Adolescent meat intake and breast cancer risk

The breast is particularly vulnerable to carcinogenic influences during adolescence due to rapid proliferation of mammary cells and lack of terminal differentiation. We investigated consumption of adolescent red meat and other protein sources in relation to breast cancer risk in the Nurses’ Health Study II cohort. We followed prospectively 44,231 women aged 33–52 years who, in 1998, completed a detailed questionnaire about diet during adolescence. Relative risks (RR) and 95% confidence intervals (95%CI) were estimated using Cox proportional hazard regression. We documented 1132 breast cancer cases during 13-year follow-up. In multivariable Cox regression models with major breast cancer risk factors adjustment, greater consumption of total red meat in adolescence was significantly associated with higher premenopausal breast cancer risk (highest vs. lowest quintiles, RR, 1.43; 95%CI, 1.05–1.94; Ptrend 50.007), but not postmenopausal breast cancer. Adolescent intake of poultry was associated with lower risk of breast cancer overall (RR, 0.76; 95%CI, 0.60–0.97; for each serving/day). Adolescent intakes of iron, heme iron, fish, eggs, legumes and nuts were not associated with breast cancer. Replacement of one serving/day of total red meat with one serving of combination of poultry, fish, legumes, and nuts was associated with a 15% lower risk of breast cancer overall (RR, 0.85; 95%CI, 0.74–0.96) and a 23% lower risk of premenopausal breast cancer (RR, 0.77; 95%CI, 0.64– 0.92). In conclusion, higher consumption of red meat during adolescence was associated with premenopausal breast cancer. Substituting other dietary protein sources for red meat in adolescent diet may decrease premenopausal breast cancer risk. The relation between intake of red meat and breast cancer has been examined in many studies; the overall evidence from a pooled analysis of cohort studies 1 and a recent meta-analysis 2 has not supported an important association. However, most of this evidence has been based on diet during midlife and later. In contrast, among women in Nurses’ Health Study II (NHSII) cohort, high intake of red meat in early adulthood was associated with increased breast cancer incidence. 3 Furthermore, vegetable protein consumption at age 14 was associated with lower risk of benign breast disease in early adulthood. 4 Therefore, one potential explanation for the overall lack of association in previous studies is the timing of dietary assessment. Mammary glands may be particularly vulnerable to breast carcinogenesis during childhood due to rapid proliferation of cells and lack of terminal differentiation. The evidence for this window of vulnerability was demonstrated in the atomic bombings of Hiroshima and Nagasaki and was also seen with radiation treatment for Hodgkin’s lymphoma; in both cases exposure to radiation in childhood and early adult life was associated with subsequent risk of breast cancer, whereas exposure after age 30 had little effect. 5–7 In an early analysis of the NHSII with 7 years follow-up and with 455 incident invasive breast cancer cases, 8 intake of total red meat (processed plus unprocessed) during adolescence was associated with an increased risk of premenopausal breast cancer. This updated analysis provided an examination of animal and vegetable sources of protein during adolescence including intakes of total red meat (unprocessed plus processed red meat), poultry, fish, eggs, legumes and nuts in relation to breast cancer incidence with almost triple the number of cases and twice the length of follow-up. In addition, we were able to examine breast cancers separately by menopausal status and estrogen receptor (ER) and progesterone receptor (PR) status.