Background/Purpose: Smoking is an established risk factor for rheumatoid arthritis (RA), and there is also evidence for an association with socioeconomic factors. As RA is more common in women compared to men, most studies of disease predictors have mainly included women, and data on risk factors in men are limited. Some studies indicate an increased risk of RA in women with high body mass index (BMI), whereas a negative association between BMI and future RA development in men has been reported. The purpose of this study was to investigate BMI, other anthropometric factors, smoking and level of formal education as potential predictors of RA in middle-aged men and women.

Methods: A nested case-control study was performed including participants in a population-based survey performed in 1991-1996. Cases diagnosed with RA from inclusion until December 2016 were identified through register linkage and validated in a structured process. Four controls for each case, matched for sex, year of birth, and year of inclusion, were included. Height and weight were measured as part of the health survey, and BMI was calculated as weight (in kg)/height (in m)2. Waist was measured as the circumference (cm) between the lowest rib and the iliac crest. Hip circumference (cm) was measured as the largest circumference between waist and thighs. Waist/hip ratio (WHR) was defined as the waist circumference divided by the hip circumference. Information on lifestyle habits and socioeconomics was collected using a self-administered questionnaire. Logistic regression analysis, taking into account the matched design of the study, was applied to investigate the relation between these exposures and risk of RA diagnosis during the follow-up.

Results: There were 305 incident cases of RA (232 women, 73 men), with a mean time from screening to diagnosis of 12 years. The mean age at inclusion in the survey for those diagnosed with RA during the follow-up was 56.8 years, and similar in women and men (Table 1). These cases were compared to 1220 matched controls (Table 1).In men, higher BMI was associated with a reduced risk of RA (odds ratio [OR] 0.63 per standard deviation [SD]; 95% confidence interval [CI] 0.46-0.87). There was also a trend towards a lower waist circumference among men who subsequently developed RA (Table 2), and a significant negative association with the WHR (OR 0.68 per SD; 95% CI 0.51-0.93). No associations between anthropometric measures and RA risk were found in women (Table 2). However, smoking and a low level of formal education were predictive of RA in women, but not in men (Table 2).

Conclusion: Anthropometric measures seem to have differential effects on the risk of RA in women and men. The inverse association between BMI and RA risk in men is supported by a similar relation with WHR. This suggests distinct underlying mechanisms related to abdominal obesity in men and women. Female smokers and women with limited education had an increased risk of RA, whereas no similar associations were observed in the smaller subset of men in this study.

Table 1.

Table 2.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sex-specific-associations-of-anthropometrics-smoking-and-eduction-with-the-risk-of-rheumatoid-athritis-a-nested-case-control-study/