Impact of Changes in Obesity and Abdominal Obesity on Endometrial Cancer Risk in Young Korean Women: A Nationwide Cohort Study

Abstract Background: The increasing incidence of endometrial cancer in young women parallels the increasing prevalence of obesity, a well-established risk factor. However, the impact of longitudinal changes in obesity and abdominal obesity on early-onset endometrial cancer remains insufficiently understood. Methods: This nationwide cohort study utilized data from the Korean National Health Insurance Service. Women, ages 20 to 39 years, who underwent two health examinations at a 3-year interval between 2009 and 2015, with no history of cancer, were included. Participants were categorized based on changes in obesity (body mass index ≥25 kg/m2) or abdominal obesity (waist circumference ≥85 cm) into four groups: stable non-obese, non-obese to obese, obese to non-obese, and stable obese. The risk of endometrial cancer was assessed using Cox proportional hazards models. Results: Among 935,600 women, 798 developed endometrial cancer. Compared with the stable non-obese group, adjusted HRs for endometrial cancer were 1.940 (1.468–2.563), 2.083 (1.447–3.001), and 2.083 (1.447–3.001) in the non-obese to obese, obese to non-obese, and stable obese groups, respectively. With regard to abdominal obesity, the adjusted HRs were 2.048 (1.581–2.651), 2.302 (1.684–3.146), and 4.394 (3.557–5.427), respectively. The risk of cancer was higher in the obese to non-obese group than in the non-obese to obese group. Conclusions: Changes in obesity and abdominal obesity statuses were associated with early-onset endometrial cancer, with persistent abdominal obesity showing the highest risk. Impact: These findings support the need for early, sustained obesity interventions to reduce endometrial cancer risk in young women.