High concordance of daidzein-metabolizing phenotypes in individuals measured 1 to 3 years apart

Particular intestinal bacteria are capable of metabolizing the soya isoflavone daidzein to equol and/or O-desmethylangolensin (O-DMA), and the presence of these metabolites in urine after soya consumption are markers of particular intestinal bacteria profiles. Prevalences of equol producers and O-DMA producers are approximately 30-50 % and 80-90 %, respectively, and limited observations have suggested that these daidzein-metabolizing phenotypes are stable within individuals over time. Characterizing stability of these phenotypes is important to understand their potential as markers of long-term exposure to particular intestinal bacteria and their associations with disease risk. We evaluated concordance within an individual for the equol-producer and O-DMA-producer phenotypes measured at two time points (T1, T2), 1-3 years apart. Phenotypes were ascertained by analysing equol and O-DMA using GC-MS in a spot urine sample collected after 3 d soya (source of daidzein) supplementation. In ninety-two individuals without recent (within 3 months before phenotyping) or current antibiotics use, 41 % were equol producers at T1 and 45 % were equol producers at T2, and 90 % were O-DMA producers at T1 and 95 % were O-DMA producers at T2. The percentage agreement for the equol-producer phenotype was 82 and for the O-DMA-producer phenotype was 89. These results indicate that these phenotypes are stable in most individuals over time, suggesting that they provide a useful biomarker for evaluating disease risk associated with harbouring particular intestinal bacteria responsible for, or associated with, the metabolism of the soya isoflavone daidzein.

Intracranial meningioma and ionizing radiation in medical and occupational settings

In a population-based case-control study of 200 cases and 400 controls in western Washington State, the authors assessed associations between meningioma and ionizing radiation in medical and occupational settings. No significant associations were observed for diagnostic studies or occupational settings, but associations were observed for radiation therapy to head or neck (odds ratio 3.7, 95% CI 1.5 to 9.5), especially for neoplastic conditions. Only four patients (2%) had meningiomas that followed high-dose cranial radiation.

Postmenopausal bone mineral density in relation to soy isoflavone-metabolizing phenotypes

OBJECTIVES

Intestinal bacterial metabolize the soy isoflavone daidzein to O-desmethylangolensin (O-DMA) or equol. Some individuals do not excrete O-DMA or equol after soy consumption, suggesting they do not harbor bacteria capable of producing these metabolites. The aim of this study was to evaluate bone mineral density (BMD) in relation to presence of these urinary metabolites.

METHODS

BMD, determined by whole-body dual X-ray absorptiometry scan, was age-adjusted and evaluated in relation to O-DMA-producer and equol-producer phenotypes in 92 postmenopausal women, aged 50-75 years. Women consumed supplemental soy foods (daidzein source) for 3 days and collected a first-void urine sample on the fourth day in order to determine metabolic phenotypes.

RESULTS

In O-DMA producers (n=76) compared to O-DMA non-producers (n=16), greater total, leg and head BMD (p<0.05) were observed. Total BMD among the O-DMA producers (geometric mean=1.04 g/cm2) was 6% greater than total BMD among the O-DMA non-producers (geometric mean=0.98 g/cm2). Total and site-specific BMD did not differ between equol producers (n=24) and non-producers (n=68) (p>0.05). In exploratory analyses, among regular soy consumers, spinal BMD was 20% lower among the equol producers than non-producers, whereas, among soy non-consumers, no such difference was observed (p-interaction<0.05). Among equol producers, circulating estrone and free estradiol concentrations were inversely or not associated with total BMD, whereas, among equol non-producers, these hormones were positively associated (p-interaction<0.05).

CONCLUSIONS

Our results provide evidence that intestinal bacterial composition may influence BMD in postmenopausal women. Further studies characterizing associations of intestinal bacterial profiles with BMD are warranted.

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.

Familial correlations, segregation analysis, and nongenetic correlates of soy isoflavone-metabolizing phenotypes

Particular intestinal bacteria metabolize the soy isoflavone daidzein to equol and O-desmethylangolensin (O-DMA), metabolites that can be identified in urine. Individuals that harbor bacteria capable of producing equol or O-DMA are known as equol producers (approximately 30%-50% of the population) and O-DMA producers (approximately 80%-90% of the population), respectively. The equol-producer phenotype has been associated with sex hormone-related outcomes in several studies. However, the bacteria responsible for these phenotypes have not yet been identified and factors that influence the manifestation of these phenotypes are not well understood. To evaluate familial clustering of and nongenetic factors associated with these phenotypes, 410 individuals from 112 families participated in phenotyping (3-day soy challenge and Day 4 spot urine collection). In segregation analyses of the equol-producer phenotype, the Mendelian dominant model provided the most parsimonious fit to the data, suggesting that the pattern of inheritance of the equol-producer phenotype is consistent with an autosomal dominant trait. This phenotype was positively associated with education (p trend = 0.01), but not with sex, smoking, or several dietary factors. Results of the segregation analyses of the O-DMA-producer phenotype were inconclusive; no other models provided a more parsimonious fit to the data than the general model. This phenotype was inversely associated with age in a nonlinear model (p = 0.01), positively associated with age- and sex-adjusted height (odds ratio [OR] 10-cm increase = 0.38, 95% confidence interval [CI] = 0.15, 0.95) and body mass index (kg/m(2)) (OR = 0.91, 95% CI = 0.85, 0.96), but not with sex, education, smoking, or several dietary factors. These results suggest the equol-producer phenotype may be under some degree of genetic control and that there are likely other environmental factors not evaluated in the present analysis that contribute to both of these phenotypes. These results provide a foundation for further work to refine our understanding of heritable and environmental determinants of daidzein-metabolizing phenotypes.

Biomechanical properties of shoes and risk of falls in older adults

OBJECTIVES

To determine the relationships between the biomechanical properties of shoes worn in a cohort of healthy older adults and the risk of falling.

DESIGN

Nested case-control study, comparing biomechanical measurements of shoes worn by those who reported a fall with measurements of shoes worn by age- and sex-matched nonfallers engaged in broadly similar activities.

SETTING

On-site measurements where falls occurred.

PARTICIPANTS

A cohort of 1,371 older adults, of whom 327 reported a fall and 327 served as age- and sex-matched controls.

MEASUREMENTS

Shoe measurements related to lateral stability (heel height and width, critical tipping angle), foot position sense (heel-collar height, sole thickness, and sole flexibility), and the shoe/surface interface (foresole material, shoe-to-ground coefficient of friction, sole contact area).

RESULTS

Greater heel height was associated with increased risk of a fall (P for trend=.03), whereas greater sole contact area was associated with reduced risk (P for trend=.005). Shoe characteristics related to foot position sense bore little apparent relation to fall risk. Coefficients of friction of 0.5 or greater were observed in 93% of shoes measured, indicating that very few were excessively slippery.

CONCLUSION

Certain measurable properties of shoes were found to be significantly related to risk of falls in older adults. Wearing shoes with low heels and large contact area may help older adults reduce the risk of a fall in everyday settings and activities.

Footwear style and risk of falls in older adults

OBJECTIVES

To determine how the risk of a fall in an older adult varies in relation to style of footwear worn.

DESIGN

Nested case-control study.

SETTING

Group Health Cooperative, a large health maintenance organization in Washington state.

PARTICIPANTS

A total of 1,371 adults aged 65 and older were monitored for falls over a 2-year period; 327 qualifying fall cases were compared with 327 controls matched on age and sex.

MEASUREMENTS

Standardized in-person examinations before fall occurrence, interviews about fall risk factors after the fall occurred, and direct examination of footwear were conducted. Questions for controls referred to the last time they engaged in an activity broadly similar to what the case was doing at the time of the fall.

RESULTS

Athletic and canvas shoes (sneakers) were the styles of footwear associated with lowest risk of a fall. Going barefoot or in stocking feet was associated with sharply increased risk, even after controlling for measures of health status (adjusted odds ratio=11.2, 95% confidence interval (CI)=2.4-51.8). Relative to athletic/canvas shoes, other footwear was associated with a 1.3-fold increase in the risk of a fall (95% CI=0.9-1.9), varying somewhat by style.

CONCLUSION

Contrary to findings from gait-laboratory studies, athletic shoes were associated with relatively low risk of a fall in older adults during everyday activities. Fall risk was markedly increased when participants were not wearing shoes.

Mammographic density in relation to daidzein-metabolizing phenotypes in overweight, postmenopausal women

Circulating hormones are associated with mammographic density, an intermediate marker of breast cancer risk. Differences in circulating hormones, including estrone and testosterone, have been observed in premenopausal women based on their capacity to metabolize daidzein, an isoflavone found predominantly in soybeans. Equol and O-desmethylangolensin (O-DMA) are products of intestinal bacterial metabolism of daidzein. There is interindividual variability in the capacity to produce daidzein metabolites; individuals can be equol producers or non-producers and O-DMA producers or non-producers. We tested the hypothesis that daidzein-metabolizing phenotypes are associated with mammographic density. Participants were recruited from among 92 sedentary, postmenopausal women, ages 50 to 75 years, who participated in a 1-year physical activity intervention. Pre-intervention mammographic density was determined using a computer-assisted, gray-scale thresholding technique. Fifty-five of these women consumed supplemental soy protein (>10 mg daidzein/d) for 3 days and collected a first-void urine sample on the fourth day to determine daidzein-metabolizing phenotypes. Equol and O-DMA concentrations were measured using gas chromatography-mass spectrometry. Associations between daidzein-metabolizing phenotypes and percent mammographic density were adjusted for age, maximum adult weight, gravidity, family history of breast cancer, and serum follicle-stimulating hormone and free testosterone concentrations. Mammographic density was 39% lower in equol producers compared with non-producers (P = 0.04). O-DMA producers had mammographic density 69% greater than non-producers (P = 0.05). These results suggest that particular intestinal bacterial profiles are associated with postmenopausal mammographic density, and these associations are not entirely explained by differences in reproductive or anthropometric characteristics or circulating hormones.

Serum steroid hormones, sex hormone-binding globulin concentrations, and urinary hydroxylated estrogen metabolites in post-menopausal women in relation to daidzein-metabolizing phenotypes

Equol and O-desmethylangolensin (O-DMA) are products of bacterial metabolism of daidzein, an isoflavone in soybeans; thus, the presence or absence of equol and/or O-DMA in urine is a marker of particular intestinal bacteria profiles. Plasma hormone concentrations may be lower in pre-menopausal women who harbor the bacteria capable of producing equol (equol producers) compared to women who do not (equol non-producers). We evaluated concentrations of serum hormones, sex hormone-binding globulin (SHBG), and urinary 2-hydroxyestrone (2-OH E(1)) and 16alpha-hydroxyestrone (16alpha-OH E(1)) in relation to equol-producer and O-DMA-producer phenotypes in 89 post-menopausal women. Follicle stimulating hormone (FSH) was 23% greater in O-DMA-producers compared to non-producers (P = 0.04). No significant differences in serum estrogens, androgens, metabolic hormones, or SHBG were observed in relation to either daidzein-metabolizing phenotype. Compared with non-producers within each phenotype, age-adjusted 2-OH E(1):16alpha-OH E(1) was 27% greater (P = 0.06) in equol-producers and 9% greater (P > 0.10) in O-DMA-producers, and 2-OH E(1) concentrations were 24% greater in equol producers (P = 0.07) and 42% greater in O-DMA producers (P = 0.02). No significant differences in 16alpha-OH E(1) were observed in relation to either phenotype. These results suggest that interindividual variability in intestinal bacteria may be related to differences in products of hormone metabolism in post-menopausal women.

Validation of a soy food-frequency questionnaire and evaluation of correlates of plasma isoflavone concentrations in postmenopausal women

BACKGROUND

Soy foods may have various health benefits, but little is known about the patterns and correlates of soy consumption among postmenopausal women in the United States.

OBJECTIVE

We assessed the reliability and validity of a soy food-frequency questionnaire (FFQ) and examined demographic, lifestyle, and dietary correlates of plasma isoflavone concentrations in postmenopausal women.

DESIGN

In this cross-sectional study, soy isoflavone intake and plasma isoflavone concentration were analyzed in 96 postmenopausal women aged 50-79 y; the data were obtained at 2 visits that were 1 wk apart. Intake was determined with a 20-item soy FFQ and a comprehensive FFQ that included questions about tofu and soymilk. Fasting plasma daidzein and genistein concentrations were determined with liquid chromatography-mass spectrometry.

RESULTS

Intraclass correlations between week 1 and week 2 values were >0.98 for both the soy and comprehensive FFQs. Median reported isoflavone intake was <2 mg/d. Pearson's product-moment correlation coefficients relating isoflavone intakes with plasma isoflavone concentrations ranged from 0.35 to 0.43. Plasma isoflavone concentrations were positively associated with age, fiber consumption, servings of fruit and vegetables, and dietary supplement use and were inversely associated with caffeine consumption; no associations with body mass index, education, dietary beliefs, activity level, alcohol intake, or fat intake were observed.

CONCLUSIONS

Within a population with low soy consumption, the soy FFQ and comprehensive FFQ showed good reliability and moderate validity. Associations of plasma isoflavone concentrations with other dietary behaviors suggest that these compounds may serve as biomarkers of health behaviors in populations with low soy consumption.

Validation of a soy food frequency questionnaire with plasma concentrations of isoflavones in US adults

OBJECTIVE

To validate assessment of soy intake using food frequency questionnaires (FFQs) compared with plasma isoflavone (genistein and daidzein) concentrations.

DESIGN

Cross-sectional analysis of soy isoflavone intake and plasma analysis of isoflavones.

SUBJECTS

77 men and women, age range 20 to 40 years, recruited from the Seattle metropolitan area.

MAIN OUTCOME MEASURES

Isoflavone intake was determined from responses to a 40-item soy FFQ and from tofu and soymilk intake assessed as part of a comprehensive FFQ used for the Women's Health Initiative (WHI FFQ). Isoflavone concentrations in fasting blood samples were determined by liquid chromatography-mass spectrometry.

STATISTICAL ANALYSES

Correlation coefficients were calculated for: a) isoflavone intake assessed by the soy FFQ and the WHI FFQ, b) intake assessed by the soy FFQ and plasma isoflavone concentrations, and c) intake assessed by the WHI FFQ and plasma isoflavone concentrations.

RESULTS

Isoflavone intake was highly correlated between the soy FFQ and the WHI FFQ (r = 0.84). Genistein and daidzein intakes determined by the soy FFQ were significantly correlated with plasma concentrations (r = 0.53 and 0.45, respectively). Isoflavone intake assessed from the WHI FFQ was also correlated with plasma concentration (r = 0.46 and 0.45). Soymilk and tofu were the two major contributors to isoflavone intake (38.6%).

CONCLUSIONS

A soy-specific, 40-item FFQ assessed isoflavone intake with good validity. Isoflavone intake assessed by the WHI FFQ (tofu and soymilk) had lower correlations with plasma concentrations compared with the soy FFQ. Nonetheless, assessment of the two foods is a reasonably good marker for soy food consumption in this sample.