Dietary isoflavone intake and breast cancer risk in case–control studies in Japanese, Japanese Brazilians, and non-Japanese Brazilians

Abstract

Although epidemiologic studies have shown an inverse association between isoflavones and breast cancer risk, little evidence for a dose-response relation is available. We conducted hospital-based case-control studies of patients aged 20-74 years with primary, incident, histologically confirmed invasive breast cancer, and matched controls from medical checkup examinees in Nagano, Japan and from cancer-free patients in São Paulo, Brazil. A total of 850 pairs (390 Japanese, 81 Japanese Brazilians and 379 non-Japanese Brazilians) completed validated food frequency questionnaires. The odds ratio of breast cancer according to isoflavone intake was estimated using a conditional logistic regression model. We found a statistically significant inverse association between isoflavone intake and the risk of breast cancer for Japanese Brazilians and non-Japanese Brazilians. For Japanese, a non-significant inverse association was limited to postmenopausal women. In the three populations combined, breast cancer risk linearly decreased from 'no' to 'moderate' isoflavone intake and thereafter leveled off. Compared to non-consumers, adjusted odds ratios (95% confidence interval) for consumers in increasing quintile intake categories (median intake in each category: 8.7, 23.1, 33.8, 45.7, and 71.3 mg/day) were 0.69 (0.44-1.09), 0.54 (0.31-0.94), 0.45 (0.26-0.77), 0.34 (0.19-0.62), and 0.43 (0.24-0.76), respectively. Overall, we found an inverse association between dietary isoflavone intake and risk of breast cancer. Our finding suggests a risk-reducing rather than risk-enhancing effect of isoflavones on breast cancer within the range achievable from dietary intake alone. In addition, women may benefit from risk reduction if they consume at least moderate amounts of isoflavones.

Serum organochlorines and breast cancer risk in Japanese women: a case–control study

“…A second noted a higher range of mirex exposure (mean 0.037 ng/g serum among controls [52]) than that seen here, likely because of the history of use of this agent in the US versus no use in Japan [53]. Furthermore, Asian women have lower sex hormone levels [48] and higher dietary intake of phytoestrogens [54,55] than Caucasian women in Western countries. These differences may partly explain why these previous results were not reproduced here.…”

Fragment c gamma receptor gene polymorphisms and breast cancer risk in case–control studies in Japanese, Japanese Brazilians, and non-Japanese Brazilians

“…Characteristics of case patients and control subjects have been described elsewhere [18,19]. For Japanese, the proportion of premenopausal women, current smokers, and vitamin supplement users was higher in cases than in controls; and cases tended to have a family history of breast cancer and history of benign breast disease.…”

“…In addition to determining lifestyle factors and genetic susceptibility to the risk of breast cancer, the protocols of these studies were also designed to compare potential risk factors among Japanese living in Nagano, Japan, and Japanese Brazilians and non-Japanese Brazilians living in São Paulo, Brazil [18,19]. Eligible case patients were a consecutive series of female patients aged 20-74 years with newly diagnosed and histologically confirmed invasive breast cancer.…”

Genetic polymorphisms in estrogen metabolism and breast cancer risk in case–control studies in Japanese, Japanese Brazilians and non-Japanese Brazilians

“…26 Eligible cases were a consecutive series of female patients aged 20-74 years with newly diagnosed and histologically confirmed invasive breast cancer. Cases were recruited between 2001 and 2005 at four hospitals in Nagano, and between 2001 and 2006 at eight hospitals in São Paulo.…”