Phytoestrogen Concentrations in Serum and Spot Urine as Biomarkers for Dietary Phytoestrogen Intake and Their Relation to Breast Cancer Risk in European Prospective Investigation of Cancer and Nutrition-Norfolk

Equol: a metabolite of gut microbiota with potential antitumor effects

An increasing number of studies have shown that the consumption of soybeans and soybeans products is beneficial to human health, and the biological activity of soy products may be attributed to the presence of Soy Isoflavones (SI) in soybeans. In the intestinal tracts of humans and animals, certain specific bacteria can metabolize soy isoflavones into equol. Equol has a similar chemical structure to endogenous estradiol in the human body, which can bind with estrogen receptors and exert weak estrogen effects. Therefore, equol plays an important role in the occurrence and development of a variety of hormone-dependent malignancies such as breast cancer and prostate cancer. Despite the numerous health benefits of equol for humans, only 30-50% of the population can metabolize soy isoflavones into equol, with individual variation in gut microbiota being the main reason. This article provides an overview of the relevant gut microbiota involved in the synthesis of equol and its anti-tumor effects in various types of cancer. It also summarizes the molecular mechanisms underlying its anti-tumor properties, aiming to provide a more reliable theoretical basis for the rational utilization of equol in the field of cancer treatment.

Phytosterols activating nuclear receptors are involving in steroid hormone-dependent cancers: Myth or fact?

Nuclear receptors (NRs) represent intracellular proteins that function as a signaling network of transcriptional factors to control genes in response to a variety of environmental, dietary, and hormonal stimulations or serve as orphan receptors lacking a recognized ligand. They also play an essential role in normal development, metabolism, cell growth, cell division, physiology, reproduction, and homeostasis and function as biological markers for tumor subclassification and as targets for hormone therapy. NRs, including steroid hormone receptors (SHRs), have been studied as tools to examine the fundamentals of transcriptional regulation within the development of mammals and human physiology, in addition to their links to disturbances. In this regard, it is widely recognized that aberrant NR signaling is responsible for the pathological growth of hormone-dependent tumors in response to SHRs dysregulation and consequently represents a potential therapeutic candidate in a range of diseases, as in the case of prostate cancer and breast cancer. On the other hand, phytosterols are a group of plant-derived compounds that act directly as ligands for NRs and have proven their efficacy in the management of diabetes, heart diseases, and cancers. However, these plants are not suggested in cases of hormone-dependent cancer since a certain group of plants contains molecules with a chemical structure similar to that of estrogens, which are known as phytoestrogens or estrogen-like compounds, such as lignans, coumestans, and isoflavones. Therefore, it remains an open and controversial debate regarding whether consuming a phytosterol-rich diet and adopting a vegetarian lifestyle like the Mediterranean diet may increase the risk of developing steroid hormone-dependent cancers by constitutively activating SHRs and thereby leading to tumor transformation. Overall, the purpose of this review is to better understand the relevant mechanistic pathways and explore epidemiological investigations in order to establish that phytosterols may contribute to the activation of NRs as cancer drivers in hormone-dependent cancers.

Next generation risk assessment of human exposure to estrogens using safe comparator compound values based on in vitro bioactivity assays

In next generation risk assessment (NGRA), the Dietary Comparator Ratio (DCR) can be used to assess the safety of chemical exposures to humans in a 3R compliant approach. The DCR compares the Exposure Activity Ratio (EAR) for exposure to a compound of interest (EARtest) to the EAR for an established safe exposure level to a comparator compound (EARcomparator), acting by the same mode of action. It can be concluded that the exposure to a test compound is safe at a corresponding DCR ≤ 1. In this study, genistein (GEN) was selected as a comparator compound by comparison of reported safe internal exposures to GEN to its BMCL05, as no effect level, the latter determined in the in vitro estrogenic MCF7/Bos proliferation, T47D ER-CALUX, and U2OS ERα-CALUX assay. The EARcomparator was defined using the BMCL05 and EC50 values from the 3 in vitro assays and subsequently used to calculate the DCRs for exposures to 14 test compounds, predicting the (absence of) estrogenicity. The predictions were evaluated by comparison to reported in vivo estrogenicity in humans for these exposures. The results obtained support in the DCR approach as an important animal-free new approach methodology (NAM) in NGRA and show how in vitro assays can be used to define DCR values.

Validation of ELISAs for Isoflavones and Enterolactone for Phytoestrogen Intake Assessment in the French Population

Phytoestrogens are dietary compounds with low estrogenic activity. The two main categories in the French diet are isoflavones from pulses and enterolignans metabolized by the gut flora from various lignans found in fruits, vegetables, grains, and beverages. Isoflavones and lignans have different effects on human physiology and can antagonize each other. Comprehensive lists of phytoestrogen sources were constructed based on measurements and literature data. The 24 h and 48 h dietary recalls were proposed to the volunteers of the ISOLED cohort (NCT03421184). Urine and plasma samples from these volunteers were assayed for genistein, daidzein, equol, and enterolactone. A dietary score was constructed considering the pharmacokinetic characteristics of these compounds. Correlation analyses were applied to fluid concentrations associated with dietary scores. Pearson correlations reached 0.921 (p < 0.001) for urine_IF, 0.900 (p < 0.001) for plasma_IF, 0.764 (p < 0.001) for urine_ENL, and 0.723 (p < 0.001) for plasma_ENL. ELISAs associated with careful intake assessments proved to be good tools for phytoestrogens' exposure estimation.

Health Effects of Soy Isoflavones and Green Tea Catechins on Cancer and Cardiovascular Diseases Based on Urinary Biomarker Levels

Plant polyphenols have various health effects. Genistein, which is abundant in soybeans, and epigallocatechin-3-gallate, which is abundant in green tea, are major flavonoids, a subclass group of polyphenols. Several epidemiological studies have shown that these flavonoids have beneficial effects against cancer and cardiovascular diseases. However, other studies did not show such effects. Several confounding factors, including recall bias, are related to these inconsistent findings, and the determination of metabolites in the urine may be useful in reducing the number of confounding factors. Equipment, which can be used by research participants to collect samples from a portion of voided urine within 24 h without the help of medical workers, has been developed for epidemiological investigations. Previous studies, in which flavonoid metabolites in these urine samples were measured, revealed that soy intake was correlated with a reduced risk of certain types of cancer and cardiovascular diseases worldwide. Although soybeans and green tea consumption may have protective effects against cancer and cardiovascular diseases, further clinical studies that consider different confounding factors are required to provide evidence for the actual impact of dietary flavonoids on human diseases, including cancer and cardiovascular diseases. One possible mechanism involved is discussed in relation to the downregulation of reactive oxygen species and the upregulation of 5'-adenosine monophosphate-activated protein kinase elicited by these flavonoids.

Development of an Assay for Soy Isoflavones in Women's Hair

Soy isoflavones, at adequate dosages, have estrogenic and anti-thyroidal effects in animals and humans, which can either be beneficial or adverse, depending on the consumer’s physiological status. Hence, this study presents an assay of soy isoflavones in hair, aiming to give new information about a person’s exposure to isoflavones, when health issues related to estrogenic or thyroidal effects are observed. Aqueous or organic extraction procedures following acidic, basic, or enzymatic digestions were tested on 60 hair samples (from volunteers) from a hairdresser, and a clinical trial 2017T2-29. The acidic digestion method was the most efficient regarding isoflavones. A specific inquiry was developed to assess the dietary habits of French consumers based on the analysis of 12,707 food labels from France. It was used to check for the reliability of the new assay method. A score for the consumer exposures to isoflavones was built considering, among other parameters, soy-based diets and foodstuff containing soy as an ingredient, i.e., “hidden-soy”. The correlation between this score and isoflavone measurements in hair reached 0.947; p < 0.001. Therefore, providing that relevant data are considered to assess isoflavone exposure, hair that smoothens daily isoflavone intake variations, is a relevant tissue to assess human isoflavone exposure for subsequent health analyses.

Urinary Phytoestrogen Levels Are Associated with Female Hormonal Cancers: An Analysis of NHANES Data From 1999 to 2010

Phytoestrogens are plant-derived compounds that are structurally similar to endogenous estrogens. Studies have shown phytoestrogens to have possible health benefits although they could also act as endocrine disruptors. This is particularly relevant for estrogen-dependent cancers since estrogens increase risk of breast, endometrial, and ovarian cancer. Using data from the National Health and Nutritional Examination Survey (NHANES), we assessed the associations between urinary phytoestrogens (daidzein, equol, o-Desmethylangolensin (O-DMA), genistein, enterodiol, enterolactone) and breast, endometrial, and ovarian cancer using multivariate logistic regression with odds ratios (ORs) and 95% confidence intervals (CIs). Cancer diagnosis and other characteristics were collected via in-person questionnaires. We found women in the highest tertile for daidzein and enterodiol had over twice the odds of having breast cancer (OR = 2.51, 95% CI 1.44-4.36 for daidzein, OR = 2.78, 95% CI 1.44-5.37 for enterodiol). In addition, women in the highest tertiles for daidzein and genistein had three to four times the odds of having endometrial cancer, respectively (OR = 3.09, 95% CI 1.01-9.49 for daidzein, OR = 4.00, 95% CI 1.38-11.59 for genistein). Overall, phytoestrogens were positively associated with breast and endometrial cancer although the associations varied by phytoestrogen type. Additional studies are needed to further inform phytoestrogens' role in disease etiology.Supplemental data for this article is available online at at https://doi.org/10.1080/01635581.2021.2020304.

Associations of maternal soy product consumption and urinary isoflavone concentrations with neonatal anthropometry: A prospective cohort study

Isoflavones (ISOs) are naturally occurring endocrine-disrupting compounds. Few human studies have evaluated the effects of ISO exposure on neonatal anthropometry. This study aimed to examine the associations of maternal soy product consumption and urinary ISO concentrations, including genistein, daidzein, glycitein, and equol, with neonatal anthropometry, based on a Chinese cohort study. In Shanghai-Minhang Birth Cohort Study, pregnant women at 12-16 weeks of gestation were recruited, and they completed a structured questionnaire to assess soy product consumption during pregnancy. They also provided a single spot urine sample for the ISO assay. Neonatal anthropometric indices (birth weight; arm, waist, and head circumference; and triceps, back, and abdominal skinfold thickness) were measured at birth. Multivariable linear regression analysis was performed among the 1188 mother-infant pairs to examine the associations between maternal soy product consumption and neonatal anthropometry. The same statistical model was applied to examine the associations between maternal ISO exposure and neonatal anthropometry among 480 mother-infant pairs. Neonate girls born to mothers who "sometimes" and "frequent" consumed soy products had 169.1 g (95% confidence interval [CI], -68.9-407.1) and 256.5 g (95% CI, 17.1-495.8) higher birth weight, respectively, than those born to mothers who "never" consumed soy products during pregnancy. We observed consistent associations between higher maternal urine ISO concentrations and increased anthropometric indices (birth weight, arm and waist circumference, and triceps and abdominal skinfold thickness) in neonate girls, while no association was observed among boys. The findings suggested that maternal dietary ISO intake during pregnancy is associated with fetal development in a sex-specific pattern. In addition, follow-up studies are required to evaluate whether the observed changes in anthropometric indices at birth are associated with health conditions later in life.

Neither soyfoods nor isoflavones warrant classification as endocrine disruptors: a technical review of the observational and clinical data

Soybeans are a rich source of isoflavones, which are classified as phytoestrogens. Despite numerous proposed benefits, isoflavones are often classified as endocrine disruptors, based primarily on animal studies. However, there are ample human data regarding the health effects of isoflavones. We conducted a technical review, systematically searching Medline, EMBASE, and the Cochrane Library (from inception through January 2021). We included clinical studies, observational studies, and systematic reviews and meta-analyses (SRMA) that examined the relationship between soy and/or isoflavone intake and endocrine-related endpoints. 417 reports (229 observational studies, 157 clinical studies and 32 SRMAs) met our eligibility criteria. The available evidence indicates that isoflavone intake does not adversely affect thyroid function. Adverse effects are also not seen on breast or endometrial tissue or estrogen levels in women, or testosterone or estrogen levels, or sperm or semen parameters in men. Although menstrual cycle length may be slightly increased, ovulation is not prevented. Limited insight could be gained about possible impacts of in utero isoflavone exposure, but the existing data are reassuring. Adverse effects of isoflavone intake were not identified in children, but limited research has been conducted. After extensive review, the evidence does not support classifying isoflavones as endocrine disruptors.

Metabolomic and Transcriptomic Analysis of MCF-7 Cells Exposed to 23 Chemicals at Human-Relevant Levels: Estimation of Individual Chemical Contribution to Effects

BACKGROUND

Humans are constantly being exposed to various xenobiotics at relatively low concentrations. To date, limited evidence is available to ascertain whether a complex xenobiotic mixture at human-relevant levels causes any health effect. Moreover, there is no effective method to pinpoint the contribution of each chemical toward such an effect.

OBJECTIVES

This study aims to understand the responses of cells to a mixture containing 23 xenobiotics at human-relevant levels and develop a feasible method to decipher the chemical(s) that contribute significantly to the observed effect.

METHODS

We characterized the metabolome and transcriptome of breast cancer cells (MCF-7) before and after exposure to the mixture at human-relevant levels; preexposure levels were derived from existing large-scale biomonitoring data. A high-throughput metabolomics-based "leave-one-out" method was proposed to understand the relative contribution of each component by comparing the metabolome with and without the particular chemical in the mixture.

RESULTS

The metabolomic analysis suggested that the mixture altered metabolites associated with cell proliferation and oxidative stress. For the transcriptomes, gene ontology terms and pathways including "cell cycle," "cell proliferation," and "cell division" were significantly altered after mixture exposure. The mixture altered genes associated with pathways such as "genotoxicity" and "nuclear factor erythroid 2-related factor 2 (Nrf2)." Through joint pathways analysis, metabolites and genes were observed to be well-aligned in pyrimidine and purine metabolisms. The leave-one-out results showed that many chemicals made their contributions to specific metabolic pathways. The overall metabolome pattern of the absence of 2,4-dihyroxybenzophenone (DHB) or bisphenol A (BPA) showed great resemblance to controls, suggesting their higher relative contribution to the observed effect.

DISCUSSION

The omics results showed that exposure to the mixture at human-relevant levels can induce significant in vitro cellular changes. Also, the leave one out method offers an effective approach for deconvoluting the effects of the mixture. https://doi.org/10.1289/EHP6641.

Detection of Phytoestrogen Metabolites in Breastfed Infants' Urine and the Corresponding Breast Milk by Liquid Chromatography-Tandem Mass Spectrometry

To date, there has been limited information on phytoestrogen (PE) exposure and metabolism in breastfed infants. In the present work, 50 sample pairs of Chinese breastfed infants' urine and the corresponding breast milk were collected. The contents of the relevant PE metabolites in the biosamples were detected via liquid chromatography-tandem mass spectrometry. The correlations between the PE metabolite contents in breastfed infants' urine and those in the corresponding breast milk were analyzed. The average concentrations of total PE metabolites in breast milk and urine were 0.27 and 0.23 nmol/mL, respectively. Genistein and enterolactone levels in the infant urine were positively correlated with their concentrations in the corresponding breast milk samples, which implies that urine excretion can be utilized as a noninvasive parameter for precise genistein and enterolactone intake assessment. Additionally, the efficiency of PE urine excretion showed significant differences across infants with different ages, genders, and durations of pregnancy.

Equol: A Bacterial Metabolite from The Daidzein Isoflavone and Its Presumed Beneficial Health Effects

Epidemiological data suggest that regular intake of isoflavones from soy reduces the incidence of estrogen-dependent and aging-associated disorders, such as menopause symptoms in women, osteoporosis, cardiovascular diseases and cancer. Equol, produced from daidzein, is the isoflavone-derived metabolite with the greatest estrogenic and antioxidant activity. Consequently, equol has been endorsed as having many beneficial effects on human health. The conversion of daidzein into equol takes place in the intestine via the action of reductase enzymes belonging to incompletely characterized members of the gut microbiota. While all animal species analyzed so far produce equol, only between one third and one half of human subjects (depending on the community) are able to do so, ostensibly those that harbor equol-producing microbes. Conceivably, these subjects might be the only ones who can fully benefit from soy or isoflavone consumption. This review summarizes current knowledge on the microorganisms involved in, the genetic background to, and the biochemical pathways of, equol biosynthesis. It also outlines the results of recent clinical trials and meta-analyses on the effects of equol on different areas of human health and discusses briefly its presumptive mode of action.

Gender Differences in Phytoestrogens and the Relationship with Speed of Processing in Older Adults: A Cross-Sectional Analysis of NHANES, 1999-2002

Sex hormone changes in adults are known to play a part in aging, including cognitive aging. Dietary intake of phytoestrogens can mimic estrogenic effects on brain function. Since sex hormones differ between genders, it is important to examine gender differences in the phytoestrogen–cognition association. Therefore, the goal of this study is to examine the relationship between urinary phytoestrogens and speed of processing (SOP) and the variation of the association between genders in older adults. Participants were drawn from the 1999–2002 National Health and Nutrition Examination Survey and included 354 individuals aged 65–85 years old. General linear models (GLMs) were used to test for significant gender differences in the relationship between phytoestrogens and SOP. Results from the GLMs showed significant gender differences in the relationship between genistein and SOP. Higher levels of genistein were associated with better SOP in women. This relationship was reversed in men: higher genistein levels were associated with worse performance. Results indicate that there are distinct gender differences in the relationship between genistein and SOP. These results emphasize the importance of considering gender differences when devising dietary and pharmacologic interventions that target phytoestrogens to improve brain health.

The Advent of Salivary Breast Cancer Biomarker Detection Using Affinity Sensors

Breast Cancer is one of the world's most notorious diseases affecting two million women in 2018 worldwide. It is a highly heterogeneous disease, making it difficult to treat. However, its linear progression makes it a candidate for early screening programs, and the earlier its detection the higher the chance of recovery. However, one key hurdle for breast cancer screening is the fact that most screening techniques are expensive, time-consuming, and cumbersome, making them impractical for use in several parts of the world. One current trend in breast cancer detection has pointed to a possible solution, the use of salivary breast cancer biomarkers. Saliva is an attractive medium for diagnosis because it is readily available in large quantities, easy to obtain at low cost, and contains all the biomarkers present in blood, albeit in lower quantities. Affinity sensors are devices that detect molecules through their interactions with biological recognition molecules. Their low cost, high sensitivity, and selectivity, as well as rapid detection time make them an attractive alternative to traditional means of detection. In this review article, we discuss the current status of breast cancer diagnosis, its salivary biomarkers, as well as the current trends in the development of affinity sensors for their detection.

Factors Explaining Interpersonal Variation in Plasma Enterolactone Concentrations in Humans

Lignans are diphenolic plant compounds with potential health modulating properties that are absorbed to the circulation and metabolized to the enterolignans enterodiol (END) and enterolactone (ENL) by gut microbiota. Epidemiological studies have inconsistently shown that a high lignan intake and circulating ENL are associated with reduced risk of breast‐, prostate‐, and colorectal cancer as well as cardiovascular disease and total and cause‐specific mortality. Inconsistencies can be due to interpersonal variation of ENL formation or responses. The aim of this review is to identify and evaluate the impact of factors influencing variability in plasma concentrations of the main enterolignan, ENL. The main determinants of plasma ENL concentrations are intake of lignan and lignan‐rich foods, composition and activity of intestinal microflora, antimicrobial use, nutrient intake, BMI, smoking, sex, and age. Composition and activity of the intestinal microbiota appear to be the most critical factor governing interpersonal variability in plasma ENL concentration followed by the use of antibiotics. Future studies with combined data from gut microbiota and metabolomics with food intake and life style data can be used to estimate the relative contribution of the different factors to ENL concentration in quantitative terms.

Serum Concentration of Genistein, Luteolin and Colorectal Cancer Prognosis

Although flavonoid phytoestrogens have been suggested to be associated with reduced risk of colorectal cancer (CRC), their influence on CRC prognosis remains uncertain. A population-based cohort of 2051 patients diagnosed with stage I⁻III CRC in southwest Germany in 2003⁻2010 were followed for five years. Post-diagnostic serum concentration of genistein and luteolin were measured using Ultra-Performance Liquid Chromatography with mass spectrometry. Multivariable Cox regression analysis was conducted to calculate the Hazard Ratios (HRs) and 95% confidence interval (CI) for the association between flavonoids concentration and overall morality, CRC-specific mortality, CRC recurrence, and disease-free survival (DFS). Median (interquartile range) serum concentration of genistein and luteolin was 11.90 ng/µL (10.08⁻14.13) and 7.20 ng/µL (6.40⁻8.16), respectively. Neither serum genistein nor luteolin was associated with CRC prognosis. There was no clear evidence of departure from linearity. However, the association might be differential by adjuvant chemotherapy. Associations pointed towards lower risk in patients who received chemotherapy and higher risk in those without chemotherapy for overall mortality regarding serum genistein (P-interaction = 0.02) and correspondingly for CRC recurrence (P-interaction: 0.03) and DFS (P-interaction: 0.01) with respect to luteolin. Our study provides little evidence that serum genistein and luteolin are associated with colorectal cancer prognosis. Future studies are warranted to evaluate the potential interaction with adjuvant chemotherapy.

The association between urinary genistein levels and mortality among adults in the United States

Background

Current research on the relationship between phytoestrogens and mortality has been inconclusive. We explored the relationship between genistein, a phytoestrogen, and mortality in a large cohort representative of the United States population.

Methods

Data were analyzed from the National Health and Nutrition Examination Survey (NHANES) from 1999–2010. Normalized urinary genistein (nUG) was analyzed as a log-transformed continuous variable and in quartiles. Mortality data were obtained from the National Death Index and matched to the NHANES participants. Survival analyses were conducted using the Kaplan-Meier analysis. Cox proportional hazard models were constructed for all-cause and cause-specific mortality without and with adjustment for potential confounding variables.

Results

Of 11,497 participants, 944 died during the 64,443 person-years follow-up. The all-cause mortality rate was significantly lower in the lowest quartile compared to the highest quartile (incidence rate ratio = 2.14, 95%CI = 1.76 to 2.60). Compared to the lowest quartile, the highest quartile had significantly higher adjusted all-cause (HR = 1.57, 95%CI = 1.23 to 2.00), cardiovascular (HR = 1.67, 95%CI = 1.04 to 2.68), and other-cause (HR = 1.85, 95%CI = 1.33 to 2.57) mortality.

Conclusion

We found that high urinary genistein levels were associated with increased risk of all-cause, cardiovascular, and other-cause mortality. This is contrary to popular opinion on the health benefits of genistein and needs further research.

Effect of S-equol and Soy Isoflavones on Heart and Brain

BACKGROUND

Observational studies in Asia show that dietary intake of soy isoflavones had a significant inverse association with coronary heart disease (CHD). A recent randomized controlled trial (RCT) of soy isoflavones on atherosclerosis in the US, however, failed to show their benefit. The discrepancy may be due to the much lower prevalence of S-equol producers in Westerners: Only 20-30% of Westerners produce S-equol in contrast to 50-70% in Asians. S-equol is a metabolite of dietary soy isoflavone daidzein by gut microbiome and possesses the most antiatherogenic properties among all isoflavones. Several short-duration RCTs documented that soy isoflavones improves arterial stiffness. Accumulating evidence shows that both atherosclerosis and arterial stiffness are positively associated with cognitive decline/dementia. Therefore, potentially, soy isoflavones, especially S-equol, are protective against cognitive decline/dementia.

METHODS/RESULTS

This narrative review of clinical and epidemiological studies provides an overview of the health benefits of soy isoflavones and introduces S-equol. Second, we review recent evidence on the association of soy isoflavones and S-equol with CHD, atherosclerosis, and arterial stiffness as well as the association of atherosclerosis and arterial stiffness with cognitive decline/ dementia. Third, we highlight recent studies that report the association of soy isoflavones and S-equol with cognitive decline/dementia. Lastly, we discuss the future directions of clinical and epidemiological research on the relationship of S-equol and CHD and dementia.

CONCLUSIONS

Evidence from observational studies and short-term RCTs suggests that S-equol is anti-atherogenic and improves arterial stiffness and may prevent CHD and cognitive impairment/ dementia. Well-designed long-term (≥ 2years) RCTs should be pursued.

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.

Baseline Urinary Phytoestrogen Levels and the Natural History of Untreated, Localised Prostate Cancer in a British Population

Aim

To determine whether urinary concentrations of phytoestrogens are associated with the rate of disease progression in men with untreated, localised prostate cancer.

Patients and methods

Patients with untreated, localised prostatic adenocarcinoma on a prospective clinical study of active surveillance had urine samples collected at baseline. Patients underwent monitoring with serial PSA levels and repeat octant prostate biopsies. Disease progression was defined as either adverse histology on repeat biopsy (primary Gleason grade ≥4, or >50% positive cores) or radical treatment for PSA velocity >1 ng/mL/year. Time to disease progression was analysed with respect to baseline urinary levels of genistein, enterolactone, daidzein and equol, assayed using liquid chromatography/tandem mass spectrometry.

Results

191 patients were evaluable, with a median follow-up of 2.5 years. 71 patients experienced disease progression. No significant association was seen between time to disease progression and baseline urinary levels of daidzein (p=0.85), genistein (p=0.81), enterolactone (p=0.085) or equol (p=0.33). No significant association was seen between adverse histology on repeat biopsy and urinary levels of either daidzein (p=0.85), genistein (p=0.58), enterolactone (p=0.88) or equol (p=0.71). There was no significant correlation between PSA velocity and urinary levels of daidzein (p=0.90), genistein (p=0.98), enterolactone (p=0.10) or equol (p=0.60).

Conclusion

These data do not support the hypothesis that phytoestrogens prevent disease progression in men with localised prostate cancer.

Phytoestrogen Concentrations in Human Urine as Biomarkers for Dietary Phytoestrogen Intake in Mexican Women

There has been substantial interest in phytoestrogens, because of their potential effect in reducing cancer and heart disease risk. Measuring concentrations of phytoestrogens in urine is an alternative method for conducting epidemiological studies. Our objective was to evaluate the urinary excretion of phytoestrogens as biomarkers for dietary phytoestrogen intake in Mexican women. Participants were 100 healthy women from 25 to 80 years of age. A food frequency questionnaire (FFQ) and a 24 h recall were used to estimate habitual and recent intakes of isoflavones, lignans, flavonols, coumestrol, resveratrol, naringenin, and luteolin. Urinary concentrations were measured by liquid chromatography (HPLC) coupled to mass spectrometry (MS) using the electrospray ionization interface (ESI) and diode array detector (DAD) (HPLC-DAD-ESI-MS). Spearman correlation coefficients were used to evaluate associations between dietary intake and urine concentrations. The habitual consumption (FFQ) of total phytoestrogens was 37.56 mg/day. In urine, the higher compounds were naringenin (60.1 µg/L) and enterolactone (41.7 µg/L). Recent intakes (24 h recall) of isoflavones (r = 0.460, p < 0.001), lignans (r = 0.550, p < 0.0001), flavonoids (r = 0.240, p < 0.05), and total phytoestrogens (r = 0.410, p < 0.001) were correlated to their urinary levels. Total phytoestrogen intakes estimated by the FFQ showed higher correlations to urinary levels (r = 0.730, p < 0.0001). Urinary phytoestrogens may be useful as biomarkers of phytoestrogen intake, and as a tool for evaluating the relationship of intake and disease risk in Mexican women.

Association between Dietary Share of Ultra-Processed Foods and Urinary Concentrations of Phytoestrogens in the US

The aim of this study was to examine the relationship between dietary contribution of ultra-processed foods and urinary phytoestrogen concentrations in the US. Participants from cross-sectional 2009-2010 National Health and Nutrition Examination Survey aged 6+ years, selected to measure urinary phytoestrogens and with one 24-h dietary recall were evaluated (2692 participants). Food items were classified according to NOVA (a name, not an acronym), a four-group food classification based on the extent and purpose of industrial food processing. Ultra-processed foods are formulations manufactured using several ingredients and a series of processes (hence "ultra-processed"). Most of their ingredients are lower-cost industrial sources of dietary energy and nutrients, with additives used for the purpose of imitating sensorial qualities of minimally processed foods or of culinary preparations of these foods. Studied phytoestrogens included lignans (enterolactone and enterodiol) and isoflavones (genistein, daidzein, O-desmethylangolensin and equol). Gaussian regression was used to compare average urinary phytoestrogen concentrations (normalized by creatinine) across quintiles of energy share of ultra-processed foods. Models incorporated survey sample weights and were adjusted for age, sex, race/ethnicity, family income, and education, among other factors. Adjusted enterodiol geometric means decreased monotonically from 60.6 in the lowest quintile to 35.1 µg/g creatinine in the highest, while adjusted enterolactone geometric means dropped from 281.1 to 200.1 across the same quintiles, respectively. No significant linear trend was observed in the association between these quintiles and isoflavone concentrations. This finding reinforces the existing evidence regarding the negative impact of ultra-processed food consumption on the overall quality of the diet and expands it to include non-nutrients such as lignans.

Plasma equol concentration is not associated with breast cancer and fibrocystic breast conditions among women in Shanghai, China

Equol (a bacterial metabolite of the soy isoflavone daidzein) is produced by 30% to 50% of humans and may be associated with health outcomes. We hypothesized that plasma equol would be inversely associated with risks of fibrocystic breast conditions (FBC) and breast cancer (BC). Plasma from women in a breast self-examination trial in Shanghai with BC (n=269) or FBC (n=443), and age-matched controls (n=1027) was analyzed for isoflavones. Equol was grouped into categories (<20, 20-<45, and ≥45nmol/L) and, among women with daidzein ≥20nmol/L, the log10 equol:daidzein ratio was grouped into tertiles. Where available, non-cancerous tissue (NCT) adjacent to the carcinomas from women with BC were classified as non-proliferative or proliferative (n=130 and 172, respectively). The lesions from women with FBC were similarly classified (n=99 and 92, respectively). Odds ratios (OR) and 95% confidence intervals (CI) were calculated across equol categories and tertiles of log10 equol:daidzein ratio. Equol categories were not associated with FBC or BC (P>.05). For log10 equol:daidzein, compared to controls there were positive associations in the mid tertile for proliferative FBC (OR 2.06, 95% CI 1.08-3.93), BC with proliferative NCT (OR 2.95, 95% CI 1.37-6.35), and all BC regardless of histology (OR 2.37, 95% CI 1.43-3.95). However, trends in ORs with increasing plasma equol values or equol:daidzein ratios were not observed (P>.05). The results of this study do not provide evidence that equol plays a role in the etiology of these breast conditions. However, further work is needed to confirm or refute this conclusion.

Urinary isoflavone phytoestrogens in German children and adolescents--a longitudinal examination in the DONALD cohort

SCOPE

In light of concerns about hormonally active agents, it is important to assess human exposure to such compounds, especially in children as a susceptible subgroup. Estrogenic plant constituents are present in the human diet in varying levels, in particular the isoflavones daidzein (DAI) and genistein (GEN). We aimed to examine age-dependent and secular trends in phytoestrogen exposures and to investigate equol (EQ) excretion of German children using biomarker analysis in 24-h urine samples from a longitudinally designed study.

METHODS AND RESULTS

The concentrations of DAI, its metabolite EQ and GEN were determined by GC-MS analysis in 24-h urines (510 samples) collected between 1985 and 2000 in 90 (47 boys) German children (6-18 years old), who are participants in the Dortmund Nutritional and Anthropometric Longitudinally Designed study. The results from the urinary biomarker analysis indicate isoflavone exposures at quite variable levels in German children: Analyte concentrations in over 500 urine samples cover the range reported previously in adults on typical German diet and with soy intake. EQ, the DAI metabolite produced by the gastrointestinal microflora, was detected in a high fraction of all samples, with 28/90 children (31%) excreting EQ in all their urines, and 62/90 children (68%) in at least one sample. Interestingly, when multiple urines obtained from individuals at different ages (6-18 years) were analyzed, EQ formation did not appear to be a constant trait over time. When stratified by sex, DAI, EQ and GEN concentrations (ng/mL) in urines and excretion rates (μg/day) were similar in boys and girls. Total isoflavone excretion rates (μg/day) increased during childhood (6-12 years) (p=0.02) and were constant during adolescence (13-18 years) (p=0.6). No clear trend for changes in dietary isoflavone exposure over the total study period was seen (p=0.7).

CONCLUSIONS

In conclusion, biomarkers in urine of German children and adolescents indicate a frequent, but widely variable dietary isoflavone intake and suggest no secular increase (1985-2000) in the exposure to isoflavone phytoestrogens among German children and adolescents.

Profiles of phytoestrogens in human urine from several Asian countries

Intake of a diet rich in phytoestrogens has been associated with a decreased risk for hormone-dependent cancers in humans. Biomonitoring of phytoestrogens in human urine has been used to assess the intake of phytoestrogens. Although studies have reported phytoestrogen levels in urine specimens from the United States and Japan, little is known of human intake of phytoestrogens in other Asian countries. In this study we determined the concentrations of seven phytoestrogens, namely, enterolactone, enterodiol, daidzein, equol, O-desmethylangolensin (O-DMA), genistein, and coumestrol, in 199 human urine samples from three Asian countries, Vietnam (Hanoi and Ho Chi Minh), Cambodia (Phnom Penh), and India (Chennai and Kolkata), using a simple, sensitive, and reliable liquid chromatography (LC)-tandem mass spectrometry (MS/MS) method. The residue levels of phytoestrogens in urine samples from the three Asian countries were compared with the concentrations in 26 urine samples from Japan (Ehime) and 16 urine samples from the United States (Albany), analyzed in this study. Among the phytoestrogens analyzed, isoflavones such as daidzein and genistein were predominant in urine samples from Vietnam; samples from Cambodia and India contained higher concentrations of enterolactone than isoflavones. Urinary concentrations of isoflavones in samples from Hanoi, Vietnam, were notably higher than the concentrations in samples from Cambodia, India, and the United States and similar to the concentrations in samples from Japan. The lowest concentrations of daidzein and the highest concentrations of enterolactone were found in urine samples from India. Concentrations of equol and O-DMA, which are microbial transformation products of daidzein (produced by gut microflora), were notably high in urine samples from Hanoi, Vietnam. The ratios of the concentration of equol or O-DMA to that of daidzein were significantly higher in samples from Hanoi than from Japan, indicating high biotransformation efficiency of daidzein by the population in Hanoi. High concentrations of equol, in addition to isoflavones, in urine have been linked to reduced breast cancer risk in previous studies, and, thus, the Vietnamese population may have potential protective effect against breast cancer. This study suggests that the dietary intake and profiles of phytoestrogens vary considerably, even among Asian countries.

Breast, colorectal, and prostate cancer risk in the European Prospective Investigation into Cancer and Nutrition-Norfolk in relation to phytoestrogen intake derived from an improved database

BACKGROUND

The characterization of phytoestrogen intake and cancer risk has been hindered by the absence of accurate dietary phytoestrogen values.

OBJECTIVE

We examined the risk of breast, colorectal, and prostate cancers relative to phytoestrogen intake on the basis of a comprehensive database.

DESIGN

Demographic and anthropometric characteristics, a medical history, and 7-d records of diet were collected prospectively from participants (aged 40-79 y) in the European Prospective Investigation into Cancer and Nutrition-Norfolk (EPIC-Norfolk). Five hundred nine food items were analyzed by liquid chromatography-mass spectrometry/mass spectrometry, and (13)C(3)-labeled internal standards were analyzed for isoflavones (genistein, daidzein, glycitein, biochanin A, and formononetin), lignans (secoisolariciresinol and matairesinol), and enterolignans from gut microbial metabolism in animal food sources (equol and enterolactone). From the direct analysis, values for 10,708 foods were calculated. Odds ratios (ORs) for breast (244 cases, 941 controls), colorectal (221 cases, 886 controls), and prostate (204 cases, 812 controls) cancers were calculated relative to phytoestrogen intake.

RESULTS

Phytoestrogen intake was not associated with breast cancer among women or colorectal cancer among men. Among women, colorectal cancer risk was inversely associated with enterolactone (OR: 0.33; 95% CI: 0.14, 0.74) and total enterolignans (OR: 0.32; 95% CI: 0.13, 0.79), with a positive trend detected for secoisolariciresinol (OR: 1.60; 95% CI: 0.96, 2.69). A positive trend between enterolignan intake and prostate cancer risk (OR: 1.27; 95% CI: 0.97, 1.66) was attenuated after adjustment for dairy intake (OR: 1.19; 95% CI: 0.77, 1.82).

CONCLUSION

Dietary phytoestrogens may contribute to the risk of colorectal cancer among women and prostate cancer among men.

Phytoestrogen content of foods of animal origin: dairy products, eggs, meat, fish, and seafood

Dietary phytoestrogens may be involved in the occurrence of chronic diseases. Reliable information on the phytoestrogen content in foods is required to assess dietary exposure and disease risk in epidemiological studies. However, existing analyses have focused on only one class of these compounds in plant-based foods, and there is only little information on foods of animal origin, leading to an underestimation of intake. This is the first comprehensive study of phytoestrogen content in animal food. We have determined the phytoestrogen content (isoflavones: biochanin A, daidzein, formononetin, genistein, and glycitein; lignans: secoisolariciresinol and matairesinol; coumestrol; equol; enterolactone; and enterodiol) in 115 foods of animal origin (including milk and milk-products, eggs, meat, fish, and seafood) and vegetarian substitutes using liquid chromatography-mass spectrometry (LC-MS) with (13)C-labeled internal standards. Phytoestrogens were detected in all foods analyzed; the average content was 20 microg/100 g of wet weight (isoflavones, 6 microg/100 g; lignans, 6 microg/100 g; equol, 3 microg/100 g; and enterolignans, 6 microg/100 g). In infant soy formula, 19 221 microg/100 g phytoestrogens were detected (compared to 59 microg/100 g in non-soy formula). Our study shows that all foods analyzed contained phytoestrogens and most foods (except for fish, seafood, and butter) contained mammalian phytoestrogens (enterolignans and equol). This is the first comprehensive study of phytoestrogen content of foods of animal origin and will allow for a more accurate estimation of exposure to dietary phytoestrogens.

Phytoestrogen content of beverages, nuts, seeds, and oils

Phytoestrogens are secondary plant metabolites that have received increasing attention for their bioactivity, in particular due to their structural and functional similarity to 17beta-estradiol. Although urinary and plasma phytoestrogens can be used as biomarkers for dietary intake, this is often not possible in large epidemiological studies or in the assessment of general exposure in free-living individuals. Accurate information about dietary phytoestrogens is therefore important, but there are very limited data concerning food contents. In this study was analyzed a comprehensive selection of tea, coffee, alcoholic beverages, nuts, seeds, and oils for their phytoestrogen content using a newly developed sensitive method based on LC-MS incorporating (13)C 3-labeled standards. Phytoestrogens were detected in all foods analyzed, although the contents in gin and bitter (beer) were below the limit of quantification (1.5 microg/100 g). Lignans were the main type of phytoestrogens detected. Tea and coffee contained up to 20 microg/100 g phytoestrogens and beer (except bitter) contained up to 71 microg/100 g, mainly lignans. As these beverages are commonly consumed, they are a main source of dietary lignans. The results published here will contribute to databases of dietary phytoestrogen content and allow a more accurate determination of phytoestrogen exposure in free-living individuals.

Validation of soy protein estimates from a food-frequency questionnaire with repeated 24-h recalls and isoflavonoid excretion in overnight urine in a Western population with a wide range of soy intakes

BACKGROUND

Evidence of the benefits of soy on cancer risk in Western populations is inconsistent, in part because of the low intake of soy in these groups.

OBJECTIVE

We assessed the validity of soy protein estimates from food-frequency questionnaires (FFQs) in a sample of Adventist Health Study-2 participants with a wide range of soy intakes.

DESIGN

We obtained dietary intake data from 100 men and women (43 blacks and 57 nonblacks). Soy protein estimates from FFQs were compared against repeated 24-h recalls and urinary excretion of daidzein, genistein, total isoflavonoids (TIFLs), and equol (measured by HPLC/photodiode array/mass spectrometry) as reference criteria. We calculated Pearson and Spearman correlation coefficients (with 95% CIs) for FFQ-24-h recall, 24 h-recall-urinary excretion, and FFQ-urinary excretion pairs.

RESULTS

Among soy users, mean (+/- SD) soy protein values were 12.12 +/- 10.80 g/d from 24-h recalls and 9.43 +/- 7.83 g/d from FFQs. The unattenuated correlation (95% CI) between soy protein estimates from 24-h recalls and FFQs was 0.57 (0.32, 0.75). Correlation coefficients between soy protein intake from 24-h recalls and urinary isoflavonoids were 0.72 (0.43, 0.96) for daidzein, 0.67 (0.43, 0.91) for genistein, and 0.72 (0.47, 0.98) for TIFLs. Between FFQs and urinary excretion, these were 0.50 (0.32, 0.65), 0.48 (0.29, 0.61), and 0.50 (0.32, 0.64) for daidzein, genistein, and TIFLs, respectively.

CONCLUSIONS

Soy protein estimates from questionnaire were significantly correlated with soy protein from 24-h recalls and urinary excretion of daidzein, genistein, and TIFLs. The Adventist Health Study-2 FFQ is a valid instrument for assessing soy protein in a population with a wide range of soy intakes.

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.

Lignan content of selected foods from Japan

Lignans constitute a group of phytochemicals widely distributed in the human diet. Once ingested, most dietary lignans are metabolized by the gut microflora to enterolactone and enterodiol, also known as enterolignans. Together with isoflavones and coumestrol, enterolignans have been traditionally classified as phytoestrogens, plant-derived compounds that exhibit estrogen-like activity. In addition to a higher intake of vegetables, many studies have suggested that the presence of phytoestrogens in the Japanese diet is one of the factors that might explain the reduced incidence of certain chronic diseases in Japanese populations compared with Western countries. Being a vegetable-based diet, exposure to dietary lignans should be high, but to assess this exposure, a lignan food database is required. Stable isotope-dilution gas chromatography coupled with mass spectrometry was used to quantify six plant lignans in 86 food items commonly consumed in Japan. These data will complement the previous databases and most importantly expand the knowledge of occurrence of lignans in food to Eastern diets.

Variations in plasma phytoestrogen concentrations in European adults

Dietary phytoestrogens may play a role in chronic disease occurrence. The aim of our study was to assess the variability of plasma concentrations in European populations. We included 15 geographical regions in 9 European countries (Denmark, France, Germany, Greece, Italy, Spain, Sweden, The Netherlands, and UK) and a 16th region, Oxford, UK, where participants were recruited from among vegans and vegetarians. All subjects were participants of the European Prospective Investigation into Cancer and Nutrition (EPIC). Plasma concentrations of 3 isoflavones (daidzein, genistein, and glycitein), 2 metabolites of daidzein [O-desmethylangolensin (O-DMA) and equol] and 2 mammalian lignans (enterodiol and enterolactone) were measured in 1414 participants. We computed geometric means for each region and used multivariate regression analysis to assess the influence of region, adjusted for gender, age, BMI, alcohol intake, smoking status, and laboratory batch. Many subjects had concentrations below the detection limit [0.1 microg/L (0.4 nmol/L)] for glycitein (80%), O-DMA (73%) and equol (62%). Excluding subjects from Oxford, UK, the highest concentrations of isoflavones were in subjects from the Netherlands and Cambridge, UK [2-6 microg/L (7-24 nmol/L); P < 0.05], whereas concentrations for lignans were highest in Denmark [8 microg/L (27 nmol/L); P < 0.05]. Isoflavones varied 8- to 13-fold, whereas lignans varied 4-fold. In the vegetarian/vegan cohort of Oxford, concentrations of isoflavones were 5-50 times higher than in nonvegetarian regions. Region was the most important determinant of plasma concentrations for all 7 phytoestrogens. Despite the fact that plasma concentrations of phytoestrogens in Europe were low compared with Asian populations, they varied substantially among subjects from the 16 different regions.

Dietary phytoestrogen intake is associated with reduced colorectal cancer risk

Evidence suggests dietary phytoestrogens may reduce the risk of certain hormonal cancers (e.g. breast and prostate). There is a paucity of data regarding phytoestrogens and colorectal cancer risk. Phytoestrogens are plant compounds with estrogen-like activities. Main classes include isoflavones (found in legumes such as soy) and lignans (found in grains, seeds, nuts, fruits, and vegetables). Although isoflavones have dominated phytoestrogen cancer research, lignans may be more relevant to North American diets. Food questionnaires and analytic databases have recently been modified to incorporate some lignan information. We conducted a case-control study to evaluate the association between phytoestrogen intake and colorectal cancer risk. Colorectal cancer cases were diagnosed in 1997-2000, aged 20-74 y, identified through the population-based Ontario Cancer Registry, and recruited by the Ontario Familial Colorectal Cancer Registry. Controls were a sex and age-group matched random sample of the population of Ontario. Epidemiologic and food frequency questionnaires were completed by 1095 cases and 1890 control subjects. Multivariate logistic regression analysis was used to obtain adjusted odds ratio (OR) estimates. Dietary lignan intake was associated with a significant reduction in colorectal cancer risk [OR (T3 vs. T1) = 0.73; 95% CI: 0.56, 0.94], as was isoflavone intake [OR (T3 vs. T1) = 0.71; 95% CI: 0.58, 0.86]. We evaluated interactions between polymorphic genes that encode enzymes possibly involved in metabolism of phytoestrogens (CYPs, catechol O-methyl transferase, GSTs, and UGTs) and found no significant effect modification with respect to phytoestrogen intake. This finding that phytoestrogen intake may reduce colorectal cancer risk is important, because dietary intake is potentially modifiable.

Implications of gene-environment interaction in studies of gene variants in breast cancer: an example of dietary isoflavones and the D356N polymorphism in the sex hormone-binding globulin gene

Studies to identify common genetic variants contributing to breast cancer risk often yield inconsistent results. Breast cancer is a complex disease involving both genetic and environmental determinants. Dietary isoflavones are thought to reduce breast cancer risk by stimulating circulating sex hormone-binding globulin (SHBG) levels. The SHBG gene contains a D356N polymorphism and the N variant is associated with reduced SHBG clearance compared with the D variant. In this study, we show a significant gene-environment interaction between SHBG D356N polymorphism and dietary isoflavone exposure on circulating SHBG levels in 1,988 postmenopausal women. SHBG levels were positively associated with isoflavones in women carrying the N variant (etap2 = 1.9%; P = 0.006) but not in women carrying only the D variant (etap2 = 0.0%; P = 0.999; P(interaction) = 0.019). This finding shows that the subtle effects of some genetic variants may be magnified and only become detectable in the presence of certain exposures. This gene-environment interaction might explain heterogeneity in studies associating SHBG gene variants and soy consumption with breast cancer risk in Far East population exposed to high isoflavone levels compared with populations with lower levels.

Isoflavones in breastfed infants after mothers consume soy

BACKGROUND

The bioavailability of isoflavones in children after soy exposure is uncertain.

OBJECTIVE

We aimed to compare isoflavone patterns in infants exposed to isoflavone-containing breast milk (BF), in tofu-fed (TF) infants, and in mothers consuming a soy beverage.

DESIGN

Eighteen nursing mothers who were not feeding soy foods to their infants consumed one daily serving of a soy protein beverage for 2-4 d and collected their own milk and urine and infant urine. Plasma was collected from infants if venous blood draws were ordered by pediatricians. Blood and urine were collected from additional children after they consumed tofu. Isoflavones were measured by liquid chromatography-mass spectrometry.

RESULTS

In 7 subjects, isoflavone values increased significantly from baseline after mothers ate soy: in maternal urine (x +/- SEM) from 18.4 +/- 13.0 to 135.1 +/- 26.0 nmol/mg creatinine, in breast milk from 5.1 +/- 2.2 to 70.7 +/- 19.2 nmol/L, and in infant urine from 29.8 +/- 11.6 to 111.6 +/- 18.9 nmol/mg creatinine. The mean isoflavone concentration in plasma obtained from 11 BF infants was 19.7 +/- 13.2 nmol/L. TF infants had much higher mean isoflavone values (urine, 229 +/- 129 nmol/mg creatinine; plasma, 1049 +/- 403 nmol/L). Statistically significant correlations were observed between the types of fluids investigated within mothers, between mothers and infants, and within infants. Urinary isoflavone excretion per hour adjusted for dose per body weight was 81% lower for BF infants and 24% higher for TF infants than for their mothers after eating soy.

CONCLUSIONS

More isoflavones appear in children than in adults after adjustment for isoflavone intake. Systemic isoflavone exposure in infants can be determined by urinary analysis.

Lignan and isoflavone excretion in relation to uterine fibroids: a case-control study of young to middle-aged women in the United States

BACKGROUND

Uterine fibroids are hormonally responsive; estradiol and progesterone stimulate their growth, and gonadotrophin-releasing hormone agonists shrink them. Phytoestrogens, including isoflavones and lignans, can act as weak estrogens or antiestrogens.

OBJECTIVE

The objective of this case-control study was to evaluate the relation between uterine fibroid risk and phytoestrogen exposure.

DESIGN

Two overnight urine collections (48 h apart) from 170 uterine fibroid cases and 173 controls were analyzed for isoflavonoids (ie, daidzein, genistein, equol, and O-desmethylangolensin) and lignans (enterodiol and enterolactone). Logistic regression was used to determine associations between the mean excretion of the 2 collections and the risk of uterine fibroids.

RESULTS

Unadjusted isoflavone excretion did not differ significantly between cases and controls (2.33 +/- 5.82 and 2.60 +/- 5.90 nmol/mg Cr, respectively; P = 0.68), but cases excreted significantly less lignans than did controls (2.86 +/- 3.45 and 4.57 +/- 6.67 nmol/mg Cr, respectively; P < 0.01). The trend for a reduced risk of uterine fibroids with increasing quartiles of lignan excretion was significant (odds ratio for highest versus lowest quartile = 0.31; 95% CI: 0.17, 0.58; P for trend < 0.01). When adjusted for age, BMI, race, family history of uterine fibroids, and isoflavone excretion, this trend remained but was attenuated (P = 0.07).

CONCLUSIONS

Our findings suggest a modest inverse association between lignan excretion and uterine fibroid risk. Whether this relation represents an effect of lignans per se or of other constituents of lignan-containing foods on the development of uterine fibroids remains to be determined. No association was found between isoflavone excretion and uterine fibroids; however, the intake of soy foods, the primary source of isoflavones, was low in this population.

CYP17 genotype modifies the association between lignan supply and premenopausal breast cancer risk in humans

Cytochrome P450c17alpha (CYP17) has been associated with alterations in steroid hormone levels and premenopausal breast cancer risk and could modify the association between phytoestrogen intake and breast cancer risk. We examined plasma concentrations of enterolactone and genistein, estimated dietary phytoestrogen intake, CYP17 5'-UTR MspA1 genetic polymorphism, and breast cancer risk in 267 premenopausal breast cancer patients and 573 age-matched population controls from Germany. Multivariate logistic regression was used to estimate breast cancer risk associated with quartiles of phytoestrogen intake by genotype and to investigate gene-nutrient interactions. Premenopausal breast cancer risk was not significantly associated with the CYP17 A2 genotype. We observed a significant modifying effect of CYP17 genotype on plasma enterolactone-associated breast cancer risk (P for interaction < 0.01). Plasma enterolactone was significantly inversely related to breast cancer risk only in A2A2 carriers, showing odds ratios and 95% CI of 0.02 (0.00-0.41) and 0.01 (0.00-0.21) for the third and fourth quartiles vs. the lowest quartile, respectively. This inverse association was also found for the calculated enterolignan production as well as matairesinol intake. Compared with A1A1 carriers with the lowest enterolactone supply, the risk reduction associated with a high enterolactone supply resulted in a comparably decreased breast cancer risk for all genotypes. For genistein, no clear indication for a differential effect by CYP17 genotype was obtained. Our results suggest that CYP17 genotype modifies the protective effect of lignans on premenopausal breast cancer risk. Women homozygous for A2 allele benefit most from high plasma enterolactone concentrations and a high consumption of dietary precursors.

The relative bioavailability of enterolignans in humans is enhanced by milling and crushing of flaxseed

Flaxseed is one of the richest sources of lignans and is increasingly used in food products or as a supplement. Plant lignans can be converted by intestinal bacteria into the so-called enterolignans, enterodiol and enterolactone. For a proper evaluation of potential health effects of enterolignans, information on their bioavailability is essential. The aim of this study was to investigate whether crushing and milling of flaxseed enhances the bioavailability of enterolignans in plasma. In a randomized, crossover study, 12 healthy subjects supplemented their diet with 0.3 g whole, crushed, or ground flaxseed/(kg body weight . d). Each subject consumed flaxseed for 10 successive days separated by 11-d run-in/wash-out periods, in which the subjects consumed a diet poor in lignans. Blood samples were collected at the end of each run-in/wash-out period, and at the end of each supplement period. Plasma enterodiol and enterolactone were measured using LC-MS-MS. The mean relative bioavailability of enterolignans from whole compared with ground flaxseed was 28% (P < or = 0.01), whereas that of crushed compared with ground flaxseed was 43% (P < or = 0.01). Crushing and milling of flaxseed substantially improve the bioavailability of the enterolignans.

Intake of the Plant Lignans Secoisolariciresinol, Matairesinol, Lariciresinol, and Pinoresinol in Dutch Men and Women

Enterolignans (enterolactone and enterodiol) are phytoestrogens that are formed by the colonic microflora from plant lignans. They may reduce the risk of certain types of cancer and cardiovascular diseases. Initially, only secoisolariciresinol and matairesinol were considered to be enterolignan precursors, but recently, new precursors such as lariciresinol and pinoresinol were identified. We recently developed a lignan database including 4 major enterolignan precursors. We used this database to estimate lignan intake in a representative sample of Dutch men and women participating in the Dutch Food Consumption Survey, carried out in 1997-1998. Median total lignan intake among 4660 adults (19-97 y old) was 979 microg/d. Total lignan intake did not differ between men and women; thus, the lignan density of the diet was significantly higher (P < 0.001) in women than in men. Lignan intake was strongly skewed toward higher values (range 43-77584 microg/d, mean 1241 microg/d). Lariciresinol and pinoresinol contributed 75% to lignan intake, whereas secoisolariciresinol and matairesinol contributed only 25%. The major food sources of lignans were beverages (37%), vegetables (24%), nuts and seeds (14%), bread (9%), and fruits (7%). Lignan intake was significantly (P < 0.001) correlated with intake of dietary fiber (r = 0.46), folate (r = 0.39), and vitamin C (r = 0.44). Older persons, nonsmokers, vegetarians, and persons with a low BMI or a high socioeconomic status had higher lignan intakes than their counterparts. In brief, this study shows that the amount of enterolignan precursors in the diet has previously been largely underestimated.

The effect of soy consumption on the urinary 2:16-hydroxyestrone ratio in postmenopausal women depends on equol production status but is not influenced by probiotic consumption

Some epidemiologic studies reported an association between a low ratio of urinary 2-hydroxyestrogens (2-hydroxyestradiol + 2-hydroxyestrone) to 16alpha-hydroxyestrone (2:16OHE(1)) and increased breast cancer risk. Some studies show that soy consumption increases this ratio, and it is suggested that this effect may reduce breast cancer risk. We hypothesized that consumption of probiotic bacteria would alter fecal bacteria and enzymes involved in soy isoflavone metabolism, thereby increasing isoflavone bioavailability and enhancing the beneficial effects of soy on estrogen metabolism. Breast cancer survivors (n = 20) and controls (n = 20) were given 4 treatments for 6 wk each, separated by 2-wk washout periods, in a randomized, crossover design: soy protein (26.6 +/- 4.5 g protein/d containing 44.4 +/- 7.5 mg isoflavones/d); soy protein + probiotics (10(9) colony-forming units Lactobacillus acidophilus DDS(R)+1 & Bifidobacterium longum, 15-30 mg fructooligosaccharide/d); milk protein (26.6 +/- 4.5 g protein/d); and milk protein + probiotics. Survivors tended to have a lower baseline urine 2:16OHE(1) ratio than controls (P = 0.10). In the group as a whole, soy consumption tended to increase urinary 2-hydroxyestrogens (P = 0.07) and 16alpha-hydroxyestrone (P = 0.11) but had no effect on the urinary 2:16OHE(1) ratio. When subjects were divided into groups by plasma concentrations and urinary levels of the daidzein metabolite equol, soy increased urinary 2-hydroxyestrogens (P = 0.01) and the 2:16OHE(1) ratio (P = 0.04) only in subjects with high plasma equol concentrations. None of these results were influenced by probiotic consumption. These results are consistent with studies that found lower urine 2:16OHE(1) ratios in women with breast cancer and suggest that soy consumption increases this ratio only in women who are equol producers.

Gut bacterial metabolism of the soy isoflavone daidzein: exploring the relevance to human health

The indigenous intestinal microflora are involved in a variety of processes within the human body, and are important for maintaining host health. As such, interindividual differences in the ability to harbor certain intestinal bacteria might be associated with interindividual differences in health and/or disease susceptibility. In the last decade there has been considerable interest in phytoestrogen intakes in relation to human health. Daidzein, an isoflavone phytoestrogen found in soy, is metabolized to equol and O-desmethylangolensin (O-DMA) by intestinal bacteria. The specific bacterium/bacteria responsible for equol and O-DMA production in humans have yet to be identified definitively, but in vitro and animal studies have suggested that equol and O-DMA are more biologically active than their precursor daidzein. Interestingly, substantial interindividual differences in daidzein metabolism exist; following soy or daidzein consumption, approximately 30%-50% of the human population produce equol, and approximately 80%-90% produce O-DMA. Observational and intervention studies in humans have suggested that the ability to produce equol and O-DMA may be associated with reduced risk of certain diseases including breast and prostate cancers. However, relatively few studies have been conducted to date. In this review, we discuss the available evidence for a relationship between daidzeinmetabolizing phenotypes and human health, and suggest potential mechanisms for some of the reported relationships.