Serum insulin and glucose levels and breast cancer incidence: the atherosclerosis risk in communities study.

The authors examined the association of breast cancer incidence with serum levels of insulin and glucose in a cohort of 7,894 women aged 45-64 years from four US communities. Anthropometric factors and fasting levels of insulin and glucose were measured at baseline (1987-1989). Over an average follow-up period of 7.1 years (1987-1995), 187 breast cancer cases were ascertained. Breast cancer was associated positively with body mass index but not with waist:hip ratio or serum insulin level. After adjustment for age, race, and study site, the incidence of breast cancer was 60% higher among diabetic women than among women with fasting glucose levels under 100 mg/dl, but this association was attenuated after further adjustment for body mass index and other covariates (adjusted rate ratio = 1.39, 95% confidence interval: 0.86, 2.23). Circulating insulin levels were not predictive of future breast cancer incidence, but there may be a weak association with type 2 diabetes, perhaps modulated via increased adiposity.