Association between statin exposure and diabetes incidence among privately-insured patients before and after applying a novel technique to control for selection bias

Abstract

IntroductionThe association between statins and incident diabetes mellitus (DM) in observational studies is much larger than that reported from randomized controlled trials. We sought to assess this association using a novel design controlling for selection bias. MethodsUsing data from MarketScan, we identified a cohort of non-diabetic patients who initiated a statin and matched them to patients not taking statins. From the statin-user cohort, we identified two subgroups: patients who received statin refills for >6 months (continuers) and patients who received statin refills <6 months (discontinuers). Patients were followed for a minimum of two years to determine incident DM. ResultsWe included 442,526 patients, divided equally between statin users and non-users. Statin use was associated with increased DM (9.9% vs. 4.4%, HR 2.2, p < 0.001). Among the 221,263 statin users, there were 194,357 continuers and 26,906 discontinuers. There was no significant difference in the incidence rate of DM between both groups (10.0% vs. 9.3%, HR 1.03, p = 0.22). ConclusionsStatin use was strongly associated with incident diabetes when users were compared to non-users but not when continuers were compared to discontinuers. Selection bias confounds the association between statin use and incident diabetes in observational studies.