Adolescent and adult soy intake and risk of breast cancer in Asian-Americans

Abstract

The association between soyfood intake and breast cancer risk is controversial. Most of the epidemiologic studies published on this topic in the 1990s were not designed to specifically address this question. We conducted a population-based, case-control study of breast cancer among Chinese, Japanese and Filipino women in Los Angeles County to further investigate the role of soy. Our primary objective was to quantify breast cancer risks associated with intake of soy during adolescence and adult life among Asian-American women. During 1995-1998, we successfully interviewed 501 breast cancer patients and 594 control subjects. Intake of soy among Asian-Americans is still relatively high; the median intake was 12 mg isoflavones/day, approximately one-third of that reported in a recent study in Shanghai, China. The risk of breast cancer was significantly inversely associated with soy intake during adolescence and adult life. After adjusting for age, specific Asian ethnicity, education, migration history and menstrual and reproductive factors, women who reported soy intake at least once per week during adolescence showed a statistically significantly reduced risk of breast cancer. There was also a significant trend of decreasing risk with increasing soy intake during adult life. When we considered soy intake during both adolescence and adult life, subjects who were high-soy consumers during both time periods showed the lowest risk (OR=0.53, 95% CI=0.36-0.78) compared with those who were low consumers during both time periods. Risk of breast cancer was intermediate among subjects who were high-soy consumers during adolescence and low-soy consumers during adult life (OR=0.77, 95% CI=0.51-1.10). Based on a relatively small number of subjects, the risk did not appear to differ between those who were low consumers during adolescence and high consumers during adult life. Results remained similar after adjustment for other potential confounders including other dietary and non-dietary risk factors for breast cancer. These results show that high soy intake in childhood in Asian-Americans is associated with reduced breast cancer risk. Risk may be further reduced by intake as an adult.

Inhibition of cell proliferation, induction of apoptosis, reactivation of DLC1, and modulation of other gene expression by dietary flavone in breast cancer cell lines

“…Among such external factors, diet is thought to play an important role. A low incidence of breast cancer in Asia has been attributed in part to a high intake of flavonoids [22,23]. The incidence of cancer increases when Asian women move to the United States, where the average diet is rich in fat and confers a strong significant protective effect during adolescence.…”

Green tea and risk of breast cancer in Asian Americans

“…Age at first pregnancy was not included in the baseline model since there was no significant improvement in the fit of the regression model with this variable. We considered additional lifestyle factors, including smoking habits; intake of alcohol, coffee, soy and dark leafy greens; family history of cancer; and physical activity, as they were found to be associated with tea consumption in this study (Table I) and in some previous studies or emerged as significant risk factors in this population 12,16 (referred as model B adjusted ORs in Table II 12,16 cases and controls were similar in terms of birthplace, education, age at menarche and body size but cases were significantly more likely to be nulliparous, had fewer live births, had lower consumption of soy and were less physically active than controls (data not shown). Table I shows the age-adjusted mean daily intake of black and green tea separately and the 2 teas combined by demographic and various lifestyle factors.…”

Urinary isoflavone excretion as a compliance measure in a soy intervention among young girls: a pilot study

“…According to experimental (Lamartiniere et al, 1995;Murrill et al, 1996;Hilakivi-Clarke et al, 1999) and epidemiological studies (Shu et al, 2001;Wu et al, 2002), the timing of soy exposure during developmental years may be crucial for the protective effects from soy. In animals, prepubertal exposure to soy appears to be more effective than adult exposure in reducing mammary tumor formation (Lamartiniere et al, 2002).…”

“…In animals, prepubertal exposure to soy appears to be more effective than adult exposure in reducing mammary tumor formation (Lamartiniere et al, 2002). Furthermore, two case-control studies revealed that women with high soy intake during adolescence had half the risk of breast cancer as compared to those who consumed fewer soy foods (Shu et al, 2001;Wu et al, 2002). Thus, regular soy consumption during childhood and adolescence may lower the risk for breast cancer later in life.…”