Objective: There are conflicting reports concerning metformin use and mortality rates in patients with type 2 diabetes (T2DM). The aim of this study was to examine the relationship between metformin use and all-cause mortality in veterans with T2DM.
Research design and methods: An observational cohort study involving 2206 patients with T2DM was performed using computerized database from the Veterans Affairs Medical Center, Memphis, TN. All-cause mortality was compared among cohorts of metformin and nonmetformin users. Univariate and multivariate Cox regression models were used to estimate hazard ratios (HR) for all-cause mortality after adjusting for age, race, baseline estimated glomerular filtration rate, glycosylated hemoglobin, use of insulin, use of ACE inhibitors or angiotensin II receptor blockers or statins.
Results: The average length of follow-up in metformin and nonmetformin users was 62 ± 17 and 61 ± 18 months, respectively. The mean age was 63 ± 11 years. Crude mortality rates were similar in both groups: 266 (22%) metformin users and 253 (25.3%) nonmetformin users died. There was a trend for improved survival with metformin use (unadjusted HR 0.85, P = 0.07). After multivariate adjustment, metformin users had significantly decreased HR for time to all-cause mortality compared with nonmetformin users (adjusted HR 0.77, P < 0.01). Insulin use was an independent predictor of worsened survival in both univariate and multivariate analyses. In subgroup analysis of patients exposed to insulin, all-cause mortality remained decreased in metformin users (adjusted HR 0.62, P < 0.04).
Conclusion: Treatment of T2DM with regimens containing metformin alone or in combination with other hypoglycemic agents was associated with reduced all-cause mortality compared with regimens without metformin.