Plasma carotenoids and risk of breast cancer over 20 y of follow-up.

BACKGROUND Increasing evidence suggests that carotenoids, which are micronutrients in fruit and vegetables, reduce breast cancer risk. Whether carotenoids are important early or late in carcinogenesis is unclear, and limited analyses have been conducted by breast tumor subtypes. OBJECTIVES We sought to examine issues of the timing of carotenoid exposure as well as associations by breast tumor subtypes. DESIGN We conducted a nested case-control study of plasma carotenoids measured by using reverse-phase high-performance liquid chromatography and breast cancer risk in the Nurses' Health Study. In 1989-1990, 32,826 women donated blood samples; in 2000-2002, 18,743 of these women contributed a second blood sample. Between the first blood collection and June 2010, 2188 breast cancer cases were diagnosed (579 cases were diagnosed after the second collection) and matched with control subjects. RRs and 95% CIs were calculated by using conditional logistic regression adjusted for several breast cancer risk factors. RESULTS Higher concentrations of α-carotene, β-carotene, lycopene, and total carotenoids were associated with 18-28% statistically significantly lower risks of breast cancer (e.g., β-carotene top compared with bottom quintile RR: 0.72; 95% CI: 0.59, 0.88; P-trend < 0.001). Associations were apparent for total carotenoids measured ≥10 y before diagnosis (top compared with bottom quintile RR: 0.69; 95% CI: 0.50, 0.95; P-trend = 0.01) as well as those <10 y before diagnosis (RR: 0.79; 95% CI: 0.64, 0.98; P-trend = 0.04, P-interaction = 0.11). Carotenoid concentrations were strongly inversely associated with breast cancer recurrence and death (e.g., β-carotene top compared with bottom quintile RR: 0.32; 95% CI: 0.21, 0.51; P-trend < 0.001) compared with not recurrent and not lethal disease (P-heterogeneity < 0.001). CONCLUSION In this large prospective analysis with 20 y of follow-up, women with high plasma carotenoids were at reduced breast cancer risk particularly for more aggressive and ultimately fatal disease.