Metformin and Risk of Hypertension in Taiwanese Patients With Type 2 Diabetes Mellitus

Background-Whether metformin use may reduce hypertension risk has not been studied. This study investigated such possibility in patients with type 2 diabetes mellitus. Methods and Results-Newly diagnosed patients with type 2 diabetes mellitus during 1999-2005 were enrolled from the reimbursement database of the Taiwan's National Health Insurance and followed to December 31, 2011. Hypertension was defined either by a diagnosis or by a diagnosis plus the use of angiotensin converting enzyme inhibitors/angiotensin receptor blockers and/or calcium channel blockers. Analyses were conducted in a propensity score matched-pair cohort of 4810 ever users and 4810 never users. Cox proportional hazards regression model was used to estimate the hazard ratios. Results showed that when hypertension was defined by a diagnosis, 2261 never users and 1908 ever users developed hypertension. The overall hazard ratio was 0.724 (0.681-0.769) and the hazard ratios for the first (<2.0 months), second (2.0-13.0 months) and third (>13.0 months) tertiles of cumulative duration were 0.820 (0.745-0.903), 0.692 (0.634-0.756), and 0.687 (0.630-0.749), respectively. When cumulative duration of metformin therapy was treated as a continuous variable, the hazard ratio was 0.991 (0.989-0.994) for every 1-month increment of metformin use. When hypertension was defined by a diagnosis plus the use of antihypertensive drugs, the overall hazard ratio was 0.831 (0.771-0.895), the hazard ratios for the respective tertiles were 0.868 (0.769-0.980), 0.852 (0.767-0.946), and 0.787 (0.709-0.874), and the hazard ratio was 0.994 (0.991-0.997) for every 1-month increment of metformin use. Conclusions-A reduced risk of hypertension is observed in metformin users in a dose-response pattern.