Usual dietary isoflavone intake and reproductive function across the menstrual cycle

The role of soy and soy isoflavones on women's fertility and related outcomes: an update

Soy is a key food in human nutrition. It is widely used in eastern traditional cuisine and it has recently diffused among self-conscious and vegetarian diets. The success of soy mainly depends on versatility and supposed healthy properties of soy foods and soy components. Meanwhile, the possible influence on endocrine system, in particular by isoflavones, raised concerns among some researchers. The present paper aims to conduct a review of available data on the effect of soy, soy foods and soy components on women's fertility and related outcomes. Eleven interventional studies, eleven observational studies and one meta-analysis have been selected from the results of queries. A weak, not clinically relevant effect has been highlighted on cycle length and hormonal status. However, a suggestive positive influence has been shown among women with fertility issues and during assisted reproductive technologies. Overall, soy and soy components consumption do not seem to perturb healthy women's fertility and can have a favourable effect among subjects seeking pregnancy. However, because of the paucity of studies exploring the impact of soy intake on women's fertility, as well as the limited population sample size, the frequently incomplete specimens’ collection to investigate all cycle phases and the insufficient characterisation of participants, the evidence is suggestive and it needs further in-depth research taking into account all these aspects.

Isoflavone biomarkers are inversely associated with atherosclerosis progression in adults: a prospective study

BACKGROUND

Many studies have examined associations between dietary isoflavones and atherosclerosis, but few used objective biomarkers.

OBJECTIVES

We examined the associations of isoflavone biomarkers (primary analyses) and equol production (secondary analyses) with the progression of carotid intima-media thickness (cIMT), and whether inflammation, systolic blood pressure (SBP), blood lipids, and sex hormone-binding globulin (SHBG) mediated these associations, in Chinese adults.

METHODS

This 8.8-y prospective study included 2572 subjects (40-75 y old) from the GNHS (Guangzhou Nutrition and Health Study; 2008-2019). The concentrations of daidzein, genistein, and equol were assayed by an HPLC-tandem MS in serum (n = 2572) at baseline and in urine (n = 2220) at 3-y intervals. The cIMT of the common carotid artery (CCA) and bifurcation segment were measured by B-mode ultrasound every 3 y, and the progressions of cIMT ( ∆cIMT) were estimated using the regression method.

RESULTS

Multivariable linear mixed-effects models (LMEMs) and ANCOVA revealed that subjects with higher serum isoflavones tended to have lower increases of CCA-cIMT. The mean ± SEM differences in 8.8-y ∆CCA-cIMT between extreme tertiles of serum isoflavones were -17.1 ± 8.4, -20.6 ± 8.3, and -23.3 ± 10.4 μm for daidzein, total isoflavone, and equol (P-trends < 0.05), respectively. LMEMs showed that the estimated yearly changes (95% CIs) (μm/y) in CCA-IMT were -2.0 (-3.8, -0.3), -1.9 (-3.6, -0.1), and -2.1 (-3.8, -0.3) in the highest (compared with the lowest) tertile of daidzein, genistein, and total isoflavones, respectively (P-interaction < 0.05). Path analyses indicated that the serum equol-atherosclerosis association was mediated by increased SHBG and decreased SBP. Similar beneficial associations were observed in the secondary analyses.

CONCLUSIONS

Serum isoflavones and equol exposure were associated with reduced cIMT progression, mediated by SHBG and SBP.

Low Intake of Vegetable Protein is Associated With Altered Ovulatory Function Among Healthy Women of Reproductive Age

CONTEXT

Diets high in plant-based protein have gained popularity due to increasing health concerns regarding consumption of animal products. Though links between intakes of certain protein-rich foods and reproductive disorders have been suggested, the relationship of overall animal and vegetable proteins with reproductive hormones among reproductive-aged women is unknown.

OBJECTIVE

To evaluate the associations between the intake of dietary protein with reproductive hormones and sporadic anovulation among reproductive-aged women.

DESIGN

A prospective cohort study, 2005-2007.

SETTING

University at Buffalo, western New York, United States.

PARTICIPANTS

A total of 259 premenopausal women (18-44 years) without dietary restrictions.

MAIN OUTCOME MEASURE(S)

Serum reproductive hormones were determined up to 8 times per cycle for 2 cycles. Protein intake was assessed the day prior to hormone assessment at 4 visits/cycle using 24-hour recalls.

RESULTS

Overall, 84% of participants met the recommended dietary allowance for total protein set for reproductive-aged women. Neither total nor animal protein intake were associated with reproductive hormones or anovulation. However, vegetable protein intake in the lowest tertile was associated with lower luteal phase progesterone (-18.0%, 95% confidence interval [CI] -30.2, -3.6), higher follicle-stimulating hormone (3.8%, 95% CI 0.2, 7.6), and a higher risk of anovulation (risk ratio [RR] 2.53, 95% CI 1.21, 5.26), compared with the middle tertile. Nuts and seeds were the only protein-rich foods associated with an elevated risk of anovulation (RR 2.12, 95% CI 1.17, 3.85).

CONCLUSIONS

Findings suggest that among women who meet the recommended dietary allowance for total protein, low intake of vegetable, but not animal, protein may disturb normal ovulatory function.

Estrogen receptor modulation of some polyphenols extracted from Daucus carota as a probable mechanism for antifertility effect: An in silico study

The seeds of Daucus carota, traditionally used by women in many countries to prevent conception, were proved to have negative impact on reproductive hormone levels as well as on the estrous cycles in albino mice affecting the fertility status. This study is an attempt to investigate the possible role of polyphenols present in the seeds in hampering the reproductive processes. The Molecular Docking, Molecular Dynamics (MD) simulation and binding free energy calculation studies reveal that six polyphenols present in the seeds can bind with the active sites of human Estrogen Receptor (ER) and may interfere in the estrogen signaling in human. These polyphenols were found to bind to a conservative pocket of ER[Formula: see text], which is comprised of residues 343–388, 421–428 and 525–540. Docking studies indicated the presence of strong hydrogen bonding, pi–pi interactions and numerous hydrophobic interactions that stabilize the ER[Formula: see text]-polyphenol complexes.

The docked complexes were further subjected to MM/GBSA analysis to calculate binding free energies. Molecular dynamic simulation studies carried out for a period of 20[Formula: see text]ns revealed low RMS deviation values suggesting high accuracy of the docking poses and stability of the complexes. Out of the six polyphenols, catechin and epicatechin have shown highest binding affinity towards the ER[Formula: see text] receptor. These findings will help in identifying ER modulators of plant origin targeting ER alpha and predicting their effects on the reproductive hormone homeostasis. Moreover, this study may form preliminary basis for further identification of potential herbal antifertility agents.

Dietary phytoestrogen intakes of adult women are not strongly related to fecundability in 2 preconception cohort studies

BACKGROUND

Phytoestrogens are plant-derived hormonally active compounds found in soy, cruciferous vegetables, nuts, and seeds. Although phytoestrogens have been associated with altered endogenous hormonal activity, luteal phase deficiency, and reduced endometrial decidualization, the literature reporting examinations of phytoestrogen intake and fertility presents mixed findings.

OBJECTIVES

We sought to evaluate prospectively the association between dietary phytoestrogen intake (isoflavones, lignans, and coumestans) and fecundability, the per-cycle probability of conception, in 2 cohorts of women planning pregnancy.

METHODS

Pregnancy Study Online (PRESTO) and Snart Foraeldre (SF) are parallel web-based preconception cohort studies of women from North America and Denmark, respectively, who are trying to conceive. Participants complete an online baseline questionnaire on sociodemographic, lifestyle, and medical factors. We ascertained intake of individual phytoestrogens from validated FFQs. We measured fecundability using data on menstruation and pregnancy status from bimonthly follow-up questionnaires. We analyzed data from 4880 PRESTO and 2898 SF female study participants who had been attempting conception for ≤6 cycles at study entry. We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% CIs.

RESULTS

Phytoestrogen intake varied across cohorts, yet was associated with higher socioeconomic status and healthier behaviors in both cohorts. After adjustment for potential confounders, phytoestrogen intake was not substantially associated with fecundability in either cohort. We observed some evidence of improved fecundability with increasing isoflavone intake among women age ≥30 years in PRESTO (FR: 1.12; 95% CI: 0.94, 1.34, for comparison of ≥90th with <25th percentile intake) and SF (corresponding FR: 1.19; 95% CI: 0.92, 1.55). Lignan intake was associated with slightly increased fecundability in SF (FR for comparison of 75th to 90th with <25th percentile: 1.10; 95% CI: 0.96, 1.26), but decreased fecundability in PRESTO (FR for comparison of ≥90th with <25th percentile: 0.83; 95% CI: 0.72, 0.97).

CONCLUSIONS

We did not observe strong associations between phytoestrogen intake and prospectively-measured fecundability among North American or Danish pregnancy planners.

Urinary Phytoestrogens and Relationship to Menstrual Cycle Length and Variability Among Healthy, Eumenorrheic Women

Context

Phytoestrogens may influence fecundability, although biological mechanisms remain elusive. Since it is hypothesized that phytoestrogens may act through influencing hormone levels, we investigated associations between phytoestrogens and menstrual cycle length, a proxy for the hormonal milieu, in healthy women attempting pregnancy.

Design

A population-based prospective cohort of 326 women ages 18 to 40 with self-reported cycles of 21 to 42 days were followed until pregnancy or for 12 months of attempting pregnancy.

Methods

Urinary genistein, daidzein, O-desmethylangolensin, equol, enterodiol, and enterolactone were measured upon enrollment. Cycle length was determined from fertility monitors and daily journals. Linear mixed models assessed associations with continuous cycle length and were weighted by the inverse number of observed cycles. Logistic regression models assessed menstrual regularity (standard deviation > 75th vs ≤ 75th percentile). Models were adjusted for age, body mass index, race, creatinine, exercise, supplements, lipids, lead, cadmium, cotinine, parity, alcohol, and other phytoestrogens.

Results

Individual phytoestrogens were not associated with cycle length, although total phytoestrogens were associated with shorter cycles (-0.042 days; 95% confidence interval [CI], -0.080 to -0.003, per 10% increase). Each 1 nmol/L increase in enterolactone (odds ratio [OR] 0.88; 95% CI, 0.79-0.97) and total lignans (OR 0.85; 95% CI, 0.76-0.95) was associated with reduced irregularity, and each 1 nmol/L increase in genistein with irregularity (OR 1.19; 95% CI, 1.02-1.38).

Conclusion

Phytoestrogens were not meaningfully associated with cycle length but may be associated with menstrual regularity, among women with self-reported regular cycles. These results highlight differences between isoflavones and lignans and are reassuring for women attempting pregnancy.