Adolescent dietary patterns and premenopausal breast cancer incidence.

Mammary tissue experiences the highest rate of proliferation during adolescence representing a period of heightened susceptibility. Few prospective studies have examined adolescent diet and breast cancer, and none have examined dietary patterns. Thus, we examined the association between adolescent dietary patterns and a diet quality index, the Alternative Healthy Eating Index (AHEI), and breast cancer in the Nurses' Health Study II among those who completed a 124-item food frequency questionnaire about their high-school diet (HS-FFQ). Cox proportional hazards regression models were used to calculate hazard ratios (HR) and 95% confidence intervals (95% CI). Among 45204 women who completed the HS-FFQ, 863 cases of premenopausal breast cancer and 614 cases of postmenopausal cancer were diagnosed. A marginal inverse association was observed between the 'prudent' dietary pattern, characterized by high intake of vegetables, fruits, legumes, fish and poultry, and premenopausal breast cancer. Women in fifth quintile had a multivariable adjusted HR (95% CI) of 0.84 (0.67-1.04) for premenopausal breast cancer (P trend = 0.07) compared with the first quintile. Scoring higher on the AHEI was borderline significantly associated with premenopausal breast cancer with a HR of 0.81 (0.64-1.01) for the fifth quintile (P trend = 0.08), and this association appeared to be stronger for estrogen receptor-negative/progesterone receptor-negative tumors. No association was observed between the 'Western' pattern or the 'fast-food' pattern. Results were similar for each of these patterns when both premenopausal and postmenopausal breast cancer were considered together. An overall healthy diet during adolescence, similar to the prudent dietary pattern or adherence to the AHEI, may contribute to reducing the risk of breast cancer.