Obesity contributing to rise in RA

Cigarette smoking and obesity at any stage of life are associated with an increased risk for rheumatoid arthritis.

Obesity at any stage of life raises the risk of rheumatoid arthritis (RA).

Current and former smokers face an increased risk for developing rheumatoid arthritis.

A history of obesity raises the risk of rheumatoid arthritis by about 25%, according to a new retrospective, population-based study.

Of particular interest is that the researchers found that a “history of obesity”-not necessarily current obesity-raises the risk. In fact, obesity at incidence/index date did not reach statistical significance (odds ratio [OR], 1.10; 95% Confidence Interval [CI], 0.88–1.38), whereas a history of obesity, after adjusting for smoking status, did (OR 1.24; 95% CI, 1.01–1.53; P=0.041).

Published in Arthritis Care and Research (2012 Apr 18; doi: 10.1002/acr.21660. [Epub ahead of print]), the results indicate that the association between a history of obesity and development of RA was similar for both sexes, but was twice as strong for those <60 years of age (32% increase) as for those ≥60 years (15% increase).

During the period 1985 to 2007, incidence of RA rose by 9.2 per 100,000 women. According to the authors, obesity accounts for half (52%) of this increase, or 4.8 cases per 100,000 women.

Researchers from the Mayo Clinic looked at 813 Minnesota residents who fulfilled 1987 American College of Rheumatology criteria for RA and 813 comparable controls. The mean age of the participants was 56 years; 68% were female.

The researchers defined “obese” as a BMI ≥30 kg/m2. By this standard, almost one-third of the participants were obese (30% of RA group and 28% of controls). Forty percent of the RA group had a history of obesity versus 36% of the controls. The researchers did not collect information regarding the length of time participants were obese.

Although no association was found between either a history or presence at incidence/index data of being underweight (BMI <20 kg/m2) or overweight (BMI 25 to 29 kg/m2) and the development of RA, both current and former cigarette smoking increased the risk of RA by 48% and 40%, respectively. The authors caution that smoking cannot explain the recent rise in the incidence of RA because the number of people who smoke has decreased.

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