Epidemiology of soy exposures and breast cancer risk

Soy food intake and breast cancer survival

CONTEXT

Soy foods are rich in isoflavones, a major group of phytoestrogens that have been hypothesized to reduce the risk of breast cancer. However, the estrogen-like effect of isoflavones and the potential interaction between isoflavones and tamoxifen have led to concern about soy food consumption among breast cancer patients.

OBJECTIVE

To evaluate the association of soy food intake after diagnosis of breast cancer with total mortality and cancer recurrence.

DESIGN, SETTING, AND PARTICIPANTS

The Shanghai Breast Cancer Survival Study, a large, population-based cohort study of 5042 female breast cancer survivors in China. Women aged 20 to 75 years with diagnoses between March 2002 and April 2006 were recruited and followed up through June 2009. Information on cancer diagnosis and treatment, lifestyle exposures after cancer diagnosis, and disease progression was collected at approximately 6 months after cancer diagnosis and was reassessed at 3 follow-up interviews conducted at 18, 36, and 60 months after diagnosis. Annual record linkage with the Shanghai Vital Statistics Registry database was carried out to obtain survival information for participants who were lost to follow-up. Medical charts were reviewed to verify disease and treatment information.

MAIN OUTCOME MEASURES

Total mortality and breast cancer recurrence or breast cancer-related deaths. Cox regression analysis was carried out with adjustment for known clinical predictors and other lifestyle factors. Soy food intake was treated as a time-dependent variable.

RESULTS

During the median follow-up of 3.9 years (range, 0.5-6.2 years), 444 deaths and 534 recurrences or breast cancer-related deaths were documented in 5033 surgically treated breast cancer patients. Soy food intake, as measured by either soy protein or soy isoflavone intake, was inversely associated with mortality and recurrence. The hazard ratio associated with the highest quartile of soy protein intake was 0.71 (95% confidence interval [CI], 0.54-0.92) for total mortality and 0.68 (95% CI, 0.54-0.87) for recurrence compared with the lowest quartile of intake. The multivariate-adjusted 4-year mortality rates were 10.3% and 7.4%, and the 4-year recurrence rates were 11.2% and 8.0%, respectively, for women in the lowest and highest quartiles of soy protein intake. The inverse association was evident among women with either estrogen receptor-positive or -negative breast cancer and was present in both users and nonusers of tamoxifen.

CONCLUSION

Among women with breast cancer, soy food consumption was significantly associated with decreased risk of death and recurrence.

Flavonoids from the heartwood of the Thai medicinal plant Dalbergia parviflora and their effects on estrogenic-responsive human breast cancer cells

From the heartwood of Dalbergia parviflora, eight new compounds, khrinones A (1), B (2), C (3), D (4), and E (5), isodarparvinol B (6), dalparvin (7), and (3S)-sativanone (22), along with 32 known compounds, have been isolated and characterized as 17 isoflavones, nine isoflavanones, five flavanones, six isoflavans, and three miscellaneous substances. Isolates were evaluated for their cell proliferation stimulatory activity against the MCF-7 and T47D human breast cancer cell lines, and their luciferase inductive effects using luciferase transiently transfected MCF-7/luc and T47D/luc cells were also determined. Isoflavones such as genistein (10), biochanin A (11), tectorigenin (12), and 2'-methoxyformononetin (13) stimulated the proliferation of both cells, and concentrations of lower than 1 muM of these compounds showed equivalent activity to 10 pM of estradiol (E2). The new isoflavanone (22) also showed activity against both cell types, although it was weaker than that of the corresponding isoflavone (2'-methoxyformononetin, 13). Two optically active isoflavanones (22 and 24: (3S)-violanone) stimulated the proliferation of both cell lines at lower concentrations than three racemates (21: vestitone, 23: 7,3'-dihydroxy-4'-methoxyisoflavanone, and 25: 3-O-methylviolanone). Bowdichione (20), an isoflavone with a quinone structure in its B-ring, showed activity against only one cell line associated with MCF-7 in these assays.

A novel look into estrogen receptor-negative breast cancer prevention with the natural, multifunctional signal transduction inhibitor deguelin

This perspective on Murillo et al. (beginning on page 942 in this issue of the journal) examines the potential of the naturally derived agent deguelin to prevent mammary tumorigenesis. These investigators showed that deguelin inhibits wnt/beta-catenin signaling in breast cancer cell lines, in addition to inhibiting other previously reported signaling pathways. Our growing understanding of deguelin mechanisms could lead to important advances in the prevention of estrogen receptor-negative breast and other cancers.

The use of herbal preparations to alleviate climacteric disorders and risk of postmenopausal breast cancer in a German case-control study

BACKGROUND

The use of herbal preparations (HEP) to alleviate climacteric disorders is expected to increase as women seek alternatives to menopausal hormone therapy to avoid the associated breast cancer risk. Data are sparse on the long-term effects of HEP containing phytoestrogens and black cohosh on breast cancer risk.

METHODS

Within a German case-control study, associations between patterns of HEP use and incident breast cancer were investigated in 10,121 postmenopausal women (3,464 cases, 6,657 controls). Information on HEP use was collected in face-to-face interviews supported by a list of brand names. Multivariate logistic and polytomous regression analyses were done.

FINDINGS

Ever use of HEP (9.9%) was inversely associated with invasive breast cancer [odds ratio (OR), 0.74; 95% confidence interval (CI), 0.63-0.87] in a dose-dependent manner (OR, 0.96 per year of use; P = 0.03). Classes of HEP did not differ significantly (P(heterogeneity) = 0.81). Risks for invasive ductal (OR, 0.72; 95% CI, 0.60-0.87) and combined lobular/mixed/tubular tumors (OR, 0.76; 95% CI, 0.58-1.01) were similarly reduced by any HEP use but not for in situ carcinomas (1.34; 95% CI, 0.86-2.09). There were no substantial differences in associations of HEP use by estrogen receptor status (ER(+) OR, 0.74; 95% CI, 0.62-0.89; ER- OR, 0.68, 95% CI, 0.50-0.93) and progesterone receptor status of the tumor.

INTERPRETATION

Our findings support the hypothesis that HEP use protects from invasive breast cancer in postmenopausal women. Among conceivable modes of action, those independent of estrogen receptor-mediated pathways seem to be involved (i.e., cytotoxicity, apoptosis).

Urinary phytoestrogen excretion and postmenopausal breast cancer risk: the multiethnic cohort study

The objective of this study was to examine the association of urinary phytoestrogens with the risk of postmenopausal breast cancer. Participants in the Multiethnic Cohort Study included 36,458 postmenopausal women who provided blood or urine specimens. A nested case-control study of breast cancer with biospecimens was created in which cases diagnosed after specimen collection were matched to two controls. Two hundred fifty-one women with breast cancer and 462 controls had urine available for analysis of urinary phytoestrogens. Odds ratios (OR) and 95% confidence intervals (CI) were obtained using conditional logistic regression. A nonmonotonic inverse trend (P = 0.04) in breast cancer risk was associated with increasing urinary excretion of genistein (OR 25th-75th percentile, 0.88; 95% CI, 0.78-0.99) and total isoflavones (OR 25th-75th percentile, 0.80; 95% CI, 0.65-0.99). A significant reduction in breast cancer risk in Japanese-American women was associated with the highest compared with the lowest quartile excretion of urinary daidzein (OR, 0.41; 95% CI, 0.19-0.89; P(trend), 0.005). The risk of breast cancer was reduced among White women with the highest compared with the lowest quartile excretion of equol (OR, 0.27; 95% CI, 0.08-0.95), although the trend in risk was not significant (P = 0.07). Our results provide some support to the hypothesis that a diet rich in isoflavones from soy products reduces the risk of postmenopausal breast cancer, particularly in populations with comparatively high excretion of phytoestrogens.

Soy intake is associated with increased 2-hydroxylation and decreased 16alpha-hydroxylation of estrogens in Asian-American women

INTRODUCTION

In Asian and Asian-American women, soy consumption is associated with reduced breast cancer risk, perhaps due to its effects on estrogen production or metabolism. In a sample of Asian-American women, we investigated the associations of usual adult soy intake with the urinary concentrations of 15 estrogens and estrogen metabolites (EM) measured using liquid chromatography-tandem mass spectrometry.

METHODS

Participants included 430 Chinese-American, Japanese-American, and Filipino-American women, ages 20 to 55 years, and living in San Francisco-Oakland (California), Los Angeles (California), or Oahu (Hawaii). They were postmenopausal (n = 167) or premenopausal in luteal phase (n = 263) when 12-hour urine samples were collected. Robust linear regression was used to assess soy tertiles as predictors of log-transformed EM measures. Individual and grouped EM were considered as concentrations (pmol/mg creatinine) and as percentages of total EM (%EM).

RESULTS

Factor analysis confirmed that EM groups defined by metabolic pathways appropriately captured covariation in EM profiles. Total EM concentrations were not significantly associated with soy in premenopausal or postmenopausal women. Among all women, %2-hydroxylated EM and %4-hydroxylation pathway EM were 16% higher (P(trend) = 0.02) and 19% higher (P(trend) = 0.03) in the highest versus lowest soy tertiles, respectively. In contrast, 16% hydroxylated EM were 11% lower (P(trend) < 0.01). Results were consistent across ethnic and menopausal groups and after adjustment for westernization measured by birthplace (Asia or United States).

DISCUSSION

Findings suggest that regular soy intake is associated with increased ratios of 2:16-pathway EM and with higher relative levels of 4-hydroxylated EM. The observed variations in estrogen metabolism might modify breast cancer risk.

Position of the American Dietetic Association: vegetarian diets

It is the position of the American Dietetic Association that appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases. Well-planned vegetarian diets are appropriate for individuals during all stages of the life cycle, including pregnancy, lactation, infancy, childhood, and adolescence, and for athletes. A vegetarian diet is defined as one that does not include meat (including fowl) or seafood, or products containing those foods. This article reviews the current data related to key nutrients for vegetarians including protein, n-3 fatty acids, iron, zinc, iodine, calcium, and vitamins D and B-12. A vegetarian diet can meet current recommendations for all of these nutrients. In some cases, supplements or fortified foods can provide useful amounts of important nutrients. An evidence- based review showed that vegetarian diets can be nutritionally adequate in pregnancy and result in positive maternal and infant health outcomes. The results of an evidence-based review showed that a vegetarian diet is associated with a lower risk of death from ischemic heart disease. Vegetarians also appear to have lower low-density lipoprotein cholesterol levels, lower blood pressure, and lower rates of hypertension and type 2 diabetes than nonvegetarians. Furthermore, vegetarians tend to have a lower body mass index and lower overall cancer rates. Features of a vegetarian diet that may reduce risk of chronic disease include lower intakes of saturated fat and cholesterol and higher intakes of fruits, vegetables, whole grains, nuts, soy products, fiber, and phytochemicals. The variability of dietary practices among vegetarians makes individual assessment of dietary adequacy essential. In addition to assessing dietary adequacy, food and nutrition professionals can also play key roles in educating vegetarians about sources of specific nutrients, food purchase and preparation, and dietary modifications to meet their needs.

Impact of diet on breast cancer risk

PURPOSE OF REVIEW

Breast cancer is the most common female cancer in Western Europe and North America, and becoming an increasing problem in developing countries such as India and China. We review recent studies (published 1 January 2007-31 August 2008) on the impact of diet on breast cancer risk.

RECENT FINDINGS

Recent studies have focused on the controversial association for dietary fat and breast cancer as well as the role of newer aspects such as glycemic index, dietary patterns and diet-gene interactions. Evidence that some of the associations may be modified by oestrogen and progesterone receptor status has been presented. Still, only alcohol intake, being overweight and weight gain have shown consistent and strong positive associations with breast cancer risk. The reasons for the null or weak associations often observed regarding diet and breast cancer might be several. For example, there may be no causal association, or existing associations may be masked by measurement error, timing of dietary exposure and differences according to tumour characteristics or diet-gene interactions.

SUMMARY

Numerous epidemiological studies on diet and breast cancer have been published during our review period. Still, only alcohol intake, being overweight and weight gain have shown consistent and strong positive associations with breast cancer risk.

Adolescent and adult soy food intake and breast cancer risk: results from the Shanghai Women's Health Study

BACKGROUND

Soy food is a rich source of isoflavones--a class of phytoestrogens that has both antiestrogenic and anticarcinogenic properties.

OBJECTIVE

The objective was to evaluate the association of adolescent and adult soy food intake with breast cancer risk in a cohort of 73,223 Chinese women who participated in the Shanghai Women's Health Study.

DESIGN

A validated food-frequency questionnaire was used to assess usual dietary intake during adulthood and adolescence. After a mean follow-up of 7.4 y, 592 incident cases of breast cancer were identified for longitudinal analyses by using Cox regressions.

RESULTS

Adult soy food consumption, measured either by soy protein or isoflavone intake, was inversely associated with the risk of premenopausal breast cancer, and the association was highly statistically significant (P for trend < 0.001). The multivariate-adjusted relative risks (RRs) for the upper intake quintile compared with the lowest quintile were 0.41 (95% CI: 0.25, 0.70) for soy protein intake and 0.44 (95% CI: 0.26, 0.73) for isoflavone intake. High intake of soy foods during adolescence was also associated with a reduced risk of premenopausal breast cancer (RR: 0.57; 95% CI: 0.34, 0.97). Women who consumed a high amount of soy foods consistently during adolescence and adulthood had a substantially reduced risk of breast cancer. No significant association with soy food consumption was found for postmenopausal breast cancer.

CONCLUSION

This large, population-based, prospective cohort study provides strong evidence of a protective effect of soy food intake against premenopausal breast cancer.

Lignans and breast cancer risk in pre- and post-menopausal women: meta-analyses of observational studies

Phyto-oestrogens are plant compounds structurally similar to oestradiol, which have been proposed to have protective effects against breast cancer. The main class of phyto-oestrogens in the Western diet is lignans. Literature reports on the effect of lignans in breast cancer risk have been conflicting. We performed three separate meta-analyses to examine the relationships between (i) plant lignan intake, (ii) enterolignan exposure and (iii) blood enterolactone levels and breast cancer risk. Medline, BIOSIS and EMBASE databases were searched for publications up to 30 September 2008, and 23 studies were included in the random effects meta-analyses. Overall, there was little association between high plant lignan intake and breast cancer risk (11 studies, combined odds ratio (OR): 0.93, 95% confidence interval (95% CI): 0.83-1.03, P=0.15), but this association was subjected to marked heterogeneity (I(2)=44%). Restricting the analysis to post-menopausal women, high levels of plant lignan intake were associated with reduced breast cancer risk (7 studies, combined OR: 0.85, 95% CI: 0.78, 0.93, P<0.001) and heterogeneity was markedly reduced (I(2)=0%). High enterolignan exposure was also associated with breast cancer (5 studies, combined OR: 0.73, 95% CI: 0.57, 0.92, P=0.009) but, again, there was marked heterogeneity (I(2)=63%). No association was found with blood enterolactone levels (combined OR: 0.82, 95% CI: 0.59-1.14, P=0.24). In conclusion, plant lignans may be associated with a small reduction in post-menopausal breast cancer risk, but further studies are required to confirm these results.

Various doses of soy isoflavones do not modify mammographic density in postmenopausal women

Soy isoflavones have functional similarity to human estrogens and may protect against breast cancer as a result of their antiestrogenic activity or increase risk as a result of their estrogen-like properties. We examined the relation between isoflavone supplementation and mammographic density, a strong marker for breast cancer risk, among postmenopausal women. The Osteoporosis Prevention Using Soy (OPUS) study, a multi-site, randomized, double-blinded, and placebo-controlled trial assigned 406 postmenopausal women to 80 or 120 mg/d of isoflavones each or a placebo for 2 y. Percent densities were assessed in digitized mammograms using a computer-assisted method. The mammogram reader did not know the treatment status and the time of mammograms. We applied mixed models to compare breast density by treatment while considering the repeated measures. The mammographic density analysis included 358 women, 88.2% of the OPUS participants; 303 had a complete set of 3 mammograms, 49 had 2, and 6 had only 1 mammogram. At baseline, the groups were similar in age, BMI, and percent density, but mean breast density differed by study site (P = 0.02). A model with all mammograms did not show a treatment effect on any mammographic measure, but the change over time was significant; breast density decreased by 1.6%/y across groups (P < 0.001). Stratification by age and BMI did not reveal any effects in subgroups. In this randomized 2-y trial, isoflavone supplements did not modify breast density in postmenopausal women. These findings offer reassurance that isoflavones do not act like hormone replacement medication on breast density.

Isoflavone, polymorphisms in estrogen receptor genes and breast cancer risk in case-control studies in Japanese, Japanese Brazilians and non-Japanese Brazilians

Epidemiologic studies have shown an inverse association between isoflavones and breast cancer risk. Because isoflavones bind estrogen receptors, we hypothesized that polymorphisms in the estrogen receptor genes might modify the association between isoflavone intake and breast cancer risk. 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 among medical checkup examinees in Nagano, Japan, and from cancer-free patients in São Paulo, Brazil. A total of 846 pairs (388 Japanese, 79 Japanese Brazilians and 379 non-Japanese Brazilians) completed validated food frequency questionnaires, and provided blood samples. Five single nucleotide polymorphisms in the estrogen receptor alpha (rs9340799, rs1913474, and rs2234693) and beta (rs4986938 and rs1256049) genes were genotyped. We found no consistent association between the five single nucleotide polymorphisms and breast cancer risk among the three populations. In analyses of combinations of isoflavone intake and single nucleotide polymorphisms, an inverse association between intake and risk was limited to women with the GG genotype of the rs4986938 polymorphism for postmenopausal Japanese (odds ratio for highest versus lowest tertile = 0.47; P for trend = 0.01), Japanese Brazilians (odds ratio for highest versus lowest median = 0.31) and non-Japanese Brazilians (odds ratio for consumers versus non-consumers = 0.37) (P for interaction = 0.11, 0.08, and 0.21, respectively). We found no remarkable difference for the other four polymorphisms. Our findings suggest that polymorphisms in the estrogen receptor beta gene may modify the association between isoflavone intake and breast cancer risk.

Perspectives on the soy-breast cancer relation

There has been considerable investigation of the potential for soy foods to reduce risk of breast cancer. Initial enthusiasm for this research was partially based on the historically low incidence rates of breast cancer and high soy food intake in Japan. There are several putative soybean chemopreventive agents, but most cancer research has focused on isoflavones. Isoflavones possess both hormonal and nonhormonal properties relevant to carcinogenesis. Recent epidemiologic analyses indicate that among Asians high soy intake is associated with an approximate one-third reduction in the risk of both pre- and postmenopausal breast cancer. However, several lines of evidence suggest that to derive maximum protection against breast cancer, soy must be consumed early in life. This evidence is consistent with the lack of significant effects noted in clinical studies that have evaluated the effects of isoflavone-containing products on breast cancer risk markers. Isoflavones may exert their putative protective effects by stimulating breast cell differentiation in a manner similar to that which is thought to occur during early pregnancy. Finally, the ability of the isoflavone genistein to stimulate the growth of mammary tumors in ovariectomized athymic nude mice implanted with estrogen-sensitive breast cancer cells has raised concern that soy foods, and especially isoflavone supplements, are contraindicated for patients with breast cancer and women at high risk of breast cancer. However, findings from clinical studies, in which breast biopsies have been taken or breast tissue density measured after isoflavone exposure, are reassuring and contrast with the proliferative effects of conventional combined hormone therapy, although understanding of the effect of soy and isoflavones on breast tissues remains imprecise.

Inflammatory markers in a 2-year soy intervention among premenopausal women

BACKGROUND

Epidemiologic evidence supports a role of soy foods in breast cancer etiology. Because chronic inflammation appears to be a critical component in carcinogenesis, we examined the potential anti-inflammatory effects of soy foods.

METHODS

The original 2-year dietary intervention randomized 220 premenopausal women of whom 183 women (90 in the intervention group and 93 in the control group) were included in the current investigation; 40% were of Asian ancestry. The intervention group consumed two daily soy servings containing 50 mg of isoflavones (aglycone equivalents), whereas the controls maintained their regular diet. Five serum samples obtained at month 0, 3, 6, 12, and 24 were analyzed for interleukin (IL)-6, C-reactive protein (CRP), leptin, and adiponectin by ELISA. For statistical analysis, mixed models were applied to incorporate the repeated measurements.

RESULTS

The levels of all analytes were lower in Asian than Caucasian women. Overweight women had significantly higher levels of CRP, IL-6, and leptin and lower levels of adiponectin than normal weight women. We did not observe a significant effect of soy foods on the four markers, but leptin increased in the control and not in the intervention group (p = 0.20 for group-time effect); this difference was significant for Asian (p = 0.01) and obese women (p = 0.005).

CONCLUSION

During this 2-year intervention, soy foods did not modify serum levels of CRP, IL-6, leptin, and adiponectin in premenopausal women although leptin levels remained stable among women in the intervention group who were obese or of Asian ancestry. Further studies with diverse markers of inflammation are necessary to clarify the specific effect of soy on immune responses.

Childhood soy intake and breast cancer risk in Asian American women

INTRODUCTION

Historically, breast cancer incidence has been substantially higher in the United States than in Asia. When Asian women migrate to the United States, their breast cancer risk increases over several generations and approaches that for U.S. Whites. Thus, modifiable factors, such as diet, may be responsible.

METHODS

In this population-based case-control study of breast cancer among women of Chinese, Japanese, and Filipino descent, ages 20 to 55 years, and living in San Francisco-Oakland (California), Los Angeles (California) and Oahu (Hawaii), we interviewed 597 cases (70% of those eligible) and 966 controls (75%) about adolescent and adult diet and cultural practices. For subjects with mothers living in the United States (39% of participants), we interviewed mothers of 99 cases (43% of eligible) and 156 controls (40%) about the daughter's childhood exposures. Seventy-three percent of study participants were premenopausal at diagnosis.

RESULTS

Comparing highest with lowest tertiles, the multivariate relative risks (95% confidence interval) for childhood, adolescent, and adult soy intake were 0.40 (0.18-0.83; P(trend) = 0.03), 0.80 (0.59-1.08; P(trend) = 0.12), and 0.76 (0.56-1.02; P(trend) = 0.04), respectively. Inverse associations with childhood intake were noted in all three races, all three study sites, and women born in Asia and the United States. Adjustment for measures of westernization attenuated the associations with adolescent and adult soy intake but did not affect the inverse relationship with childhood soy intake.

DISCUSSION

Soy intake during childhood, adolescence, and adult life was associated with decreased breast cancer risk, with the strongest, most consistent effect for childhood intake. Soy may be a hormonally related, early-life exposure that influences breast cancer incidence.

Dietary patterns and breast cancer risk in Asian American women

BACKGROUND

The role of diet as a cause of breast cancer in Asian Americans has not been adequately studied.

OBJECTIVE

We investigated the association between dietary patterns and breast cancer risk in Asian Americans.

DESIGN

This population-based case-control study in Los Angeles County compared dietary patterns between 1248 Asian American women with incident breast cancer and 1148 age-, ethnicity-, and neighborhood-matched controls. The relation between dietary patterns and serum concentrations of estrogens, androgens, and sex hormone-binding globulin (SHBG) was investigated in 2172 postmenopausal control women.

RESULTS

We used a scoring method proposed by Trichopoulou et al (1) and found that adherence to a Mediterranean diet was inversely associated with risk; the odds ratio (OR) was 0.65 (95% CI: 0.44, 0.95) in women with the highest scores (> or = 8; most adherent) compared with those with the lowest scores (0-3; P for trend = 0.009), after adjustment for key covariates. We also used factor analysis and identified 3 dietary patterns (Western-meat/starch, ethnic-meat/starch, and vegetables/soy). In a combined index of the 3 patterns, women who were high consumers of Western and ethnic meat/starch and low consumers of the vegetables/soy diets showed the highest risk (OR: 2.19; 95% CI: 1.40, 3.42; P for trend = 0.0005). SHBG concentrations were 23% lower in women with a high intake of the meat/starch pattern and a low intake of the vegetables/soy pattern than in those with a low intake of the meat/starch pattern and a high intake of the vegetables/soy pattern (P for trend = 0.069).

CONCLUSION

Our results suggest that a diet characterized by a low intake of meat/starches and a high intake of legumes is associated with a reduced risk of breast cancer in Asian Americans.

Facts and fiction of genetically engineered food

The generation of genetically engineered (GE) foods has been raising several concerns and controversies that divide not only the general public but also the scientific community. The fear and importance of the new technology, as well as commercial interests, have supported many of the ongoing discussions. The recent increase in the number of GE foods approved for import into the European Union and the increasingly global commercial food trades justify revisiting the facts and fiction surrounding this technology with the aim of increasing public awareness for well-informed decisions. Techniques that have recently become available for assessing food quality and its impact on human health, as well as the wealth of scientific data previously generated, clearly support the safety of commercialized GE products.

Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis

BACKGROUND

Hormonal effects of soy and isoflavones have been investigated in numerous trials with equivocal findings. We aimed to systematically assess the effects of soy and isoflavones on circulating estrogen and other hormones in pre- and post-menopausal women.

METHODS

The Cochrane Library, MEDLINE and EMBASE (plus reviews and experts) were searched to December 2007. Inclusion of randomized or residential crossover trials of soy or isoflavones for 4 or more weeks on estrogens, SHBG, FSH, LH, progesterone and thyroid hormones in women was assessed independently in duplicate. Six percent of papers assessed were included. Data concerning participants, interventions, outcomes, potential effect modifiers and trial quality characteristics were extracted independently in duplicate.

RESULTS

Forty-seven studies (11 of pre-, 35 of post- and 1 of perimenopausal women) were included. In premenopausal women, meta-analysis suggested that soy or isoflavone consumption did not affect primary outcomes estradiol, estrone or SHBG concentrations, but significantly reduced secondary outcomes FSH and LH [by ∼20% using standardized mean difference (SMD), P = 0.01 and 0.05, respectively]. Menstrual cycle length was increased by 1.05 days (95% CI 0.13, 1.97, 10 studies). In post-menopausal women, there were no statistically significant effects on estradiol, estrone, SHBG, FSH or LH, although there was a small statistically non-significant increase in total estradiol with soy or isoflavones (∼14%, SMD, P = 0.07, 21 studies).

CONCLUSIONS

Isoflavone-rich soy products decrease FSH and LH in premenopausal women and may increase estradiol in post-menopausal women. The clinical implications of these modest hormonal changes remain to be determined.

Isoflavone consumption and subsequent risk of hepatocellular carcinoma in a population-based prospective cohort of Japanese men and women

The incidence of hepatocellular carcinoma (HCC) is much higher in men than in women. Several experiment and epidemiological studies have suggested that estrogen might play an inhibitory role in the development of HCC. Because isoflavones have a similar structure as 17beta-estradiol and appear to have an anti-estrogenic effect in women and estrogenic effect in men, we hypothesized that the effect of isoflavones on HCC differs by sex. We investigated the association between isoflavones (genistein and daidzein) and soy products and HCC in Japan in a population-based prospective study in 19,998 Japanese (7,215 men and 12,783 women) aged 40-69 years. During 11.8 years of follow-up, 101 subjects (69 men and 32 women) were newly diagnosed with HCC. Case patients were grouped according to consumption of isoflavones and soy products and stratified by hepatitis virus infection. Hazard ratios (HRs) and 95% confidence intervals (CIs) for HCC were calculated by Cox proportional-hazards modeling. In women, genistein and daidzein were dose-dependently associated with an increased risk of HCC, with multivariable HRs for the highest versus lowest tertile of 3.19 (95%CI = 1.13-9.00, p(trend) = 0.03) and 3.90 (95% CI = 1.30-11.69, p(trend) = 0.01), respectively. No association between isoflavones and HCC was observed in men. These results persisted when analysis was restricted to subjects positive for either or both hepatitis C and B virus. In conclusion, isoflavone consumption may be associated with an increased risk of HCC in women. Women with hepatitis virus infection may be advised to abstain from isoflavone consumption. Further studies are warranted to confirm these findings.

Soy isoflavones modulate azoxymethane-induced rat colon carcinogenesis exposed pre- and postnatally and inhibit growth of DLD-1 human colon adenocarcinoma cells by increasing the expression of estrogen receptor-beta

We studied the effects of lifetime exposure to dietary soy isoflavones in an azoxymethane (AOM)-induced rat colon cancer model. Male pups born to Sprague-Dawley rats exposed (including during pregnancy and lactation) to soy isoflavones at either no (0 mg = control), low (40 mg), or high (1000 mg) doses/kg diet were weaned and continued receiving their respective parental diets until the end of the study. Weaned rats received 2 subcutaneous injections (15 mg/kg body weight) of AOM 1 wk apart. After 26 wk, rats were killed and the coordinates of colon aberrant crypt foci (ACF) and tumors were determined. Expression of estrogen receptor (ER)-beta was assessed in rat colon tumors and in DLD-1 human colon adenocarcinoma cells exposed to soy isoflavones. Compared with the control, soy isoflavones did not affect incidences or multiplicities of colon ACF or tumors. Low-dose soy isoflavones decreased tumor burden and size compared with the control (P < 0.05). Expression of ERbeta increased in colon tumors of soy isoflavone-treated groups compared with the control. Soy isoflavones dose-dependently arrested the growth of DLD-1 cells and at subcytotoxic levels increased the expression of ERbeta. Our results suggest that pre- and postnatal exposure to dietary soy isoflavones suppresses the growth of colon tumors in male rats. The overexpression of ERbeta in both rat colon tumors and DLD-1 cells caused by soy isoflavones suggests that ERbeta is a critical mediator in mitigating its cancer-preventive effects.

Isoflavones - Mechanism of Action and Impact on Breast Cancer Risk

Isoflavones are plant-derived substances with weak es-trogenic effects. Asian populations are high consumers of soy products which are rich in isoflavones. The lower breast cancer incidence in Asian women compared with Western women has been associated with the possibility of a preventive isoflavone effect on cancer risk. The aim of this review is to give an overview of current research data on the influence of isoflavones on the risk of primary breast cancer development as well as the risk of recurrence in breast cancer patients. Despite inconsistencies in the available data, an inverse correlation between isoflavone intake and risk of breast cancer is likely. However, a negative impact on breast cancer disease, especially on hormone receptor-positive tumors, cannot be excluded at present.

Green tea, soy, and mammographic density in Singapore Chinese women

There is increasing evidence from observational studies that breast cancer risk is inversely associated with soy and green tea consumption. We investigated the effects of these two dietary agents on mammographic density, a well-established biomarker for breast cancer risk, in a cross-sectional analysis of mammograms and validated food frequency questionnaires from 3,315 Chinese women in Singapore. Percent mammographic density (PMD) was assessed using a reproducible computer-assisted method. We used generalized linear models to estimate PMD by intake of soy, green tea, and black tea while adjusting for potential confounders. Daily green tea drinkers showed statistically significantly lower PMD (19.5%) than non-tea drinkers (21.7%; P = 0.002) after adjusting for relevant covariates. This difference in PMD between daily green tea drinkers and non-tea drinkers remained statistically significant after adjustment for soy (P = 0.002); the effect was more apparent among lower soy consumers (Q1-Q3; 21.9% versus 19.4%; P = 0.002) than in higher (Q4) consumers (20.9% versus 19.5%; P = 0.32). Black tea intake was unrelated to PMD. Only among postmenopausal women who reported very high soy intake (Q4) compared with those with less soy intake was there any association noted between PMD and soy intake (18.9% versus 20.5%; P = 0.035). Following adjustment for green tea intake, the association between soy and PMD was no longer statistically significant (P = 0.52). Our findings suggest that both regular green tea and high soy intake may have beneficial effects on the breast; the effect of green tea on PMD may be stronger than the effect of soy.

Sample preparation for the analysis of isoflavones from soybeans and soy foods

This manuscript provides a review of the actual state and the most recent advances as well as current trends and future prospects in sample preparation and analysis for the quantification of isoflavones from soybeans and soy foods. Individual steps of the procedures used in sample preparation, including sample conservation, extraction techniques and methods, and post-extraction treatment procedures are discussed. The most commonly used methods for extraction of isoflavones with both conventional and "modern" techniques are examined in detail. These modern techniques include ultrasound-assisted extraction, pressurized liquid extraction, supercritical fluid extraction and microwave-assisted extraction. Other aspects such as stability during extraction and analysis by high performance liquid chromatography are also covered.

Soy consumption and histopathologic markers in breast tissue using tissue microarrays

This study examined the relation of soy intake with hormonal and proliferation markers in benign and malignant breast tissue using tissue microarrays (TMAs). TMAs with up to 4 malignant and 4 benign tissue samples for 268 breast cancer cases were constructed. Soy intake in early life and in adulthood was assessed by questionnaire. The TMAs were stained for estrogen receptor (ER) alpha, ERbeta, progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2/neu), proliferating cell nuclear antigen (PCNA), and Ki-67 using standard immunohistochemical methods. Logistic regression was applied for statistical analysis. A higher percentage of women showed positive marker expression in malignant than in benign tissue. With one exception, HER2/neu, no significant associations between soy intake and pathologic markers were observed. Early life soy intake was associated with lower HER2/neu and PCNA staining of malignant tissue. In benign tissue, early life soy intake showed higher ER and PR expression, but no difference in proliferation markers. The results of this investigation provide some assurance that soy intake does not adversely affect markers of proliferation. TMAs were shown to be a useful tool for epidemiologic research.

Early intake appears to be the key to the proposed protective effects of soy intake against breast cancer

There is a large variation in breast cancer incidence and mortality rates worldwide. Migration studies have indicated that this variation is primarily the result of lifestyle influences. Although there has been much research conducted, definitively identifying dietary factors that impact breast cancer risk has proven difficult. In part this may be because most clinical and epidemiologic studies have focused on adult dietary exposure. However, evidence suggests that childhood and/or adolescence is the period of life when the breast is most sensitive to dietary influences. Further, the available epidemiologic and animal data suggest that early soy intake reduces breast cancer risk. Soy foods are unique dietary sources of isoflavones, diphenolic compounds that exert estrogen-like effects under certain experimental conditions. The protection effects of soy may result from the soybean isoflavones stimulating differentiation of the breast in much the same way that the elevated estrogen levels do during pregnancy. More specifically, in rats, the primary isoflavone genistein reduces mammary tumorigenesis and increases mammary tissue differentiation by leading to a reduction in the number of terminal end buds (TEB) and an increase in the number of differentiated lobules. There is need and justification for continued investigation of the early soy intake hypothesis, particularly to determine the cellular targets of soy action and to identify the signaling pathways mediating the effects on mammary gland morphology and susceptibility to breast cancer.

Phytoestrogenic isoflavonoids in epidemiologic and clinical research

Isoflavones (IFLs) are natural products to which humans have been traditionally exposed predominantly through soy foods; more recently humans are also exposed to them through soy protein addition to processed foods or through supplements. They are structurally similar to steroidal estrogens and can exert estrogenic or antiestrogenic effects depending on their concentrations and on the tissue considered. These properties qualify IFLs to be classified as phytoestrogens and are believed to account for many of the biological effects observed for soy and/or IFL exposure including benefits for bone and heart health or prevention of menopausal symptoms and certain types of cancer. In order to evaluate the function of IFLs, alone or when exposure happens through soy intake, pharmacokinetics and bioavailability are critical issues to be considered in epidemiologic and clinical research. For this purpose precise, accurate, robust, fast, and affordable techniques for IFL analyses are required.

Soy protein containing isoflavones and mammographic density in a randomized controlled trial in postmenopausal women

BACKGROUND

The relatively high dietary intake of soy in Asian countries has been hypothesized to, at least partly, explain the lower breast cancer incidence patterns in these countries compared with the Western world. The aim of the present study was to determine the effect of daily soy supplementation on mammographic density, one of the strongest known risk factors for breast cancer.

METHODS

A double-blind, randomized, controlled trial was conducted to compare the effects of soy protein intake containing 99 mg isoflavones daily with intake of milk protein (placebo) for the duration of 1 year. Two hundred and two Dutch postmenopausal women ages 60 to 75 years were randomized. Mammographic density was assessed using a quantitative computer-assisted method on digitized mammograms. Equol producer status was assessed in plasma provided at the final visit (soy group) or after a 3-day challenge with soy after the trial was finished (placebo group).

RESULTS

A total of 175 women completed the baseline visits and at least one follow-up visit and were included in the intention-to-treat analyses. For 126 women, both pre- and post-trial mammograms were available. Mammographic density decreased in both study arms, but the decrease did not differ significantly between intervention and placebo groups. Equol producer status did not modify the results.

CONCLUSION

The results of this trial do not support the hypothesis that a diet high in soy protein among postmenopausal women decreases mammographic density.

Effects of prior oral contraceptive use and soy isoflavonoids on estrogen-metabolizing cytochrome P450 enzymes

Estrogen exposure and metabolism may play an important role in the development of estrogen-sensitive cancers in postmenopausal women. In this study we investigated whether past oral contraceptive (OC) administration or current dietary isoflavonoids (IF) affected expression and/or activity of steroid hormone-metabolizing cytochrome P450 (CYP) enzymes using complementary primate and cell culture models. One-hundred-eighty-one female cynomolgus macaques were randomized to receive OC or nothing for 26 months premenopausally, then ovariectomized and randomized to one of three diets for 36 months: an IF-depleted soy protein isolate (Soy-) diet, a Soy diet with IF (Soy+), or a Soy- diet supplemented with conjugated equine estrogens (CEE). Prior OC-treatment significantly reduced CYP gene expression in the mammary gland (< or =60% of OC-). Dietary IFs had no effect on CYP expression, while CEE-treatment decreased CYP1A1 and increased CYP3A4 mRNA in a tissue-specific manner. For in vitro studies, we measured effects of the isoflavonoids genistein, daidzein and equol on CYP activity using intact V79 cells stably transfected to express CYP1A1, CYP1B1, or CYP3A4. All three IFs significantly altered CYP activity in a dose-dependent and isoform-specific manner (20-95% inhibition versus controls). These results suggest potential mechanisms for prior OC and dietary IF effects on cancer risk in estrogen-responsive tissues.

Estrogenic status modulates the effect of soy on hepatic responses to 7,12-dimethylbenz(a)anthracene (DMBA)

We examined the influence of estradiol (E2) status and soy protein isolate (SPI) intake on the hepatic responses altered by 7,12-dimethylbenz(a)anthracene (DMBA, a polycyclic aromatic hydrocarbon [PAH]). Sprague-Dawley rats were ovariectomized (OVX) at PND50 and infused with E2 or vehicle for 14 d and gavaged with 50 mg/kg DMBA or vehicle 24 h before sacrifice at PND64. Rats were fed an AIN-93G diet made with SPI or casein as sole protein source throughout the study. Basal AhR protein levels were reduced (P<0.05) by SPI feeding irrespective of the E2 status. However, DMBA increased (P<0.05) AhR-induced CYP1A1 gene expression in OVX, SPI-fed rats, but reduced (P<0.05) CYP1A1 in OVX+E2, SPI-fed rats. Chromatin-immunoprecipitation demonstrated lower (P<0.05) DMBA-mediated recruitment of estrogen receptor alpha to the CYP1A1 promoter by SPI feeding in the presence of E2, suggesting an estrogen-like action of SPI on DMBA-mediated signaling in the absence of E2. Further, microarray analysis (Rat 230-2.0 Affymetrix-GeneChip) revealed 231 genes common to SPI+DMBA and SPI+E2+DMBA (normalized to E2) treatments. AhR-activated genes (CYP1A1, CYP1A2, and NQO1) were down-regulated by SPI+E2+DMBA compared to SPI+DMBA. Unique interactions among SPI, DMBA and E2 altered the expression profile of 316 genes, not observed by either treatment alone. Our data suggest that although E2 status does not effect soy-mediated AhR degradation, it modulates the effects of soy on many genes, including CYP1A1.

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

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.

Soy intake and breast cancer risk in Singapore Chinese Health Study

We investigated the effects of soy isoflavone intake on breast cancer in a prospective study of 35 303 Singapore Chinese women enrolled during April 1993 to December 1998 in the Singapore Chinese Health Study. At recruitment, each subject was personally administered a validated semiquantitative food frequency questionnaire covering 165 food and beverage items. As of December 31 2005, 629 had developed breast cancer following an accumulation of 338 242 person-years. Using Cox regression and adjusting for age at interview, year of interview, dialect group, education, family history of breast cancer, age when periods became regular, parity, menopausal status, body mass index (BMI), n-3 fatty acid, and other covariates, we found breast cancer risk was reduced significantly in association with high soy intake. Relative to women with lower (below median) soy intake (<10.6 mg isoflavone per 1000 Kcal), women with higher (above median) intake showed a significant 18% risk reduction (relative risk (RR)=0.82, 95% confidence interval (CI)=0.70–0.97). This inverse association was apparent mainly in postmenopausal women (RR=0.74, 95% CI=0.61–0.90), and was not observed in premenopausal women (RR=1.04, 95% CI=0.77–1. 40). Among postmenopausal women, the soy–breast cancer association was stronger in those above median BMI (RR=0.67, 95% CI=0.51–0.88) than in leaner women (RR=0.83, 95% CI=0.62–1.11). Duration of follow-up modified the soy–breast cancer association, the effect being twice as large among women with 10+ vs fewer years of follow-up. Neither oestrogen nor progesterone receptor status of the tumours materially influenced the association. These prospective findings suggest that approximately 10 mg of isoflavones per day, obtained in a standard serving of tofu, may have lasting beneficial effects against breast cancer development.

Do phytoestrogens reduce the risk of breast cancer and breast cancer recurrence? What clinicians need to know

Oestrogen is an important determinant of breast cancer risk. Oestrogen-mimicking plant compounds called phytoestrogens can bind to oestrogen receptors and exert weak oestrogenic effects. Despite this activity, epidemiological studies suggest that the incidence of breast cancer is lower in countries where the intake of phytoestrogens is high, implying that these compounds may reduce breast cancer risk, and possibly have an impact on survival. Isoflavones and lignans are the most common phytoestrogens in the diet. In this article, we present findings from human observational and intervention studies related to both isoflavone and lignan exposure and breast cancer risk and survival. In addition, the clinical implications of these findings are examined in the light of a growing dietary supplement market. An increasing number of breast cancer patients seek to take supplements together with their standard treatment in the hope that these will either prevent recurrence or treat their menopausal symptoms. Observational studies suggest a protective effect of isoflavones on breast cancer risk and the case may be similar for increasing lignan consumption although evidence so far is inconsistent. In contrast, short-term intervention studies suggest a possible stimulatory effect on breast tissue raising concerns of possible adverse effects in breast cancer patients. However, owing to the dearth of human studies investigating effects on breast cancer recurrence and survival the role of phytoestrogens remains unclear. So far, not enough clear evidence exists on which to base guidelines for clinical use, although raising patient awareness of the uncertain effect of phytoestrogens is recommended.

Soy isoflavones, estrogen therapy, and breast cancer risk: analysis and commentary

There has been considerable investigation of the potential for soyfoods to reduce risk of cancer, and in particular cancer of the breast. Most interest in this relationship is because soyfoods are essentially a unique dietary source of isoflavones, compounds which bind to estrogen receptors and exhibit weak estrogen-like effects under certain experimental conditions. In recent years the relationship between soyfoods and breast cancer has become controversial because of concerns – based mostly on in vitro and rodent data – that isoflavones may stimulate the growth of existing estrogen-sensitive breast tumors. This controversy carries considerable public health significance because of the increasing popularity of soyfoods and the commercial availability of isoflavone supplements. In this analysis and commentary we attempt to outline current concerns regarding the estrogen-like effects of isoflavones in the breast focusing primarily on the clinical trial data and place these concerns in the context of recent evidence regarding estrogen therapy use in postmenopausal women. Overall, there is little clinical evidence to suggest that isoflavones will increase breast cancer risk in healthy women or worsen the prognosis of breast cancer patients. Although relatively limited research has been conducted, and the clinical trials often involved small numbers of subjects, there is no evidence that isoflavone intake increases breast tissue density in pre- or postmenopausal women or increases breast cell proliferation in postmenopausal women with or without a history of breast cancer. The epidemiologic data are generally consistent with the clinical data, showing no indication of increased risk. Furthermore, these clinical and epidemiologic data are consistent with what appears to be a low overall breast cancer risk associated with pharmacologic unopposed estrogen exposure in postmenopausal women. While more research is required to definitively allay concerns, the existing data should provide some degree of assurance that isoflavone exposure at levels consistent with historical Asian soyfood intake does not result in adverse stimulatory effects on breast tissue.

The role of early life genistein exposures in modifying breast cancer risk

Review of the existing literature suggests that consumption of soy foods or an exposure to a soy isoflavone genistein during childhood and adolescence in women, and before puberty onset in animals, reduces later mammary cancer risk. In animal studies, an exposure that is limited to the fetal period or adult life does not appear to have the same protective effect. A meta-analysis of human studies indicates a modest reduction in pre- and postmenopausal risk when dietary intakes are assessed during adult life. These findings concur with emerging evidence indicating that timing may be vitally important in determining the effects of various dietary exposures on the susceptibility to develop breast cancer. In this review, we address the mechanisms that might mediate the effects of an early life exposure to genistein on the mammary gland. The focus is on changes in gene expression, such as those involving BRCA1 and PTEN. It will be debated whether mammary stem cells are the targets of genistein-induced alterations and also whether the alterations are epigenetic. We propose that the effects on mammary gland morphology and signalling pathways induced by pubertal exposure to genistein mimic those induced by the oestrogenic environment of early first pregnancy.

Early life and adult exposure to isoflavones and breast cancer risk

Soy and red-clover isoflavones are commonly consumed within the diet or as a dietary supplement due to a range of presumed beneficial health benefits. These isoflavones are thought to protect against heart diseases as well as breast and other types of cancer. Isoflavones are structurally similar to estrogens and may act as estrogen agonists or antagonists by binding to estrogen receptors. Because of an increased use of isoflavones in processed foods and dietary supplements as well as the greater consumption of soy products, dietary intakes of isoflavones are increasing in children and adolescents in North America. Estrogens are a known component of numerous hormone related cancers including breast cancer. It is with these facts in mind that we review the existing epidemiological and experimental animal studies for a resolution to a proposed correlation between increased isoflavone consumption and breast cancer. There is conflicting evidence from epidemiological, intervention and experimental animal studies regarding the chemopreventing effects of soy isoflavones in breast cancer. Isoflavones are weak estrogens and their effect depends upon the dose, time of exposure and species involved. It would, therefore, not be safe to indisputably accept soy or red-clover as a source of isoflavone resource to prevent breast cancer.