Periodontitis exposure within one year before anti-diabetic treatment and the risk of rheumatoid arthritis in diabetes mellitus patients: a population-based cohort study.

OBJECTIVE: To examine whether a history of periodontitis (PD) before anti-diabetic treatment is associated with risk of rheumatoid arthritis (RA) development in newly-treated diabetes mellitus (DM) patients. METHODS: We conducted a population-based retrospective cohort study using the 1997-2009 National Health Insurance (NHI) claims data of one million representative individuals from all NHI enrollees. Adults with DM (aged >/= 20 years) starting anti-diabetic treatment during 2001-2009 were classified as newly-treated DM patients. We identified 7097 DM subjects with PD history within one year before initiating anti-diabetes treatment (index date). By matching these 7097 subjects for age on the index date, sex, and year of the index date, we randomly extracted 14,194 DM subjects without PD history within one year before antidiabetic treatment. Adjusted hazard ratios (aHRs) with a 95% confidence interval (CI) were calculated by applying Cox proportional hazards models to quantify the association between PD history and RA risk. RESULTS: Compared with DM patients without PD exposure within one year before anti-diabetic treatment, crude HR and adjusted HR of RA among DM patients with PD exposure within one year before anti-diabetic treatment were 4.51 (95% CI, 1.39-14.64) and 3.77 (95% CI, 1.48-9.60). CONCLUSION: PD exposure within one year before anti-diabetic treatment was associated with increased RA risk in newly treated DM patients. The lack of knowledge about individual smoking status is a major limitation of this study.