Background/Purpose: There are diverging results on the relation between body mass index (BMI) and risk of rheumatoid arthritis (RA). From a previous nested case-control study, based on a population based health survey performed in 1974-1992, we reported a reduced risk of RA in men with high BMI, whereas BMI did not affect RA development in women. The purpose of the present study was to investigate the impact of BMI on the risk of RA in a later population based survey performed in the same area.

Methods: Between 1991 and 1996, 30447 subjects (12121 men; 18326 women) were included. Height and weight were measured, and alcohol exposure was assessed using a diary, completed during 7 consecutive days, and classified as low/moderate/high intake. From this population, we identified individuals who developed RA after inclusion by linkage to 4 different RA registers. In a structured review of the medical records, patients were classified according to the 1987 American College of Rheumatology criteria for RA. Four controls for each validated case, matched for sex, year of birth and year of screening, who were alive and free of  RA when the index person was diagnosed with RA, were selected from the health survey database. The impact of BMI on the risk of RA was examined in conditional logistic regression models, stratified by sex. Models including alcohol use were restricted to individuals classified as adequate reporters of total energy intake based on previous studies, and adjusted for total energy intake.

Results: A total of 172 patients (36 men/136 women, mean age at RA diagnosis 63 years) were diagnosed with RA after inclusion in the health survey. The median time from inclusion to RA diagnosis was 5 years (range 1–13). Seventy-nine cases (24 men/55 women) had been included in the previous survey. There was no difference in BMI between women who subsequently developed RA and controls [mean 25.9; standard deviation (SD) 4.9 vs. 25.6 (SD 4.4) kg/m²; odds ratio (OR) for RA development 1.09 per SD; 95 % confidence interval (CI) 0.88-1.35]. By contrast, men with a diagnosis of RA during the follow-up had a lower BMI at baseline compared to controls [mean 24.6 (SD 3.1) vs. 26.5 (SD 3.5) kg/m²; OR 0.47 per SD (95 % CI 0.29-0.76)]. The negative association between BMI and RA development in men remained significant in separate models adjusted for smoking (p=0.007) and level of formal education (p=0.034), and adjustment for alcohol intake did not lead to major change in the estimated effect of BMI (OR 0.57; 95 % CI 0.30-1.09). Similar adjustments had no significant impact in women. For pre-RA cases who participated in both surveys, the mean time between BMI measurements was 12.4 years in men and 8.7 years in women. Among these subjects, there was on average a slight decrease in BMI in men (mean change -0.06 kg/m² per year; 95 % CI -0.27 to 0.15) and a slight increase in women (mean change 0.14 kg/m² per year; 95 % CI -0.25 to 0.53).

Conclusion: BMI was negatively associated with future RA development in men. This pattern did not appear to be explained by differences in smoking, education or alcohol use. There were no major changes in BMI over time in cases who later developed RA. Hormonal factors related to adipose tissue may reduce the long term risk of RA in men.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/high-body-mass-index-is-associated-with-a-reduced-long-term-risk-of-rheumatoid-arthritis-in-men/