ROME (FRONTLINE MEDICAL NEWS) – Obese people had a 50% increased rate of developing rheumatoid arthritis compared with normal or underweight people, in a case-control study of more than 2,000 Swedish residents for which researchers used prospectively collected data.

The increased rate of developing rheumatoid arthritis (RA) conferred by obesity occurred in both women and in men, it was greatest in the subgroup of people who developed RA symptoms when they were age 50 years or younger, and it was greatest in the subgroup of people seropositive for anti-citrullinated protein antibodies (ACPA), rheumatoid factor (RF), or both Dr. Lotta Ljung said at the European Congress of Rheumatology.

The findings add to the growing body of evidence documenting obesity as a risk factor for development of RA, said Dr. Ljung, a rheumatologist at Umeå (Sweden) University.

She and her associates used data collected in two Swedish population-based cohorts followed prospectively, the V ä sterbotten Intervention Programme and the Northern Sweden portion of the MONICA project. The two databases included baseline and long-term follow-up data during 1985-2013 from more than 110,000 Swedish citizens, average age 52 years at baseline, and average body mass index of 26 kg/m2. The databases included 557 patients with incident RA, which appeared an average of 6 years following entry into their database, with 83% of the cases showing seropositivity for ACPA, RF, or both. The researchers matched these cases on a 3:1 basis with 1,671 controls without RA by their sex, year of birth, cohort, examination year, and region of residence in Sweden.

In an analysis that controlled for both smoking and education level, people who entered one of the databases with a BMI of 30 kg/m2 or higher, defined as obesity, had a statistically significant 50% increased rate of developing RA during follow-up, compared with people who entered with a BMI of less than 25 kg/m2, which corresponded to normal- or under-weight. Those with a BMI of 25-29.99 kg/m2, the overweight group, had a borderline statistically significant 20% increased rate of developing RA during follow-up, compared with the reference group, Dr. Ljung reported .

An analysis that examined the link between incident RA and baseline BMI as a continuous variable showed a 2% increased rate of incident RA for each 1-unit increase in BMI, but this relationship fell short of statistical significance after adjustment for smoking and education level. A second analysis that looked at waist circumference as a continuous variable showed a statistically significant 2% rise in RA incidence for each 1-cm increase in waist circumference at baseline after adjustment.

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