Body size across the life course, mammographic density, and risk of breast cancer

Abstract

Adult body mass index (BMI) is inversely associated with premenopausal breast cancer risk, and childhood and adolescent body size is inversely associated with breast cancer risk in pre- and postmenopausal women. Breast density is inversely related to body size and may play a role in the association of body size with breast cancer risk. The authors conducted a nested case-control study including 1,528 cases and 2,844 controls from the Nurses' Health Study (1989-2004) and Nurses' Health Study II (1996-2003). Prior to breast cancer diagnosis, participants reported their body fatness during childhood and adolescence, BMI at age 18 years, and current BMI. Mammographic density was measured by using a computer-assisted thresholding method. The inverse association between adult BMI and premenopausal breast cancer (for BMI ≥30 vs. BMI 20-22.4, odds ratio = 0.64, 95% confidence interval: 0.38, 1.06) (P(trend) = 0.36) became positive after adjustment for mammographic density (odds ratio = 1.28, 95% confidence interval: 0.72, 2.30) (P(trend) = 0.07). Conversely, the inverse association between childhood and adolescent body size and breast cancer risk remained after adjustment for mammographic density. The inverse association between adult BMI and premenopausal breast cancer risk may be partially due to negative confounding by mammographic density. Conversely, mammographic density does not appear to explain the inverse association between childhood and adolescent body fatness and breast cancer risk.

Figure 1.

Description of mammogram collection in the Nurses’ Health Study (NHS, 1989–2004) and the Nurses’ Health Study II (NHS II, 1996–2003).

Figure 2.

The 9-figure body size scale used to assess body fatness at ages 5, 10, and 20 years in the Nurses’ Health Study (1988) and the Nurses’ Health Study II (1989). Reprinted from Genetics of Neurological and Psychiatric Disorders by S. S. Kety et al., eds. (40). Copyright 1983, with permission from Wolters Kluwer.