Doctors have known for some time that people with rheumatoid arthritis (RA) are at higher risk of developing cardiovascular disease. Specifically, people who have RA have a 50% to 70% higher risk for cardiovascular disease than others and almost half of all adults with heart disease also have arthritis. Scientists think there are several factors in the relationship between RA and heart disease, but the primary suspect has to do with inflammation — inflammation is a risk factor for heart disease and RA is an inflammatory disease.
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Because diabetes is also classified as a disease with inflammatory characteristics, researchers have wondered if people with RA are at a higher risk of diabetes in the same way that they’re at a higher risk of heart disease. Previous studies looking into the relationship between RA and diabetes have been inconsistent, but now a new study involving over 100,000 patients has thrown new light on the question.
The research team, which was led by Seoyoung C. Kim, MD, Associate Professor of Medicine at Brigham and Women’s Hospital in Boston, set out with the hypothesis that RA patients would have a higher risk of developing diabetes than non-RA patients. As Kim explained, certain factors involved in RA can disrupt “insulin-signaling pathways,” which might then lead to insulin resistance. “Therefore,” she said, “the risk of type 2 diabetes mellitus, which is a traditional CVD [cardiovascular disease] risk factor, may be increased in RA and could be a target for intervention to reduce CVD-related mortality.” The researchers also wanted to look into the diabetes risk in patients with osteoarthritis, psoriatic arthritic and hypertension (high blood pressure).
Using information retrieved from a large commercial health claims database, they identified 108,568 subjects with RA. They matched these patients with an equal number each of non-RA patients and of patients with hypertension and osteoarthritis. The subjects’ average age was 55.6 years, except for those with psoriatic arthritis (48.6 years). About three out of four were women, except in the psoriatic arthritis group, where the split was about 50-50.
The researchers concluded that patients with RA did not have a higher risk of diabetes. The chances that a subject would develop type 2 diabetes was about 24% to 35% lower in the RA group than in the hypertension, osteoarthritis and psoriatic arthritis groups. During the follow-up period, which last about one-and-a-half to two years, it was found that diabetes rates were highest in the hypertension and psoriatic arthritis groups. The lowest diabetes rates were in the RA group. As the researchers put it, “While systemic inflammation in RA is thought to increase the risk of CVD and cardiovascular risk factors such as diabetes mellitus, our findings suggest that having RA itself does not confer an increased risk of type 2 diabetes mellitus.”
Why the differences? The researchers could not say for certain, but they speculated that the pervasive use of biologic therapies for RA might play a role because it’s been confirmed that these therapies lower the risk of diabetes when compared with nonbiologic therapies. That the osteoarthritis group showed higher rates of diabetes might be due to the higher prevalence of obesity in that group. Kim concluded, “While systemic inflammation in rheumatoid arthritis increases the risk of cardiovascular disease, our findings unexpectedly show that having rheumatoid arthritis itself does not confer an increased risk of type 2 diabetes compared with four different comparator groups. Since all rheumatoid arthritis patients included in our study were treated with at least one disease-modifying antirheumatic drug, our study is unable to test the association between no treatment or undertreatment for rheumatoid arthritis and risk of type 2 diabetes.”