Diabetes and endometrial cancer in the Iowa women's health study

Diabetes has been associated with increased risk of endometrial cancer in s ome epidemiological studies. Body mass index (BMI) and other measures of ob esity have been associated positively with both diabetes and endometrial ca ncer. It is not clear whether or not the association of diabetes with endom etrial cancer is explained entirely by obesity. Thus, we sought to test the hypothesis that diabetes is mot associated with endometrial cancer indepen dent of obesity, We examined the association between self-reported diabetes (onset at > 30 years of age) and incident endometrial cancer in a prospect ive cohort study of 24,664 postmenopausal women in Iowa. Over 12 years of f ollow-up, 346 cases occurred among the cohort at risk. Data were analyzed u sing proportional hazards regression models. Diabetes was analyzed as repor ted at baseline and as a time-dependent variable using information obtained during follow-up. After adjustment for BMI, waist:hip ratio, and other cov ariates, the relative risk (RR) for women with diabetes versus women withou t diabetes was 1.43 [95% confidence interval (CI), 0.98-2.1]. The diabetes association was confined to women in the upper two BMI quintiles (RR, 1.47; 95% CI, 0.98-2.20), but a formal test of interaction was not statistically significant. Analyses that included diabetes ascertained at baseline and a t follow-up gave similar results; the diabetes-associated RR in the higher BMI strata was 1.64 (95% CI, 1.16-2.31). We conclude that after adjustment for other risk factors, diabetes is associated with a modestly increased ri sk for endometrial cancer among women in this cohort.