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

ABSTRACT 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/m 2 . No benefit was observed in patients with BMI ≥ 50 kg/m 2 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.