say obesity also increases the odds of developing RA – at least for women, who are two to three times more likely than men to have the disease.
“This is really new. Smoking, and now it looks like obesity, appear to be factors for risk,” says Eric Matteson, MD, co-author of the study published online in Arthritis Care & Research that examined the link between obesity and RA. Dr. Matteson is chair of the Mayo Clinic’s division of rheumatology.
While no one knows for sure what causes this disease, a genetic predisposition is likely – especially in combination with environmental factors, such as previous infection, occupational exposure and smoking. As for obesity as a risk factor, the evidence has been contradictory. (However, weight gain can occur after diagnosis due to certain medications, a decrease in physical activity and/or a change in body composition due to RA.)
For this study, researchers compared medical records from 813 RA patients in the Rochester Epidemiology Project (which consists of data from RA patients in Olmsted County, Minn., gathered between 1980 and 2007) with the medical records of 813 participants (matched for age, sex and other factors) without the disease, who served as a control group. Nearly 70 percent of study participants were women, and about 30 percent of each group was classified as obese (with a body mass index of 30 or greater) when they entered the study.
The researchers write that after four decades of decline, the number of RA cases in Olmsted County started to rise again in 1995. While they note that the cause of the rise is unknown, they surmise it must be due to changes in environmental risk factors, as genetic factors do not change so quickly. While the “list of potential environmental influences on development of RA is extensive,” they chose to focus on obesity “due to its recent, dramatic increase in prevalence.”
To determine if there was a relationship, they calculated the proportion of RA cases that could likely have been prevented by eliminating obesity. They found that obesity explained more than half (52 percent) of the increase in RA among women between 1995 and 2007. Dr. Matteson says he can’t exclude the possibility that obesity could be a risk factor for RA in men, but his team didn’t have enough data from male patients to say that for sure.
The study places obesity as a more modest risk factor for RA than smoking, but a risk factor nonetheless. “Smoking would approximately more than double your risk of developing arthritis. Being overweight would add about 20 percent to that risk,” Dr. Matteson says.
He notes the increased risk for developing RA existed for people who had ever been obese – not just those who were obese when they got RA.
Rheumatologists often stress the importance of weight loss to their patients – extra weight contributes to joint damage, not just discomfort, and it reduces function. But this new research adds more evidence to the importance of weight loss for the entire population.
“Now we have another compelling reason to stress the importance of weight control: being overweight increases your risk for getting RA, just as being overweight increases your risk for other diseases, like heart disease, hypertension and diabetes,” says Dr. Matteson. “It’s yet another reason to really try to keep your weight ideal throughout your lifetime.”
As for why obesity appears to increase the risk of developing RA, Dr. Matteson’s team didn’t specifically study causes, but he believes there could be a variety of explanations.
“There are several biological reasons. One is that fat cells actually produce inflammatory proteins,” Dr. Matteson says. “Another is that we know people who are overweight have lower vitamin D levels generally, and that has been associated with RA.”
Scott Kahan, MD, director of the National Center for Weight and Wellness in Washington, D.C., says one downside of this study – which the researchers acknowledge in their paper – is that the study population from Olmsted County is 90 percent white, which makes it difficult to know if these findings apply to other ethnicities. But he says most scientific research has limitations and these findings are interesting.
“With this study it gives a little more data than what we’ve had in the past,” Dr. Kahan explains. He also says it adds to the big picture of the importance of being a healthy weight.
“The bottom line is that we have a whole lot of reasons why excessive weight can be destructive to our health,” Dr. Kahan says. “Ultimately we need to continue to figure out how on a personal level we can address our weight and health over time. And we have to figure out on a policy level how we can continue to support people’s healthy decision-making.”
To people who are obese and have already developed RA, Dr. Matteson has this message: “It’s not too late at all [to lose weight]. There’s some evidence that drugs that we use to treat RA don’t work quite as well in people who are overweight,” he explains, adding that you will most likely experience a variety of benefits by getting down to a more ideal weight. “The other reason it’s not too late is because when you lose that weight you are doing your joints a big favor. Your joints will thank you; they will last you longer.”