The association of obesity and the risk of rheumatoid arthritis according to abdominal obesity status: a nationwide population-based study in Korea

ObjectivesThis study aimed to assess the association between obesity or changes in body mass index (BMI) and the risk of RA considering the abdominal obesity status.MethodsWe included individuals aged 23 to 60 who underwent a national health examination in 2012-2013 (baseline) and four years prior. Obesity was defined by a BMI >= 25 kg/m2. The change in BMI over 4 years was divided into quartiles. Cox proportional hazard analysis was performed to assess the association of obesity and BMI change with the risk of RA.ResultsA total of 6,207,246 subjects were included, and 7,859 incident cases of RA were identified. Obesity was associated with a reduced risk of RA in males (HR 0.78, 95% CI 0.71-0.85) and females (HR 0.91, 95% CI 0.85-0.97). In subgroup analysis according to abdominal obesity status, the associations were observed for obesity with normal waist circumference (WC) in males (HR 0.75, 95% CI 0.67-0.84) and females (HR 0.88, 95% CI 0.81-0.95). In terms of BMI change, compared to the stable BMI group (quartile 2), the third (HR 0.92, CI 0.85-0.99) and highest quartile (HR 0.89, CI 0.83-0.96) showed an inverse association with the risk of RA in females, particularly in those with normal WC.ConclusionObesity was associated with a lower risk of RA, especially among individuals with a normal WC. Increased BMI was also associated with a lower risk of RA, but this association was mainly observed in females and specifically for those with normal WC.