Background: Excessive body weight is known to increase the risk of postmenopausal, but not premenopausal breast cancer. Some studies have suggested that being overweight is protective against premenopausal breast cancer, but the evidence is not compelling. Much less is known about the role of body fat distribution in either pre- or postmenopausal breast cancer.
Methods: Breast cancer risk was examined in relation to body weight, height, Quetelet index (kg/m2), and waist/hip ratio (WHR) in the New York University Women's Health Study, a prospective cohort study. Cases were 109 premenopausal and 150 postmenopausal women diagnosed with breast cancer between 1985 and 1994. Non-cases were 8,157 cohort members free of breast cancer.
Results: Among premenopausal women, there was an increasing risk of breast cancer with increasing WHR. The relative risk (RR) of breast cancer increased to 1.72 (95% confidence interval [CI]: 1.0-3.1) in the upper quartile of WHR. The association was limited to subjects who had elevated Quetelet index, but not among those with lower weight. Overall, Quetelet index itself was not related to breast cancer risk in the premenopausal group, but there was a protective association among those ranking below the median WHR. In postmenopausal women, the RR for breast cancer increased to 2.36 (95% CI: 1.4-3.9) in the upper quartile of Quetelet index, but there was no association with WHR. Height was not associated with breast cancer in this study.
Conclusions: The study confirms that excessive body weight increases breast cancer risk in postmenopausal women. On the contrary, in premenopausal women, excessive body weight may be protective among women who have a lower-body type of fat accumulation (low WHR). An upper-body fat accumulation (high WHR) is a predictor of breast cancer risk in premenopausal women, and this effect is especially pronounced among subjects who are overweight.