Women with rheumatoid arthritis are already more prone to heart attacks than the general population because of their autoimmune disease.
The study by the Mayo Clinic, which was published in the April edition of Arthritis Care & Research, found the risk of getting rheumatoid arthritis was about 20 percent more for women who were overweight.
The researchers followed 813 patients with rheumatoid arthritis and the same number of controls. They also studied other patient data from 1980 to 2007 and found that from 1985 to 2007 the incidence of rheumatoid arthritis rose 9.2 percent per 100,000 women. Obesity accounted for 52.2 percent of the increase.
Rheumatoid arthritis is an inflammatory disease that causes pain, swelling and stiffness in the joints and surrounding tissues. About 1.3 million people in the United States have the disease, which occurs in two to three times as many women as men, according to the National Institutes of Health.
Obesity is blamed for myriad health problems, including diabetes, high blood pressure, stroke, some forms of cancer, sleep apnea, gallbladder disease and osteoarthritis. Rheumatoid arthritis will likely be added to the list.
"We'll be paying more attention to their weight," said Dr. Nadera Sweiss, director of rheumatology clinical research and the Cold Hand Clinic at the University of Illinois Hospital and Health Sciences System.
"We (already) try to counsel patients with rheumatoid arthritis about other risk factors for heart disease like smoking, high blood pressure, high cholesterol," Sweiss said.
Sweiss pointed out that an article in the May edition of the Annals of the Rheumatic Diseases showed a link between obesity and psoriatic arthritis, a type of arthritis that occurs in the joints.
Dr. James Grober, a rheumatologist with NorthShore University HealthSystem in Evanston, said there had been growing evidence that fat tissue was a source of inflammatory mediators. He said the disease was likely caused by a combination of genetic susceptibility and predisposition and some other factor. The Mayo study mentions that rheumatoid arthritis may be associated with chronic inflammation, vitamin D deficiency and sex hormones, as well as risk factors like smoking and oral contraceptives.
"I think I was surprised at the magnitude of the apparent influence of obesity on the risk of rheumatoid arthritis," Grober said.
Dr. Eric Matteson, who wrote the study with Cynthia Crowson, Dr. John Davis III and Dr. Sherine Gabriel, said they had wanted to find the reasons behind an increase in rheumatoid arthritis in the past two decades. They realized obesity had also increased in that time period.
"The biological connection is we know that fat cells produce inflammatory proteins and they're active in inflammation," said Matteson, who chairs the rheumatology department at the Mayo Clinic.
"Your risk is still not huge of getting rheumatoid arthritis, but it's increased by that much more if you are overweight, so that's not trivial when you think of how many people in this country have rheumatoid arthritis," he said.
More people with rheumatoid arthritis could place a further burden on underserved individuals, as well as the country's health system, according to Sweiss, who sees many patients with the disease who are poor, smoke cigarettes, and don't have healthy diets or exercise regularly. She noted that, once the illness becomes severe, the medications needed — like Orencia or Humira — cost several thousand dollars monthly.
"This has a huge economical impact, especially since we're living in a time of economic crisis and it may be hard for patients to afford medications," Sweiss said.