Effects of oral contraceptives on rheumatoid arthritis in Korean menopausal women: A nationwide cross-sectional study

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease with a multifactorial etiology. The higher prevalence of RA in women than in men may originate from differences in sex hormone levels or types. Ethnicity may interact with hormonal factors to produce various observed differences in the prevalence of RA. Oral contraceptives (OCs) are a source of exogenous sex hormones and can affect the prevalence of RA. We investigated the effects of OCs on RA in Korean menopausal women using a national data set. Data were collected from a cross-sectional study of 8789 eligible participants who completed the 2008-2012 Korea National Health and Nutrition Examination Survey. To balance the distribution of baseline characteristics between those participants who had ever used OCs and those who had not, we employed propensity score matching to adjust for differences. We calculated odds ratios (ORs) and 95% confidence intervals (CIs) for the effects of OCs on the incidence of RA. The development of RA in Korean women rapidly increased during the perimenopause. After propensity score matching, the use of OCs was associated with RA (OR 1.24, 95% CI 1.01-1.51, P = 0.04). However, hormone replacement therapy (HRT) was not associated with RA regardless of whether OCs had been used (OR 0.80, 95% CI 0.62-1.04, P = 0.09, and OR 1.00, 95% CI 0.66-1.52, P = 0.99, respectively). Our findings suggest that factors associated with sex hormones influence the prevalence of RA.