Association of statins with diabetes mellitus and diabetic complications: role of confounders during follow-up.

Studies have associated statin use with increased risk of diabetes and diabetic complications. These studies often ensure comparability of statin users and non-users at baseline; however, most studies neglect to consider confounders that occur during follow-up. Failure to consider these confounders, such as new medications or procedures, may result in identification of a spurious association between statins and outcomes. The objective of this study was to examine the association of statins with diabetes mellitus and diabetic complications; and to examine potential confounders during the follow-up period that might affect this relationship. We conducted a retrospective cohort study using Tricare data (from October 1, 2003 to March 31, 2012). We propensity score-matched statin users and non-users on 115 baseline characteristics before starting statins; these characteristics would be potentially associated with the use of statins or the outcomes of interest. Outcomes included the risk of diabetes mellitus and diabetic complications. Out of 60,455 patients (10,910 statin users and 49,545 non-users), we propensity score-matched 6728 statin users to 6728 non-users. Statin users had higher ORs for diabetes (OR 1.34, 95% CI 1.24 to 1.44) and diabetes with complications (OR 1.28, 95% CI 1.16 to 1.42). Adjustment for potential confounders that occurred during the follow-up period did not explain or diminish the association between statins and adverse outcomes. Statin users in comparison to similar non-users were more commonly diagnosed with diabetes and diabetic complications, even after adjustment for potential confounders that occurred during the follow-up period.