Metformin use and long-term risk of benign prostatic hyperplasia: a population-based cohort study

OBJECTIVE: To assess whether metformin use affects risk of benign prostatic hyperplasia (BPH) by comparing the risk of BPH in men with type 2 diabetes who initiated first-line treatment with either metformin or sulfonylurea monotherapy between 2000 or 2006 in Northern Denmark. In this period, sulfonylurea and metformin were both frequently used as first-line glucose-lowering drug (GLD) treatment. DESIGN: A population-based cohort study. SETTING: Northern Denmark. PARTICIPANTS: All men who filled at least two prescriptions for metformin or for sulfonylurea, respectively, during their first 6 months of GLD treatment. Follow-up started 6 months after treatment start. PRIMARY OUTCOME MEASURES: Rates of subsequent BPH, identified based on community prescriptions for BPH-related treatment or hospital BPH diagnoses, and rates of transurethral resection of the prostate (TURP). Rates in metformin and sulfonylurea users were compared overall and stratified by 6-month haemoglobin A1c (HbA1c()) using Cox regression and an intention-to-treat (ITT) approach and an as-treated analysis. RESULTS: During follow-up, less than five persons were lost to follow-up due to emigration. In 3953 metformin initiators with a median follow-up of 10 years, the 10-year cumulative BPH incidence was 25.7% (95% CI 24.2 to 27.1). Compared with 5958 sulfonylurea users (median follow-up 8 years, 10-year cumulative incidence 27.4% (95% CI 26.2 to 28.6)), the crude HR for BPH was 0.83 (95% CI 0.77 to 0.89) and adjusted HR in the ITT analyses was 0.97 (95% CI 0.88 to 1.06). For TURP, the adjusted HR was 0.96 (95% CI 0.63 to 1.46). In the as-treated analysis, adjusted HR for BPH was 0.91 (95% CI 0.81 to 1.02). CONCLUSIONS: Compared with sulfonylurea, metformin did not substantially reduce the incidence of BPH in men with diabetes.