Metformin reduces risk of varicose veins in patients with type 2 diabetes

Aim This population‐based retrospective cohort study compared the incidence of varicose veins in an unmatched cohort and a cohort of 1:1 propensity score (PS)‐matched pairs of ever and never users of metformin in type 2 diabetes patients. Methods Patients with new‐onset type 2 diabetes during 1999 to 2005 were enrolled from Taiwan's National Health Insurance and followed until December 31, 2011. Analyses were conducted in an unmatched cohort of 123 710 ever users and 15 095 never users and in 15 088 PS‐matched pairs of ever users and never users. Hazard ratios were estimated by Cox proportional hazards model incorporated with the inverse probability of treatment weighting using the PS. Results New‐onset varicose veins were diagnosed in 126 never users and 633 ever users in the unmatched cohort and in 126 never users and 80 ever users in the matched cohort. The respective incidences were 191.36 and 110.04 per 100 000 person‐years in the unmatched cohort and 191.41 and 115.81 per 100 000 person‐years in the matched cohort. The hazard ratio for ever versus never users in the unmatched cohort was 0.57 (95% confidence interval, 0.47‐0.69) and was 0.60 (0.45‐0.80) for the matched cohort. In the unmatched cohort, the hazard ratios for the first, second, and third tertiles of cumulative duration were 1.03 (0.83‐1.28), 0.55 (0.44‐0.69), and 0.29 (0.23‐0.37), respectively. The respective hazard ratios in the matched cohort were 0.97 (0.65‐1.43), 0.79 (0.55‐1.15), and 0.24 (0.13‐0.42). Conclusion Metformin use is associated with a lower risk of varicose veins in patients with type 2 diabetes.