Consumption of soy foods and the risk of breast cancer: findings from the Japan Collaborative Cohort (JACC) Study

Intake of Soy, Soy Isoflavones and Soy Protein and Risk of Cancer Incidence and Mortality

Background and Aims

Associations between soy intake and risk of cancer have been evaluated in prospective observational studies with inconsistent results. Whether the potential anticancer effects offered by soy were attributed to soy isoflavones and soy protein still needs to be elucidated. This study aimed to comprehensively quantify the association of soy, soy isoflavones and soy protein intake with risk of cancer incidence and cancer mortality by conducting a meta-analysis of all available studies.

Methods

PubMed, Embase, Web of Science, and Cochrane Library databases were searched up to 16 September 2021. Prospective cohort studies that examined the effect of soy, soy isoflavones and soy protein on cancer incidence and cancer mortality were identified. Random-effects models were used to pool the multivariable-adjusted relative risks (RRs) and corresponding 95% confidence intervals (CIs). The potential dose-response relations were explored by using generalized least-squares trend estimation.

Results

Eighty one prospective cohort studies were included in the meta-analysis. A higher intake of soy was significantly associated with a 10% reduced risk of cancer incidence (RR, 0.90; 95% CI, 0.83–0.96). Each additional 25 g/d soy intake decreased the risk of cancer incidence by 4%. Intake of soy isoflavones was inversely associated with risk of cancer incidence (RR, 0.94; 95% CI, 0.89–0.99), whereas no significant association was observed for soy protein. The risk of cancer incidence was reduced by 4% with each 10 mg/d increment of soy isoflavones intake. Similar inverse associations were also found for soy in relation to site-specific cancers, particularly lung cancer (RR, 0.67; 95%CI, 0.52–0.86) and prostate cancer (RR, 0.88; 95%CI, 0.78–0.99). However, high intake of soy, soy isoflavones and soy protein were not associated with cancer mortality.

Conclusions

Higher intake of soy and soy isoflavones were inversely associated with risk of cancer incidence, which suggested that the beneficial role of soy against cancer might be primarily attributed to soy isoflavones. These findings support recommendations to include soy as part of a healthy dietary pattern for the prevention of cancer.

Risk Factors for Female Breast Cancer: A Population Cohort Study

Simple Summary

In recent years, it has been emphasized that the development of a healthy lifestyle can prevent the incidence of cancer, and several recent studies on female breast cancer (BC) have also become interested in sedentary behavioral issues. Our prospective cohort study found that, in addition to the currently known risk factors (RFs) such as parity and body mass index (BMI), which affect the probability of developing BC in women, a sedentary lifestyle and drinking sugar-sweetened beverages (SSB) can cause BC. Therefore, we propose that the modifiable risk profiles of sedentary behavior and sugary beverage consumption may also be associated with increased incidence of female BC in the Taiwanese population.

Abstract

Background: The incidence of female BC among the Eastern and Southeastern Asian populations has gradually increased in recent years. However, epidemiological studies on the relationship between a sedentary lifestyle and female BC are insufficient. In order to determine the association between this lifestyle and the incidence of female BC, we conducted a population-based cohort study on women in Taiwan. Methods: We followed a prospective cohort of 5879 women aged 30 years and over enrolled in the 2001 National Health Interview Survey (NHIS), who developed female BC over a period of 72,453 person years, and we estimated the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) using the Cox proportional hazards model. Results: RFs associated with female BC incidence included parity (adjusted HR = 0.63; 95% CI: 0.44–0.91), body mass index (adjusted HR = 1.34; 95% CI: 1.04–1.71), and ≥3 h/day spent sitting (adjusted HR = 1.89; 95% CI: 1.08–3.32). The incidence of female BC in participants who sat for ≥3 h/day and consumed sugary drinks was 2.5 times greater than that in those who sat for <3 h/day and did not consume sugary drinks (adjusted HR = 2.51; 95% CI: 1.01–6.23). Conclusions: The findings of this study indicate that sedentary behavior and sugary drink intake may increase the risk of developing female BC. These are modifiable RFs; therefore, a healthy lifestyle and diet can reduce the incidence of female BC.

Endocrine disrupting chemicals and breast cancer: a systematic review of epidemiological studies

BACKGROUND

Endocrine-disrupting compounds (EDCs) are ubiquitous substances that are found in our everyday lives, including pesticides, plasticizers, pharmaceutical agents, personal care products, and also in food products and food packaging. Increasing epidemiological evidence suggest that EDCs may affect the development or progression of breast cancer and consequently lead to lifelong harmful health consequences, especially when exposure occurs during early life in humans. Yet so far no appraisal of the available evidence has been conducted on this topic.

OBJECTIVE

To systematically review all the available epidemiological studies about the association of the levels of environmental exposures of EDCs with breast cancer risk.

METHODS

The search was performed in accordance with the PRISMA guidelines. We retrieved articles from PubMed (MEDLINE) until 10 March 2021. The key words used in this research were: "Endocrine disruptor(s)" OR "Endocrine disrupting chemical(s)" OR any of the EDCs mentioned below AND "Breast cancer" to locate all relevant articles published. We included only cohort studies and case-control studies. All relevant articles were accessed in full text and were evaluated and summarized in tables.

RESULTS

We identified 131 studies that met the search criteria and were included in this systematic review. EDCs reviewed herein included pesticides (e.g. p,p'-dichlorodiphenyltrichloroethane (DDT), p,p'-dichlorodiphenyldichloroethylene (DDE), atrazine, 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD or dioxin)), synthetic chemicals (e.g. bisphenol A (BPA), phthalates, per- and polyfluoroalkyl substances (PFAS), parabens, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), contraceptive pills), phytoestrogens (e.g. genistein, resveratrol), and certain mycotoxins (e.g. zearalenone). Most studies assessed environmental EDCs exposure via biomarker measurements.

CONCLUSION

We identified certain EDC exposures could potentially elevate the risk of breast cancer. As majority of EDCs are highly persistent in the environment and bio-accumulative, it is essential to assess the long-term impacts of EDC exposures, especially multi-generational and transgenerational. Also, since food is often a major route of exposure to EDCs, well-designed exposure assessments of potential EDCs in food and food packing are necessary and their potential link to breast cancer development need to be carefully evaluated for subsequent EDC policy making and regulations.

The Vascular Effects of Isolated Isoflavones-A Focus on the Determinants of Blood Pressure Regulation

Isoflavones are phytoestrogen compounds with important biological activities, including improvement of cardiovascular health. This activity is most evident in populations with a high isoflavone dietary intake, essentially from soybean-based products. The major isoflavones known to display the most important cardiovascular effects are genistein, daidzein, glycitein, formononetin, and biochanin A, although the closely related metabolite equol is also relevant. Most clinical studies have been focused on the impact of dietary intake or supplementation with mixtures of compounds, with only a few addressing the effect of isolated compounds. This paper reviews the main actions of isolated isoflavones on the vasculature, with particular focus given to their effect on the determinants of blood pressure regulation. Isoflavones exert vasorelaxation due to a multitude of pathways in different vascular beds. They can act in the endothelium to potentiate the release of NO and endothelium-derived hyperpolarization factors. In the vascular smooth muscle, isoflavones modulate calcium and potassium channels, leading to hyperpolarization and relaxation. Some of these effects are influenced by the binding of isoflavones to estrogen receptors and to the inhibition of specific kinase enzymes. The vasorelaxation effects of isoflavones are mostly obtained with plasma concentrations in the micromolar range, which are only attained through supplementation. This paper highlights isolated isoflavones as potentially suitable alternatives to soy-based foodstuffs and supplements and which could enlarge the current therapeutic arsenal. Nonetheless, more studies are needed to better establish their safety profile and elect the most useful applications.

Fermented and nonfermented soy foods and the risk of breast cancer in a Japanese population-based cohort study

Background

Although preclinical studies suggest that fermented soy foods may have a protective effect against breast cancer, no prospective cohort studies have examined this association.

Objective

Our study examined the association between fermented and nonfermented soy food intake and breast cancer risk using a population‐based prospective cohort study in Japan.

Methods

We included a total of 47,614 women aged 45–74 years in an analysis of the Japan Public Health Center‐based Prospective Study (JPHC Study). A validated food frequency questionnaire (FFQ) was used for the assessment of dietary intake. Breast cancer incidence was analyzed by multivariate Cox proportional hazards regression models.

Results

During an average of 15.5 years of follow‐up, 825 breast cancer cases were newly identified. We found no association of intake of soy foods with breast cancer risk, regardless of fermentation, with multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) for the highest quartiles of fermented and nonfermented soy food intake of 0.94 (0.67, 1.32) and 1.15 (0.85, 1.57) compared with the lowest quartile (p for trend = 0.305 and 0.393). Unlike nonfermented soy, higher intake of fermented soy foods was associated with a significant decrease in the risk of nonlocalized breast cancer. The HR and 95% CI in the highest compared to lowest intake category of fermented soy foods was 0.53 (0.28, 0.99) versus nonfermented soy foods 0.85 (0.51, 1.42) (p for trend = 0.026 and 0.797).

Conclusions

Our analyses showed that fermented soy foods had no association with overall breast cancer but may be associated with decreased risk of nonlocalized breast cancer.

Intake of Various Food Groups and Risk of Breast Cancer: A Systematic Review and Dose-Response Meta-Analysis of Prospective Studies

Despite increasing evidence for the association of food-based dietary patterns with breast cancer risk, knowledge about the shape of the relationship and the quality of meta-evidence are insufficient. We aimed to summarize the associations between food groups and risks of breast cancer. We performed a systematic literature search of the PubMed and Embase databases up to March 2020. We included cohort, case-cohort, nested case-control studies, and follow-up studies of randomized controlled trials that investigated the relationship between breast cancer risk and at least 1 of the following food groups: red meat, processed meat, fish, poultry, egg, vegetables, fruit, dairy product (overall, milk, yogurt, and cheese), grains/cereals, nuts, legumes, soy, and sugar-sweetened beverages. Summary risk ratios (RRs) and 95% CIs were estimated using a random-effects model for linear and nonlinear relationships. Inverse linear associations were observed for vegetables (RR per 100 g/d, 0.97; 95% CI, 0.95-0.99), fruit (RR per 100 g/d, 0.97; 95% CI, 0.95-0.99), cheese (RR per 30 g/d, 0.95; 95% CI, 0.91-1.00), and soy (RR per 30 g/d, 0.96; 95% CI, 0.94-0.99), while positive associations were observed for red (RR per 100 g/d, 1.10; 95% CI, 1.03-1.18) and processed meat (RR per 50 g/d, 1.18; 95% CI, 1.04-1.33). None of the other food groups were significantly associated with breast cancer risk. A nonlinear association was observed only for milk, such that the intake of >450 g/d increased the risk, while no association was observed for lower intake amounts. High intakes of vegetables, fruit, cheese, and soy products and low intakes of red and processed meat were associated with lower risks of breast cancer. However, causality cannot be inferred from these statistical correlations.

Soy intake and chronic disease risk: findings from prospective cohort studies in Japan

There has been much interest in the potential role of soy in reducing the risk of chronic diseases. Soy foods are uniquely rich in isoflavones, a fact that has triggered much research including intervention studies. However, there have been few long-term prospective observational studies that include disease itself as an outcome. High intake of soy foods is intrinsic to the Japanese diet, which can be advantageous for conducting such studies in Japan. The present report reviews the findings from Japanese prospective cohort studies on soy intake and the risk of cardiovascular diseases, cancer, type 2 diabetes, osteoporosis, menopausal symptoms, and dementia. The results suggest a beneficial role of soy in several chronic diseases, but they are not without controversy. Discrepancies have been observed in the findings of studies of Japanese or other Asians as compared to those of non Asians. This review discusses the issues to be explored in future studies.

Soy intake and breast cancer risk: a prospective study of 300,000 Chinese women and a dose-response meta-analysis

Epidemiological evidence on the association of soy intake with breast cancer risk is still inconsistent due to different soy intake levels across previous studies and small number of breast cancer cases. We aimed to investigate this issue by analyzing data from the China Kadoorie Biobank (CKB) study and conducting a dose-response meta-analysis to integrate existing evidence. The CKB study included over 300,000 women aged 30-79 from 10 regions across China enrolled between 2004 and 2008, and followed-up for breast cancer events until 31 December 2016. Information on soy intake was collected from baseline, two resurveys and twelve 24-h dietary recalls. We also searched for relevant prospective cohort studies to do a dose-response meta-analysis. The mean (SD) soy intake was 9.4 (5.4) mg/day soy isoflavones among CKB women. During 10 years of follow-up, 2289 women developed breast cancers. The multivariable-adjusted relative risk was 1.00 (95% confidence interval [CI] 0.81-1.22) for the fourth (19.1 mg/day) versus the first (4.5 mg/day) soy isoflavone intake quartile. Meta-analysis of prospective studies found that each 10 mg/day increment in soy isoflavone intake was associated with a 3% (95% CI 1-5%) reduced risk of breast cancer. The CKB study demonstrated that moderate soy intake was not associated with breast cancer risk among Chinese women. Higher amount of soy intake might provide reasonable benefits for the prevention of breast cancer.

Tofu intake is inversely associated with risk of breast cancer: A meta-analysis of observational studies

Observational studies on the association between tofu intake and breast cancer incidence have reported inconsistent results. We reviewed the current evidence and quantitatively assessed this association by conducting a dose-response meta-analysis. The electronic databases PubMed and EMBASE were searched for relevant studies published up to August, 2018. We included epidemiological studies that reported relative risks (RRs) or odds ratios (ORs) with 95% confidence intervals (CIs) for the association between tofu intake and breast cancer risk. A total of 14 studies (2 cohort studies, 12 case-control studies) were included in the meta-analysis. The overall OR of breast cancer for highest vs lowest intake of tofu was 0.78 (95% CI 0.69–0.88), with moderate heterogeneity (P = 0.011, I² = 49.7%). Dose-response analysis based on 5 case-control studies revealed that each 10 g/d increase in tofu intake was associated with 10% reduction in the risk of breast cancer (95% CI 7%–13%, P = 0.037, I² = 40.8%). In summary, our findings suggest an inverse dose-response association between tofu intake and risk of breast cancer. However, owing to the limitations of case-control studies, more properly designed prospective studies are warranted to confirm this association.

Boric Acid Activation of eIF2α and Nrf2 Is PERK Dependent: a Mechanism that Explains How Boron Prevents DNA Damage and Enhances Antioxidant Status

Boron is abundant in vegetables, nuts, legumes, and fruit and intake is associated with reduced risk of cancer and DNA damage and increased antioxidant status. Blood boric acid (BA) levels are approximately 10 μM BA in men at the mean US boron intake. Treatment of DU-145 human prostate cancer cells with 10 μM BA stimulates phosphorylation of elongation initiation factor 2α (eIF2α) at Ser51 leading to activation of the eIF2α/ATF4 pathway which activates the DNA damage-inducible protein GADD34. In the present study, we used MEF WT and MEF PERK (±) cells to test the hypothesis that BA-activated eIF2α phosphorylation requires protein kinase RNA-like endoplasmic reticulum kinase (PERK) and activates Nrf2 and the antioxidant response element (ARE). BA (10 μM) increased phosphorylation of eIF2α Ser51 in MEF WT cells at 1 h, but not in MEF Perk -/- cells exposed for as long as 6 h. GCN2 kinase-dependent phosphorylation of eIF2α Ser51 was activated in MEF PERK -/- cells by amino acid starvation. Nrf2 phosphorylation is PERK dependent and when activated is translocated from the cytoplasm to the nucleus where it acts as a transcription factor for ARE. DU-145 cells were treated with 10 μM BA and Nrf2 measured by immunofluorescence. Cytoplasmic Nrf2 was translocated to the nucleus at 1.5-2 h in DU-145 and MEF WT cells, but not MEF PERK -/- cells. Real-time PCR was used to measure mRNA levels of three ARE genes (HMOX-1, NQO1, and GCLC). Treatment with 10 μM BA increased the mRNA levels of all three genes at 1-4 h in DU-145 cells and HMOX1 and GCLC in MEF WT cells. These results extend the known boric acid signaling pathway to ARE-regulated genes. The BA signaling pathway can be expressed using the schematic [BA + cADPR → cADPR-BA → [[ER]_i Ca²⁺↓] → 3 pathways: PERK/eIF2αP → pathways ATF4 and Nrf2; and [[ER]_i Ca²⁺↓] → ER stress → ATF6 pathway. This signaling pathway provides a framework that links many of the molecular changes that underpin the biological effects of boron intake.

Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Vitamin K and cancer

Subclinical vitamin K deficits refer to carboxylation defects of different types of vitamin K-dependent hepatic and extrahepatic so-called Gla proteins without prolongation of the prothrombin time. This condition has been reported in different clinical situations due to insufficient supply or malabsorption of vitamin K as well as drug interactions. This review discusses the effects of different vitamin K subspecies on tumour growth and the possible anti-tumour effects of increased vitamin K intake. Blocking carboxylation of vitamin K-dependent proteins with warfarin anticoagulation - what are the risks/benefits for carcinogenesis? Previous studies on both heparin and low molecular weight heparin blocking of the vitamin K-dependent factors X and II have shown tumour suppressive effects. Vitamin K has anti-inflammatory effects that could also impact carcinogenesis, but little data exists on this subject.

Dietary Protein Sources and Incidence of Breast Cancer: A Dose-Response Meta-Analysis of Prospective Studies

Protein is important to the human body, and different sources of protein may have different effects on the risk of breast cancer. Thus, we conducted a meta-analysis to investigate the association between different dietary protein sources and breast cancer risk. PubMed and several databases were searched until December 2015. Relevant articles were retrieved according to specific searching criteria. Forty-six prospective studies were included. The summary relative risk (RR) for highest versus lowest intake was 1.07 (95% confidence interval (CI) 1.01-1.14, I² = 34.6%) for processed meat, 0.92 (95% CI 0.84-1.00, I² = 0%) for soy food, 0.93 (95% CI 0.85-1.00, I² = 40.1%) for skim milk, and 0.90 (95% CI 0.82-1.00, I² = 0%) for yogurt. Similar conclusions were obtained in dose-response association for each serving increase: total red meat (RR: 1.07; 95% CI 1.01-1.14, I² = 7.1%), fresh red meat (RR: 1.13; 95% CI 1.01-1.26, I² = 56.4%), processed meat (RR: 1.09; 95% CI 1.02-1.17, I² = 11.8%), soy food (RR: 0.91; 95% CI 0.84-1.00, I² = 0%), and skim milk (RR: 0.96; 95% CI 0.92-1.00, I² = 11.9%). There was a null association between poultry, fish, egg, nuts, total milk, and whole milk intake and breast cancer risk. Higher total red meat, fresh red meat, and processed meat intake may be risk factors for breast cancer, whereas higher soy food and skim milk intake may reduce the risk of breast cancer.

The association of soy food consumption with the risk of subtype of breast cancers defined by hormone receptor and HER2 status

Soy food intake has previously been associated with reduced breast cancer risk. Epidemiological evidence for subgroups of breast cancer, particularly by menopausal and hormone receptor status, is less consistent. To evaluate the role of hormone receptor and menopausal status on the association between soy food intake and breast cancer risk, we measured usual soy food intake in adolescence and adulthood via food frequency questionnaire in 70,578 Chinese women, aged 40-70 years, recruited to the Shanghai Women's Health Study (1996-2000). After a median follow-up of 13.2 years (range: 0.01-15.0), 1,034 incident breast cancer cases were identified. Using Cox models, we found that adult soy intake was inversely associated with breast cancer risk [hazard ratio (HR) for fifth versus first quintile soy protein intake = 0.78; 95% confidence interval (CI):0.63-0.97]. The association was predominantly seen in premenopausal women (HR = 0.46; 95% CI:0.29-0.74). Analyses further stratified by hormone receptor status showed that adult soy intake was associated with significantly decreased risk of estrogen receptor (ER)+/progesterone receptor (PR)+ breast cancer in postmenopausal women (HR = 0.72; 95% CI:0.53-0.96) and decreased risk of ER-/PR- breast cancer in premenopausal women (HR = 0.46; 95% CI:0.22-0.97). The soy association did not vary by human epidermal growth factor-2 (HER2) status. Furthermore, we found that high soy intake during adulthood and adolescence was associated with reduced premenopausal breast cancer risk (HR = 0.53; 95% CI: 0.32-0.88; comparing third vs. first tertile) while high adulthood soy intake was associated with postmenopausal breast cancer only when adolescent intake was low (HR = 0.63; 95% CI: 0.43-0.91). Our study suggests that hormonal status, menopausal status and time window of exposure are important factors influencing the soy-breast cancer association.

Soy and Soy Products Intake, All-Cause Mortality, and Cause-Specific Mortality in Japan

Soy and soy products are popular ingredients in the Japanese diet. This study aimed to determine whether soy or soy products intake was associated with all-cause mortality in a community-based cohort in Japan. A total of 11 066 participants were obtained from an annual community-based health examination program. A self-administered questionnaire was used to collect information concerning soy and soy products intake and potential confounding factors. Associations between soy and soy products intake and all-cause mortality were assessed using hazard ratios (HRs). After adjusting for all factors, morality was significantly higher in men with infrequent soy intake (HR = 1.53; 95% confidence interval [CI] = 1.13-2.07) and with almost daily intake (HR = 1.55; 95% CI = 1.19-2.03) compared with intake 1 to 2 times per week. Cancer mortality was higher among men who reported rarely eating soy (HR = 1.74; 95% CI = 1.08-2.79). Soy products intake was not statistically significantly associated with all-cause mortality in both sexes.

Soy intake and breast cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population

OBJECTIVE

We reviewed epidemiological studies of soy intake and breast cancer among Japanese women. This report is one among a series of articles by our research group, which is evaluating the existing evidence concerning the association between health-related lifestyles and cancer.

METHODS

Original data were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database, complemented with manual searches. Evaluation of associations was based on the strength of evidence and the magnitude of association, together with biological plausibility.

RESULTS

Five cohort studies and six case-control studies were identified. Among the cohort studies, two studies observed that total soy intake (in terms of total amounts of soy foods or soy isoflavones) was associated with a moderate (0.5 ≤ relative risk ≤ 0.67 with statistical significance) or strong (relative risk ≤ 0.5 with statistical significance) risk reduction of breast cancer in postmenopausal women. Among the case-control studies, two studies reported a weak (0.67 ≤ odds ratio ≤ 1.5 with statistical significance or 0.5 ≤ odds ratio ≤ 0.67 without statistical significance) inverse association between total soy intake and the risk of breast cancer. In the former, this association was observed in all women combined-premenopausal and postmenopausal women-but in the latter, the association was confined to postmenopausal women. The associations of intakes of individual soy foods with the risk of breast cancer were generally null. There is some evidence that supports the biological plausibility of a protective effect of isoflavones on breast cancer risk.

CONCLUSIONS

We conclude that soy intake possibly decreases the risk of breast cancer among Japanese women.

Soy, red clover, and isoflavones and breast cancer: a systematic review

BACKGROUND

Soy and red clover isoflavones are controversial due to purported estrogenic activity and possible effects on breast cancer. We conducted a systematic review of soy and red clover for efficacy in improving menopausal symptoms in women with breast cancer, and for potential impact on risk of breast cancer incidence or recurrence.

METHODS

We searched MEDLINE, Embase, the Cochrane Library, and AMED from inception to March 2013 for human interventional or observational data pertaining to the safety and efficacy of soy and red clover isoflavones in patients with or at risk of breast cancer.

RESULTS

Of 4179 records, we included a total of 131 articles: 40 RCTs, 11 uncontrolled trials, and 80 observational studies. Five RCTs reported on the efficacy of soy for hot flashes, showing no significant reductions in hot flashes compared to placebo. There is lack of evidence showing harm from use of soy with respect to risk of breast cancer or recurrence, based on long term observational data. Soy intake consistent with that of a traditional Japanese diet (2-3 servings daily, containing 25-50mg isoflavones) may be protective against breast cancer and recurrence. Human trials show that soy does not increase circulating estradiol or affect estrogen-responsive target tissues. Prospective data of soy use in women taking tamoxifen does not indicate increased risk of recurrence. Evidence on red clover is limited, however existing studies suggest that it may not possess breast cancer-promoting effects.

CONCLUSION

Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (≥ 100 mg) isoflavones can be recommended for breast cancer patients.

Soy isoflavone intake and breast cancer risk in Japan: from the Takayama study

The effects of soy or isoflavone intake on breast cancer need to be examined further in epidemiologic studies. We assessed the associations of soy and isoflavone intake with breast cancer incidence in a population-based prospective cohort study in Japan. Participants were members from the Takayama study, aged 35 years or older in 1992. The follow-up was conducted from the time of the baseline study (September 1, 1992) to the end of March 2008. Cancer incidence was mainly confirmed through regional population-based cancer registries. Breast cancer was defined as code C50 according to ICD-10. Soy and isoflavone intakes were assessed with a validated food frequency questionnaire. Using the Cox proportional hazard models, the association of soy and isoflavone intake with breast cancer was assessed after adjustments for age, body mass index, physical activity, smoking, alcohol consumption, education, age at menarche, age at first delivery, menopausal status, number of children and history of hormone replacement therapy. Among the 15,607 women analyzed, 172 had developed breast cancer. The relative risks of postmenopausal breast cancer were lower among women with higher intakes of soy (trend p = 0.023) and isoflavone (trend p = 0.046), although the relative risks of premenopausal breast cancer were not associated with intakes of soy and isoflavone. Decreased risks of breast cancer were found even among women with a moderate intake of soy and isoflavone. These results suggested that soy and isoflavone intakes have a protective effect on postmenopausal breast cancer.

A simple food quality index predicts mortality in elderly Taiwanese

OBJECTIVES

To assess the relative predictive ability for mortality of the Overall Dietary Index-Revised (ODI-R) and the Dietary Diversity Score (DDS) among representative Taiwanese aged 65 and older.

DESIGN

Prospective cohort.

SETTING

The Elderly Nutrition and Health Survey in Taiwan during 1999-2000.

PARTICIPANTS

One thousand seven hundred forty three (860 men and 883 women).

MEASUREMENTS

Dietary quality measures, the ODI-R (0-100) and DDS (0-6) were based on 24-hour dietary recall and a food frequency questionnaire at baseline. Death by National Death Registry up to 2008 was the outcome measure.

RESULTS

During follow-up, 624 subjects died. The survivors had both significantly higher (P <0.001) ODI-R (66.9 vs. 63.6) and DDS (4.69 vs. 4.30) than the deceased. The two indices were correlated (r=0.46). After adjustment for potential covariates, the hazard ratios (HR) (95% CI) were 0.63 (0.42-0.97), 0.71 (0.49-1.04) and 0.53 (0.37-0.76) for those whose ODI-R scores were 60-65, 65-70, >70, respectively, compared to those whose ODI-R scores were > 50 (P for trend <0.001). For DDS, the multi-variable HRs (95% CI) were 0.74 (0.55-1.00), 0.52 (0.38-0.72) and 0.50 (0.31-0.81) for those whose DDS were 4, 5, 6, respectively, compared to those whose DDS were ≤3 (P for trend<0.001). Total cancer, diabetes mortalities and pneumonia were similarly benefited according to trends.

CONCLUSION

ODI-R ≥ 60, and DDS ≥ 4 are predictors of all-cause and cause-specific mortalities. Of the two, DDS is the more predictive. Nutrition policy could be informed and clinical practice enhanced by these population relevant food-health relationships.

Riscos e controvérsias na construção social do conceito de alimento saudável: o caso da soja

Riscos e controvérsias na construção social do conceito de alimento saudável são discutidos, tendo a soja como objeto de estudo. Estudos dos impactos da soja sobre a saúde e da sojicultura sobre o meio socioambiental foram revisados para analisar as controvérsias científicas da pesquisa na área de soja e saúde humana, bem como seu contexto político e as repercussões socioambientais da sojicultura. Com base na Sociologia do Conhecimento Científico e na Sociologia Ambiental, argumenta-se que a fronteira entre o alimento saudável e o de risco é tênue e vulnerável a diferentes influências construídas reflexivamente. Destaca-se a importância de ampliar o conceito de alimento saudável para o de alimentação saudável, considerando sua dimensão cultural e socioambiental.

The role of soy isoflavones in menopausal health: report of The North American Menopause Society/Wulf H. Utian Translational Science Symposium in Chicago, IL (October 2010)

OBJECTIVES

If and to what extent soy protein, soy isoflavones, and their metabolites, including S(--)-equol, have beneficial effects on women's health is currently unclear. The North American Menopause Society (NAMS)/Utian Translational Science Symposium on Soy and Soy Isoflavones convened October 9-10, 2010, to clarify basic and clinical research findings as they relate to the risk and benefits of soy products for peri- and postmenopausal women.

METHODS

A working group of faculty and panelists composed of clinical and research experts in the fields of women's health and botanicals met during a 2-day translational symposium to cover the latest evidence-based science on isoflavones as they affect menopausal symptoms, breast and endometrial cancer, atherosclerosis, bone loss, and cognition. Full descriptions of the bioavailability and pharmacokinetics of isoflavones were also presented. Subspecialty groups then broke off with the goal of translating the information into a report for general medical practice and identifying further research areas. All faculty and panelists reviewed the final report, which was then approved by the NAMS Board of Trustees.

RESULTS

From the hundreds of studies reviewed in this report, there are mixed results of the effects on midlife women. Soy-based isoflavones are modestly effective in relieving menopausal symptoms; supplements providing higher proportions of genistein or increased in S(--)-equol may provide more benefits. Soy food consumption is associated with lower risk of breast and endometrial cancer in observational studies. The efficacy of isoflavones on bone has not been proven, and the clinical picture of whether soy has cardiovascular benefits is still evolving. Preliminary findings on cognitive benefit from isoflavone therapy support a "critical window" hypothesis wherein younger postmenopausal women derive more than older women.

CONCLUSIONS

Several areas for further research have been identified on soy and midlife women. More clinical studies are needed that compare outcomes among women whose intestinal bacteria have the ability to convert daidzein to equol (equol producers) with those that lack that ability (equol nonproducers) in order to determine if equol producers derive greater benefits from soy supplementation. Larger studies are needed in younger postmenopausal women, and more research is needed to understand the modes of use of soy isoflavone supplements in women. The interrelations of other dietary components on soy isoflavones consumed as a part of diet or by supplement on equol production also require further study, as do potential interactions with prescription and over-the-counter medications. And finally, greater standardization and documentation of clinical trial data of soy are needed.

Soy product and isoflavone intake and breast cancer risk defined by hormone receptor status

The association between soy food consumption and breast cancer risk has been inconsistent. A hospital-based case-control study was conducted to assess the relationship between soy food intake and breast cancer risk according to the estrogen receptor (ER) and/or progesterone receptor (PR) status of breast cancer in Chinese women residing in Guangdong province from June 2007 to August 2008. A total of 438 consecutively recruited cases with primary breast cancer were frequency matched to 438 controls by age (5-year interval) and residence (rural/urban). Dietary intake was assessed by face-to-face interviews using a validated food frequency questionnaire. Odds ratios (OR) and 95% confidence intervals (CI) were obtained by using multiple unconditional logistic regression adjusted for the potential confounders. We observed a statistically significant inverse association between soy isoflavone and soy protein intake with breast cancer risk. The multivariate ORs (95% CIs) of breast cancer risk for the highest quartile compared with the lowest quartile were 0.54 (0.34-0.84) for soy isoflavone and 0.62 (0.40-0.96) for soy protein, respectively. A preventive effect of soy food was found for all subtypes of ER and/or PR status of breast cancer. The inverse association was more evident among premenopausal women. This study suggests that consumption of soy food, soy isoflavone, is inversely associated with the risk of breast cancer. The protective effects of soy did not seem to differ by ER and PR breast cancer status.

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.

Dietary intake of selected flavonols, flavones, and flavonoid-rich foods and risk of cancer in middle-aged and older women

BACKGROUND

Flavonoids may protect against cancer development through several biological mechanisms. However, epidemiologic studies on dietary flavonoids and cancer risk have yielded inconsistent results.

OBJECTIVE

We prospectively investigated the association between the intake of selected flavonoids and flavonoid-rich foods and risk of cancers in the Women's Health Study.

DESIGN

A total of 3234 incident cancer cases were identified during 11.5 y of follow-up among 38,408 women aged > or = 45 y. Intake of individual flavonols (quercetin, kaempferol, and myricetin) and flavones (apigenin and luteolin) was assessed from food-frequency questionnaires. Cox regression models were used to estimate the relative risk (RR) of total and site-specific cancer across increasing intakes of total and individual selected flavonoids and flavonoid-rich foods (tea, apple, broccoli, onion, and tofu).

RESULTS

The multivariate RRs of total cancer across increasing quintiles of total quantified flavonoid intake were 1.00, 1.00, 0.93, 0.94, and 0.97 (P for trend = 0.72). For site-specific cancers, the multivariate RRs in the highest quintile of total quantified flavonoid intake compared with the lowest quintile were 1.03 for breast cancer, 1.01 for colorectal cancer, 1.03 for lung cancer, 1.15 for endometrial cancer, and 1.09 for ovarian cancer (all P > 0.05). The associations for the individual flavonoid intakes were similar to those for the total intake. There was also no significant association between intake of flavonoid-rich foods and the incidence of total and site-specific cancers.

CONCLUSION

Our results do not support a major role of 5 common flavonols and flavones or selected flavonoid-rich foods in cancer prevention.

Effect of soybean on breast cancer according to receptor status: a case-control study in Japan

The possible association of high soy food consumption with low incidence of breast cancer in Asian countries has been widely investigated, but findings from epidemiologic studies have been inconsistent. Breast cancers defined by receptor status, estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) may have distinct etiologic factors. Here, we conducted a case-control study to clarify associations between intake of soybean products and breast cancer risk according to receptor status. A total of 678 breast cancer cases and 3,390 age- and menopausal status-matched noncancer controls were included. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using conditional logistic models adjusted for potential confounders. On analysis according to receptor status, we observed a significantly reduced risk of ER-positive (ER+) (top tertile OR = 0.74; 95% CI, 0.58-0.94; trend p = 0.01) and HER2-negative (HER2-) tumors (top tertile OR = 0.78; 95% CI, 0.61-0.99; trend p = 0.04). Further, when the 3 receptors were jointly examined, a reduced risk was observed only in patients with ER+/PR+/HER2- tumor (top tertile OR = 0.73; 95% CI, 0.54-0.97; trend p = 0.03). These findings indicate that the protective effect of soy against breast cancer risk differs by receptor status.

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.

Health effects of soy protein and isoflavones in humans

Epidemiological investigations suggest that soy consumption may be associated with a lower incidence of certain chronic diseases. Clinical studies also show that ingestion of soy proteins reduces the risk factors for cardiovascular disease. This led to the approval of the food-labeling health claim for soy proteins in the prevention of coronary heart disease by the U.S. FDA in 1999. Similar health petitions for soy proteins have also been approved thereafter in the United Kingdom, Brazil, South Africa, the Philippines, Indonesia, Korea, and Malaysia. However, the purported health benefits are quite variable in different studies. The Nutrition Committee of the American Heart Association has assessed 22 randomized trials conducted since 1999 and found that isolated soy protein with isoflavones (ISF) slightly decreased LDL cholesterol but had no effect on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. The other effects of soy consumption were not evident. Although the contributing factors to these discrepancies are not fully understood, the source of soybeans and processing procedures of the protein or ISF are believed to be important because of their effects on the content and intactness of certain bioactive protein subunits. Some studies have documented potential safety concerns on increased consumption of soy products. Impacts of soy products on thyroid and reproductive functions as well as on certain types of carcinogenesis require further study in this context. Overall, existing data are inconsistent or inadequate in supporting most of the suggested health benefits of consuming soy protein or ISF.

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.

Epidemiology of soy exposures and breast cancer risk

Most of the early studies published on soy and breast cancer were not designed to test the effect of soy; the assessment of soy intake was usually crude and few potential confounders were considered in the analysis. In this review, we focused on studies with relatively complete assessment of dietary soy exposure in the targeted populations and appropriate consideration for potential confounders in the statistical analysis of study data. Meta-analysis of the 8 (1 cohort, 7 case-control) studies conducted in high-soy-consuming Asians show a significant trend of decreasing risk with increasing soy food intake. Compared to the lowest level of soy food intake (<or=5 mg isoflavones per day), risk was intermediate (OR=0.88, 95% confidence interval (CI)=0.78-0.98) among those with modest ( approximately 10 mg isoflavones per day) intake and lowest (OR=0.71, 95% CI=0.60-0.85) among those with high intake (>or=20 mg isoflavones per day). In contrast, soy intake was unrelated to breast cancer risk in studies conducted in the 11 low-soy-consuming Western populations whose average highest and lowest soy isoflavone intake levels were around 0.8 and 0.15 mg per day, respectively. Thus, the evidence to date, based largely on case-control studies, suggest that soy food intake in the amount consumed in Asian populations may have protective effects against breast cancer.

Comparisons of food intake between breast cancer patients and controls in Korean women

The purpose of this study was to compare food intakes between Korean breast cancer patients and a healthy control group. We compared the intake of nutrients of 117 food items between Korean breast cancer patients (n=97) and age matched healthy controls (n=97). Nutrient intake was estimated using a quantitative food frequency questionnaire. The mean caloric intake of breast cancer patients and healthy controls was not significantly different. Breast cancer patients consumed significantly less fat and antioxidant nutrients such as vitamin A, retinol, beta-carotene, vitamin C and vitamin E when compared to the control subjects. Among the food items, the intake of eggs (p<0.01), legumes (p<0.05), vegetables (p<0.05), seasonings (p<0.001), and oils and fats (p<0.01) in breast cancer patients was significantly lower than that in the controls. These results suggest that Korean breast cancer patients consumed less amount of soy and vegetables, which are rich source of antioxidant nutrients and phytosterols. Thus, dietary guidance to increase intake of these foods may be beneficial in the prevention of breast cancer.