Background: The chemopreventive activities of cruciferous vegetables were recognized in the early 1990s, followed by a growth of evidence in various cancer models, including breast cancer. To our knowledge, no studies have examined whether consumption of cruciferous vegetables has changed accordingly, and what impact, if any, on breast cancer risk may have resulted. Objective: The time trend in cruciferous vegetable intake was investigated between 1982 and 1998, and its associations with breast cancer risk were examined. Methods: In a hospital-based case-control study in 1491 patients with breast cancer and 1482 controls, loess curves were constructed to describe the relation between median consumption of cruciferous vegetables and year of admission. ORs and 95% CIs were calculated with unconditional logistic regression, adjusting for age, year of admission, family income, body mass index, cigarette smoking, age at menarche, parity, age at first birth, family history of breast cancer, hormone replacement therapy, and total meat intake. Results: Consumption patterns differed between cases and controls. A slow but steady increase in cruciferous vegetable intake was observed in the cases, although among controls, cruciferous vegetable consumption increased from 1982 to 1987, reached a plateau during 1988-1992, and then declined from 1993 to 1998. Accordingly, although an overall inverse association with breast cancer risk was observed for cruciferous vegetable intake (highest compared with lowest quartile-OR: 0.68; 95% CI: 0.55, 0.86; P-trend = 0.0006), the inverse association tended to be more pronounced within more recent-year strata, with an OR of 0.52 (95% CI: 0.33, 0.83) for 1993-1998 compared with an OR of 0.89 (95% CI: 0.64, 1.23) for 1982-1987. Conclusions: The consumption of cruciferous vegetables increased during the past 2 decades, showing different trends in cases and controls. The subtle but sustained increase in cruciferous vegetable intake reported by the cases could influence association studies with breast cancer risk.
Keywords: breast cancer; case-control study; cruciferous vegetable; risk association; self-reported consumption.