Association Between Bariatric Surgery and the Long‐Term Risk for Venous Thromboembolism: A Population‐Based Matched Cohort Study

Obesity is a known risk factor for venous thromboembolism (VTE), but the long-term effect of weight-loss interventions such as bariatric surgery on VTE risk is uncertain. We conducted a population-based matched cohort study using administrative health data from Ontario, Canada. Adults who underwent bariatric surgery between 2010 and 2016 were matched 1:1 to controls on age, sex, body mass index (BMI), and diabetes status. The primary outcome was incident VTE (deep vein thrombosis or pulmonary embolism), measured after a 3-month landmark period. Hazard ratios (HRs) were estimated using Cox models adjusted for confounders, including time-varying VTE risk factors. We included 13 502 patients who underwent bariatric surgery and 13 502 matched controls. The mean age was 45.0 years (SD 11.1), and 81.4% were women. Median follow-up was 8.4 years. VTE incidence was 0.24 per 100 person-years in the surgical group and 0.26 in the control group. Bariatric surgery was associated with a 21% reduced risk of VTE (HR 0.79; 95% CI 0.66-0.96). Risk reduction was more pronounced in men (HR 0.59; 95% CI 0.36-0.96) and in patients with BMI < 50 kg/m². No benefit was observed in patients with BMI ≥ 50 kg/m² or those who had sleeve gastrectomy. Bariatric surgery is associated with a long-term reduction in VTE risk, particularly among men and individuals with moderate obesity. These findings support the reversibility of obesity-related thrombosis risk and inform long-term VTE prevention strategies.