DOES BODY-FAT DISTRIBUTION PROMOTE FAMILIAL AGGREGATION OF ADULT-ONSET DIABETES-MELLITUS AND POSTMENOPAUSAL BREAST-CANCER

Noninsulin dependent diabetes mellitus and postmenopausal breast cance r share a number of risk factors, including obesity, increased waist-t o-hip ratio, and a positive family history. If risk for these diseases is mediated through a familial tendency for abdominal obesity, then o ne might expect to see familial clustering of both diseases. We analyz ed data from a prospective cohort study of 41,837 Iowa women age 55-69 years. Diabetes was not associated with incidence of breast cancer [r elative risk (RR) = 0.97]. The association between family history of b reast cancer and breast cancer incidence, however, was slightly modifi ed by individual history of diabetes: a positive family history of bre ast cancer in the absence of baseline diabetes was associated with a r elative risk of 1.36 [95% confidence interval (CI) = 1.08-1.70], where as the presence of both factors was associated with a RR of 1.87 (95% CI = 0.93-3.76). Adjustment for waist-to-hip ratio greatly diminished this difference. Conversely, a family history of breast cancer was ass ociated with a RR of 5-year diabetes mortality of 1.94 (95% CI = 1.17- 3.24) that persisted after stratification by tertile of waist to-hip r atio. No clear association of family history of breast cancer and wais t-to-hip ratio for self-reported diabetes incidence was evident. These data are indicative of a complex interrelation between waist-to-hip r atio, familial predisposition, diabetes, and breast cancer.