THE ASSOCIATION OF HEIGHT, WEIGHT, MENSTRUAL AND REPRODUCTIVE EVENTS WITH BREAST-CANCER - RESULTS FROM 2 PROSPECTIVE STUDIES ON THE ISLAND OF GUERNSEY (UNITED-KINGDOM)

The association with breast cancer of menstrual and reproductive event s, family history of breast cancer, and body size have been studied on two cohorts of 6,706 volunteers on the island of Guernsey (United Kin gdom), 168 of whom had breast cancer detected during follow-up. The me dian follow-up time of the non-cases was 21 years in the first study a nd 10 years in the second. A time-dependent Cox regression model was f itted to the data with age as the time-dependent variable in order to represent the effect of changing menopausal status. Other variables ex amined in the model were age at menarche, parity, age at first birth, family history of breast cancer, height, weight (both directly measure d), relative weight (weight [kg]/height[m]), and Quetelet's body mass index (weight[kg]/height[M]2). Interactions between age and all other covariates also were examined. Family history was found to be the most important risk factor for women aged less than 51 years (relative ris k [RR] = 3.5, 95 percent confidence interval [CI] = 2.0-6.0), and inte rvals between menarche and first birth longer than 14 years were found to increase significantly the risk of breast cancer in women older th an 61 years (RR = 2.4, CI = 1.3-4.4). Height was the only indicator of body size which was associated significantly with risk of breast canc er, the estimated regression coefficient indicating an increase in ris k of about 70 percent for women on the 90th centile of height relative to those on the 10th centile. A survey of the literature showed that the association between risk of breast cancer and height was found in those studies which used direct measurements of height but not in othe rs which used self-reported values.