Mortality after bariatric surgery had been studied earlier, but selection bias, amplitude of follow-up visits have hindered the inference of results. This population-based matched cohort study was aimed to determine the association between bariatric surgery and all-cause mortality. The study took place in Ontario, Canada, involving 13,679 patients who underwent bariatric surgery from January 2010 to December 2016, and 13,679 matched nonsurgical patients. After 4.9 years, the mortality rate was 2.5% in the non-surgery group and 1.4% in the surgery group.

The patients aged 55 years or more had a risk reduction of 3.3%, with a lower HR of mortality in the surgery group. Observed relative effects were similar across sex; however, the observed association in absolute terms was more significant in men. The primary outcome measure was all-cause mortality, with cause-specific mortality as the secondary outcome. Cause of death was classified into cardiovascular, oncologic, other medical and external.

Among well-matched patients in a single-payer public health care system with complete follow-up data, bariatric surgery was associated with lower observed mortality after 4.9 years of follow-up. This observed lower association in overall mortality was mediated mainly through lower observed cardiovascular and cancer mortality. Moreover, men and patients aged 55 years or older had the largest absolute associations between bariatric surgery and lower mortality.