Application of dietary phenolic biomarkers in epidemiology: past, present, and future

Performance of Urinary Phenyl-γ-Valerolactones as Biomarkers of Dietary Flavan-3-ol Exposure

BACKGROUND

Phenyl-γ-valerolactones (PVLs) have been identified as biomarkers of dietary flavan-3-ol exposure, although their utility requires further characterization.

OBJECTIVES

We investigated the performance of a range of PVLs as biomarkers indicative of flavan-3-ol intake.

METHODS

We report the results of 2 companion studies: a 5-way randomized crossover trial (RCT) and an observational cross-sectional study. In the RCT (World Health Organization, Universal Trial Number: U1111-1236-7988), 16 healthy participants consumed flavan-3-ol-rich interventions (of apple, cocoa, black tea, green tea, or water [control]) for 1 d each. First morning void samples and 24-h urine samples were collected with diet standardized throughout. For each participant, 1 intervention period was extended (to 2 d) to monitor PVL kinetics after repeat exposure. In the cross-sectional study, 86 healthy participants collected 24-h urine samples, and concurrent weighed food diaries from which flavan-3-ol consumption was estimated using Phenol-Explorer. A panel of 10 urinary PVLs was quantified using liquid chromatography tandem mass spectrometry.

RESULTS

In both studies, 2 urinary PVLs [5-(3'-hydroxyphenyl)-γ-valerolactone-4'-sulfate and putatively identified 5-(4'-hydroxyphenyl)-γ-valerolactone-3'-glucuronide] were the principal compounds excreted (>75%). In the RCT, the sum of these PVLs was significantly higher than the water (control) after each intervention; individually, there was a shift from sulfation toward glucuronidation as the total excretion of PVLs increased across the different interventions. In the extended RCT intervention period, no accumulation of these PVLs was observed after consecutive days of treatment, and after withdrawal of treatment on the third day, there was a return toward negligible PVL excretion. All results were consistent, whether compounds were measured in 24-h urine or first morning void samples. In the observational study, the sum of the principal PVLs correlated dose dependently (Rs = 0.37; P = 0.0004) with dietary flavan-3-ol intake, with similar associations for each individually.

CONCLUSIONS

Urinary 5-(3'-hydroxyphenyl)-γ-valerolactone-4'-sulfate and putatively identified 5-(4'-hydroxyphenyl)-γ-valerolactone-3'-glucuronide are recommended biomarkers for dietary flavan-3-ol exposure.

Contribution of the diverse experimental models to unravelling the biological scope of dietary (poly)phenols

The health benefits associated with (poly)phenols need to be supported by robust and insightful information on their biological effects. The use of in vitro, ex vivo, and in vivo models is crucial to demonstrate functionalities in specific targets. In this regard, bioaccessibility, bioavailability, and tissue/organ distribution need to be fully understood and established. In addition, the structure-function relationships, concerning both descriptive and mechanistic information, between specific compounds and therapeutic objectives, need to be supported by results obtained from in vivo studies. Nevertheless, these studies are not always possible or have some limitations, particularly concerning the mechanistic information explaining the health benefits provided that should be covered with complementary experimental models. Based on these premises, this review aims to overview the contribution of the separate experimental approaches to gain insights into the bioaccessibility, bioavailability, and bioactivity of (poly)phenols. To achieve this objective, recent evidence available on the linkage of healthy/functional foods with the incidence of non-communicable pathologies is presented. The different experimental approaches provide complementary information that allows advances to be applied to the knowledge gained on the functional properties and mechanistic facts responsible for the health attributions of polyphenols. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Characterizing patterns of dietary exposure using metabolomic profiles of human biospecimens: a systematic review

CONTEXT

Establishing diet-disease associations requires reliable assessment of dietary intake. With the rapid advancement of metabolomics, its use in identifying objective biomarkers of dietary exposure has substantially increased.

OBJECTIVE

The aim of our review was to systematically combine all observational studies linking dietary intake patterns with metabolomic profiles of human biospecimens.

DATA SOURCES

Five databases were searched - MEDLINE, Embase, Scopus, Web of Science, and Cochrane CENTRAL - to March 2020.

DATA EXTRACTION

Of the 14 328 studies initially screened, 35 observational studies that met the specified inclusion criteria were included.

DATA ANALYSIS

All reviewed studies indicated that metabolomic measures were significantly correlated with dietary patterns, demonstrating the potential for using objective metabolomic measures to characterize individuals' dietary intake. However, similar dietary patterns did not always result in similar metabolomic profiles across different study populations.

CONCLUSION

Metabolomic profiles reflect a multitude of factors, including diet, genetic, phenotypic, and environmental influences, thereby providing a more comprehensive picture of the impact of diet on metabolism and health outcomes. Further exploration of dietary patterns and metabolomic profiles across different population groups is warranted.

Lignan exposure: a worldwide perspective

Dietary lignans are phytoestrogens that are mostly found in plant-based foods, especially whole grains, seeds, nuts, legumes and vegetables. An accurate assessment of lignan exposure is crucial to evaluate their potential health benefits and to establish future recommendations and dietary guidelines. This narrative review aimed to (i) summarize the pros and the cons of the current main assessment methods for lignan exposure─i.e., dietary questionnaires, food composition tables and biomarkers, (ii) describe the individual lignans more consumed from a worldwide perspective, as well as their main food sources, (iii) determine the lignans concentrations in both urine and blood, and explore their heterogeneity among countries, and finally (iv) discuss the main determinants of lignan exposure.

Urinary Concentrations of (+)-Catechin and (-)-Epicatechin as Biomarkers of Dietary Intake of Flavan-3-ols in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study

This study examines the correlation of acute and habitual dietary intake of flavan-3-ol monomers, proanthocyanidins, theaflavins, and their main food sources with the urinary concentrations of (+)-catechin and (-)-epicatechin in the European Prospective Investigation into Cancer and Nutrition study (EPIC). Participants (N = 419, men and women) provided 24-h urine samples and completed a 24-h dietary recall (24-HDR) on the same day. Acute and habitual dietary data were collected using a standardized 24-HDR software and a validated dietary questionnaire, respectively. Intake of flavan-3-ols was estimated using the Phenol-Explorer database. Concentrations of (+)-catechin and (-)-epicatechin in 24-h urine were analyzed using tandem mass spectrometry after enzymatic deconjugation. Simple and partial Spearman's correlations showed that urinary concentrations of (+)-catechin, (-)-epicatechin and their sum were more strongly correlated with acute than with habitual intake of individual and total monomers (acute rpartial = 0.13-0.54, p < 0.05; and habitual rpartial = 0.14-0.28, p < 0.01), proanthocyanidins (acute rpartial = 0.24-0.49, p < 0.001; and habitual rpartial = 0.10-0.15, p < 0.05), theaflavins (acute rpartial = 0.22-0.31, p < 0.001; and habitual rpartial = 0.20-0.26, p < 0.01), and total flavan-3-ols (acute rpartial = 0.40-0.48, p < 0.001; and habitual rpartial = 0.23-0.33, p < 0.001). Similarly, urinary concentrations of flavan-3-ols were weakly correlated with both acute (rpartial = 0.12-0.30, p < 0.05) and habitual intake (rpartial = 0.10-0.27, p < 0.05) of apple and pear, stone fruits, berries, chocolate and chocolate products, cakes and pastries, tea, herbal tea, wine, red wine, and beer and cider. Moreover, all comparable correlations were stronger for urinary (-)-epicatechin than for (+)-catechin. In conclusion, our data support the use of urinary concentrations of (+)-catechin and (-)-epicatechin, especially as short-term nutritional biomarkers of dietary catechin, epicatechin and total flavan-3-ol monomers.

Food frequency questionnaire is a valid assessment tool of quercetin and kaempferol intake in Iranian breast cancer patients according to plasma biomarkers

In epidemiological and clinical studies, the most common nutritional tool to assess dietary flavonol intake is the food frequency questionnaire (FFQ), which needs to contain a detailed list of plant-based foods and be previously validated. Our study aimed to assess the accuracy of dietary flavonol (quercetin, kaempferol, and isorhamnetin) intake from a food frequency questionnaire (FFQ) compared to fasting plasma flavonol concentrations, as biomarkers of exposure, in breast cancer patients. In a consecutive case series, newly diagnosed patients with breast cancer (n = 140) were recruited at Nour-Nejat Hospital, Tabriz, Iran. Flavonol intake was assessed using a validated FFQ. Plasma flavonol concentrations were measured using high-performance liquid chromatography-ultraviolet detection. The accuracy of dietary status was evaluated using a receiver operating characteristic (ROC) and area under the ROC curve (AUC). Dietary status was shown in dichotomous using ROC-cutoff point. The plasma concentrations of quercetin were moderately correlated with dietary intake of quercetin (Spearman's correlation coefficient (r_s) = 0.188, P < .05; r_partial= 0.330, P < .01) and plasma concentrations of isorhamnetin (r_s = 0.337, P < .001). A linear correlation between dietary levels and plasma concentrations of kaempferol was attained (r_partial = 0.240, P < .05). Using a ROC-cutoff of 61.9 nmol/L for plasma quercetin (test reference), we were able to differentiate between lower and higher consumers of quercetin with an AUC_{ROC-based reference} =0.65 (P < .01, sensitivity = 61.8%, and specificity = 60.0%). Using a plasma kaempferol concentration of 60.1 nmol/L (ROC-cutoff), it was possible to detect significant differences between higher and lower intakes of kaempferol (AUC_{ROC-based reference} = 0.64, P < .05). The correlations and diagnostic performance with plasma concentrations could present a significant accuracy rate (validity), which seems acceptable for a nutritional questionnaire (FFQ) to assess intakes intake levels of quercetin and kaempferol. An improvement in the accuracy of the flavonol exposure can provide more precise relationship with health outcomes, which may increase their clinical significance.

Blood polyphenol concentrations and differentiated thyroid carcinoma in women from the European Prospective Investigation into Cancer and Nutrition (EPIC) study

BACKGROUND

Polyphenols are natural compounds with anticarcinogenic properties in cellular and animal models, but epidemiological evidence determining the associations of these compounds with thyroid cancer (TC) is lacking.

OBJECTIVES

The aim of this study was to evaluate the relations between blood concentrations of 36 polyphenols and TC risk in EPIC (the European Prospective Investigation into Cancer and Nutrition).

METHODS

A nested case-control study was conducted on 273 female cases (210 papillary, 45 follicular, and 18 not otherwise specified TC tumors) and 512 strictly matched controls. Blood polyphenol concentrations were analyzed by HPLC coupled to tandem MS after enzymatic hydrolysis.

RESULTS

Using multivariable-adjusted conditional logistic regression models, caffeic acid (ORlog2: 0.55; 95% CI: 0.33, 0.93) and its dehydrogenated metabolite, 3,4-dihydroxyphenylpropionic acid (ORlog2: 0.84; 95% CI: 0.71, 0.99), were inversely associated with differentiated TC risk. Similar results were observed for papillary TC, but not for follicular TC. Ferulic acid was also inversely associated only with papillary TC (ORlog2: 0.68; 95% CI: 0.51, 0.91). However, none of these relations was significant after Bonferroni correction for multiple testing. No association was observed for any of the remaining polyphenols with total differentiated, papillary, or follicular TC.

CONCLUSIONS

Blood polyphenol concentrations were mostly not associated with differentiated TC risk in women, although our study raises the possibility that high blood concentrations of caffeic, 3,4-dihydroxyphenylpropionic, and ferulic acids may be related to a lower papillary TC risk.

Correlations between urinary concentrations and dietary intakes of flavonols in the European Prospective Investigation into Cancer and Nutrition (EPIC) study

PURPOSE

In this study, we aimed to study the correlation between acute and habitual intakes of flavonols, their main food sources and their 24-h urinary concentrations in an European population.

METHODS

A 24-h dietary recall (24-HDR) and 24-h urine samples were collected on the same day from a convenience subsample of 475 men and women from four countries (France, Italy, Greece and Germany) of the European Prospective Investigation into Cancer and Nutrition (EPIC) study. A standardized 24-HDR software and a country/centre-specific validated dietary questionnaire (DQ) were used to collect acute and habitual dietary data, respectively. The intake of dietary flavonols was estimated using the Phenol-Explorer database. Urinary flavonols (quercetin, isorhamnetin, and kaempferol) were analysed using tandem mass spectrometry with a previous enzymatic hydrolysis.

RESULTS

Weak partial Spearman correlations between both dietary acute and habitual intake and urinary concentrations of quercetin (both Rpartial ~ 0.3) and total flavonols (both Rpartial ~ 0.2) were observed. No significant correlations were found for kaempferol and isorhamentin. Regarding flavonol-rich foods, weak correlations were found between urinary concentrations of quercetin and total flavonols and the acute intake of onions and garlics, fruits, tea, and herbal tea (all Rpartial ~ 0.2). For habitual intake, statistically significant correlations were only found between urinary quercetin concentration and herbal tea (Rpartial = 0.345) and between urinary total flavonol concentration and tea, and herbal tea consumption (Rpartial ~ 0.2).

CONCLUSIONS

Our results suggest that urinary quercetin level can be used as potential concentration biomarkers of both acute and habitual quercetin intake, while urinary concentrations of flavonols are unlikely to be useful biomarkers of individual flavonol-rich foods.

Urinary flavanone concentrations as biomarkers of dietary flavanone intakes in the European Prospective Investigation into Cancer and Nutrition (EPIC) study

In the present study, the aim was to investigate the correlation between the acute and habitual dietary intake of flavanones, their main food sources and the concentrations of aglycones naringenin and hesperetin in 24 h urine in a European population. A 24-h dietary recall (24-HDR) and a 24-h urine sample were collected the same day from a subsample of 475 people from four different countries of the European Prospective Investigation into Cancer and Nutrition study. Acute and habitual dietary data were captured through a standardised 24-HDR and a country/centre-specific validated dietary questionnaire (DQ). The intake of dietary flavanones was estimated using the Phenol-Explorer database. Urinary flavanones (naringenin and hesperetin) were analysed using tandem MS with a previous enzymatic hydrolysis. Weak partial correlation coefficients were found between urinary flavanone concentrations and both acute and habitual dietary flavanone intakes (Rpartial = 0·14-0·17). Partial correlations were stronger between urinary excretions and acute intakes of citrus fruit and juices (Rpartial ∼ 0·6) than with habitual intakes of citrus fruit and juices (Rpartial ∼ 0·24). In conclusion, according to our results, urinary excretion of flavanones can be considered a good biomarker of acute citrus intake. However, low associations between habitual flavanone intake and urinary excretion suggest a possible inaccurate estimation of their intake or a too sporadic intake. For assessing habitual exposures, multiple urinary collections may be needed. These results show that none of the approaches tested is ideal, and the use of both DQ and biomarkers can be recommended.

Adherence to UK dietary guidelines is associated with higher dietary intake of total and specific polyphenols compared with a traditional UK diet: further analysis of data from the Cardiovascular risk REduction Study: Supported by an Integrated Dietary Approach (CRESSIDA) randomised controlled trial

Adherence to dietary guidelines (DG) may result in higher intake of polyphenols via increased consumption of fruits, vegetables and whole grains. We compared polyphenol dietary intake and urinary excretion between two intervention groups in the Cardiovascular risk REduction Study: Supported by an Integrated Dietary Approach study: a 12-week parallel-arm, randomised controlled trial (n 161; sixty-four males, ninety-seven females; aged 40-70 years). One group adhered to UK DG, whereas the other group consumed a representative UK diet (control). We estimated polyphenol dietary intake, using a 4-d food diary (4-DFD) and FFQ, and analysed 24-h polyphenol urinary excretion by liquid chromatography-tandem MS on a subset of participants (n 46 control; n 45 DG). A polyphenol food composition database for 4-DFD analysis was generated using Phenol-Explorer and USDA databases. Total polyphenol intake by 4-DFD at endpoint (geometric means with 95 % CI, adjusted for baseline and sex) was significantly higher in the DG group (1279 mg/d per 10 MJ; 1158, 1412) compared with the control group (1084 mg/d per 10 MJ; 980, 1197). The greater total polyphenol intake in the DG group was attributed to higher intake of anthocyanins, proanthocyanidins and hydroxycinnamic acids, with the primary food sources being fruits, cereal products, nuts and seeds. FFQ estimates of flavonoid intake also detected greater intake in DG compared with the control group. 24-h urinary excretion showed consistency with 4-DFD in their ability to discriminate between dietary intervention groups for six out of ten selected, individual polyphenols. In conclusion, following UK DG increased total polyphenol intake by approximately 20 %, but not all polyphenol subclasses corresponded with this finding.

Application of Urinary Polyphenol Biomarkers Measured by Liquid Chromatography Tandem Mass Spectrometry to Assess Polyphenol Intake and Their Association with Overweight and Obesity in Free-Living Healthy Subjects

Although some polyphenol biomarkers in serum or urine have been identified by untargeted metabolomics and proved to reflect dietary polyphenol intake, only a few of them have been validated in different studies and populations with simple and reliable targeted methods. In the present study, a targeted metabolomics method by LC/MS/MS for the measurement of twenty-two polyphenol biomarkers in urine samples was established and validated to effectively assess the habitual polyphenol intake in free-living healthy Chinese subjects. Multivariate logistic regression models were used to assess relationships of biomarkers with overweight and obesity after adjusting for potential confounders. The levels of urinary polyphenol biomarkers, especially gut microbial metabolites of polyphenols, were inversely associated with overweight and obesity, and this association was more pronounced in the inflammatory groups, suggesting that it is of great importance to maintain polyphenol biomarkers at high levels or intake-sufficient polyphenols in obesity with chronic inflammation than others. The measurement of these biomarkers may offer a valid alternative or complementary addition to self-reported survey for the evaluation of polyphenol intake and investigation into their relationships with chronic disease-related endpoints in large-scale clinical and epidemiologic studies.

Validation of a food frequency questionnaire assessing dietary polyphenol exposure using the method of triads

When conducting research on polyphenols and their effects on health, it is of primary importance to use standardised and validated dietary assessment tools. This paper aims at assessing the validity of a food frequency questionnaire (FFQ) for quantifying dietary polyphenol exposure among healthy adults using the method of triads. Fifty-three healthy adults, aged 20-60, were included in the study. Total dietary polyphenol intake (TDP) estimated by the FFQ was compared with TDP measured by a 3-day food record (FR) and with urinary excretion levels of total polyphenols (TUP). Pearson correlations were calculated between methods. Validity coefficients (VC) were estimated between the three measurements and the 'unknown' true intake. There was a strong correlation between both dietary methods (r = 0.70, p < 0.0001). A moderate but significant association was observed between FFQ-derived TDP and TUP (r = 0.32, p = 0.020). The method of triads yielded a VC for the FFQ of 0.63 (95%CI: 0.41-0.84), indicating a strong relationship between FFQ-derived TDP and the true polyphenol intake. This study shows that the FFQ is an adequate tool not only for measuring dietary polyphenol exposure in nutrition epidemiological studies but also for guiding clinicians in dietary advice and counselling.

Comparative Metabolomics Elucidates Postprandial Metabolic Modifications in Plasma of Obese Individuals with Metabolic Syndrome

Although higher intakes of dairy milk are associated with a lower risk of metabolic syndrome (MetS), the underlying protective mechanism remains unclear. This study investigated the dynamic metabolic profile shift following the ingestion of low-fat milk or an isocaloric volume of rice milk in obese individuals with metabolic syndrome (MetS). In a randomized, double-blind, crossover study, postprandial plasma samples ( n = 266) were collected from 19 MetS participants. Plasma samples were analyzed by a targeted metabolomics platform which specifically detects 117 metabolites from 25 metabolic pathways. The comprehensive time-course metabolic profiling in MetS participants indicated that the postprandial metabolic profiles distinguish low-fat milk and rice milk consumption in a time-dependent manner. Metabolic biomarkers, such as orotate, leucine/isoleucine and adenine, showed significantly different trends in the two test beverages. Bayesian statistics identified 12 metabolites associated with clinical characteristics of postprandial vascular endothelial function, such as flow-mediated dilation (FMD), postprandial plasma markers of oxidative stress and NO status. Furthermore, metabolic pathway analysis based on these metabolite data indicated the potential utility of metabolomics to provide mechanistic insights of dietary interventions to regulate postprandial metabolic excursions.

Nutrition epidemiology of flavan-3-ols: The known unknowns

Nutritional epidemiology has an important role, as it can provide long-term data from large populations and does not rely on surrogate markers for morbidity/mortality. Meaningful interpretation and applications of outcomes from epidemiological studies depend on the accurate assessment of dietary intake, which is currently mainly based on a combination of self-reporting and food composition data. Flavan-3-ols are a group of bioactives (non-essential dietary components with significant impact on health) that is a possible candidate for the development of dietary recommendations. The breadth of data available on their effect on health also provides the basis for investigating the suitability of the methods currently used in nutritional epidemiology to assess the health effects of bioactives. The outcomes of this assessment demonstrate that the limitations of currently used methods make it virtually impossible to estimate intake accurately from self-reported dietary data. This is due to the limitations of self-reporting, especially from food-frequency questionnaires, and the inability of currently used methods to deal with the high variability of food composition. Indeed, the estimated intake of flavan-3-ols, can only be interpreted as a marker of specific dietary patterns, but not as the actual intake amount. The interpretation of results from such studies are fraught with serious limitations, especially for establishing associations between intake and health and the development of dietary recommendations. Alternative assessment not affected by these limitations, such as biomarkers, are required to overcome these limitations. The development of nutritional biomarkers is therefore crucial to investigate the health effect of bioactives.

Nutrition for the ageing brain: Towards evidence for an optimal diet

As people age they become increasingly susceptible to chronic and extremely debilitating brain diseases. The precise cause of the neuronal degeneration underlying these disorders, and indeed normal brain ageing remains however elusive. Considering the limits of existing preventive methods, there is a desire to develop effective and safe strategies. Growing preclinical and clinical research in healthy individuals or at the early stage of cognitive decline has demonstrated the beneficial impact of nutrition on cognitive functions. The present review is the most recent in a series produced by the Nutrition and Mental Performance Task Force under the auspice of the International Life Sciences Institute Europe (ILSI Europe). The latest scientific advances specific to how dietary nutrients and non-nutrient may affect cognitive ageing are presented. Furthermore, several key points related to mechanisms contributing to brain ageing, pathological conditions affecting brain function, and brain biomarkers are also discussed. Overall, findings are inconsistent and fragmented and more research is warranted to determine the underlying mechanisms and to establish dose-response relationships for optimal brain maintenance in different population subgroups. Such approaches are likely to provide the necessary evidence to develop research portfolios that will inform about new dietary recommendations on how to prevent cognitive decline.

Association between Both Total Baseline Urinary and Dietary Polyphenols and Substantial Physical Performance Decline Risk in Older Adults: A 9-year Follow-up of the InCHIANTI Study

IMPORTANCE

The decline in physical performance that occurs in many older subjects is a strong predictor of falls, hospitalization, institutionalization and mortality. Polyphenols are bioactive compounds that may play a preventive role against physical performance decline due to their antioxidant and anti-inflammatory properties.

OBJECTIVE

To investigate the association between total urinary polyphenols (TUP) and total dietary polyphenols (TDP) and substantial physical performance decline over a nine-year period among older subjects.

METHODS

This longitudinal study included 368 participants aged 65 years or older from the InCHIANTI (Invecchiare in Chianti) study, an Italian population-based cohort. TUP and TDP concentrations were assessed at baseline using the Folin-Ciocalteau (F-C) assay and a validated food frequency questionnaire, respectively. Physical performance was objectively measured at baseline and at nine-year follow-up using the Short Physical Performance Battery (SPPB). A substantial decline in physical performance was considered as a decrease of three or more points in the SPPB score.

RESULTS

At the nine-year follow-up assessment, 71 participants had suffered a substantial decline in physical performance. In the fully adjusted logistic regression model, participants in the highest TUP tertile had a lower risk of substantial decline in physical performance than those in the lowest tertile (OR, 0.40; 95% CI, 0.17-0.93; P trend=0.033). However, no significant association between TDP intake and physical performance decline was observed.

CONCLUSION

This study shows that high TUP concentrations, a biomarker of polyphenol-rich exposure, were associated with lower risk of substantial decline in physical performance in community-dwelling older subjects over a nine-year period. These results suggest that a polyphenol-rich diet may play a role in protecting against physical performance decline in older people.

Resveratrol metabolite profiling in clinical nutrition research--from diet to uncovering disease risk biomarkers: epidemiological evidence

Resveratrol is a bioactive plant compound that has drawn scientific and media attention owing to its protective effects against a wide variety of illnesses, including cardiovascular diseases and cancer. In the last two decades, a plethora of preclinical studies have shown these beneficial effects, and some of them have been supported by clinical trials. However, there are few epidemiological studies assessing these relationships, showing mostly inconsistent results among them. This could be partially due to the difficulty of accurately estimating dietary resveratrol exposure. The development of Phenol-Explorer, a database containing resveratrol food-composition data, will facilitate the estimation of resveratrol intake. Moreover, the discovery and validation of a nutritional biomarker of this exposure, urinary resveratrol metabolite profile, will allow a more accurate assessment of dietary resveratrol exposure. Few epidemiological studies have assessed the potential health effects of resveratrol. Resveratrol was not associated with total mortality, cancer, or cardiovascular events, but it was associated with an improvement of serum glucose and triglyceride levels and a decrease in heart rate. Together, these findings suggest a potential cardioprotective effect of resveratrol in epidemiological studies, although the evidence is still scarce.

Improving the estimation of flavonoid intake for study of health outcomes

Imprecision in estimating intakes of non-nutrient bioactive compounds such as flavonoids is a challenge in epidemiologic studies of health outcomes. The sources of this imprecision, using flavonoids as an example, include the variability of bioactive compounds in foods due to differences in growing conditions and processing, the challenges in laboratory quantification of flavonoids in foods, the incompleteness of flavonoid food composition tables, and the lack of adequate dietary assessment instruments. Steps to improve databases of bioactive compounds and to increase the accuracy and precision of the estimation of bioactive compound intakes in studies of health benefits and outcomes are suggested.

Low Levels of a Urinary Biomarker of Dietary Polyphenol Are Associated with Substantial Cognitive Decline over a 3-Year Period in Older Adults: The Invecchiare in Chianti Study

OBJECTIVES

To investigate the association between total urinary polyphenols (TUPs) and total dietary polyphenols (TDPs) and cognitive decline in an older population.

DESIGN

The Invecchiare in Chianti (InCHIANTI) study, a cohort study with 3 years of follow-up.

SETTING

Tuscany, Italy.

PARTICIPANTS

Individuals without dementia aged 65 and older (N=652).

MEASUREMENTS

TUP and TDP concentrations were analyzed at baseline using the Folin-Ciocalteu assay and a validated food frequency questionnaire, respectively. Cognition was assessed using the Mini-Mental State Examination (MMSE) and Trail-Making Test (TMT) at baseline and after 3 years of follow-up. Substantial cognitive decline was defined as a reduction in MMSE score of three or more points and an increase of at least 29 seconds on the TMT Part A (TMT-A) and 68 seconds on the TMT Part B (TMT-B) (the worst 10% of the distribution of decline) or as test discontinued because of multiple mistakes on the TMT A and B at follow-up.

RESULTS

Higher TUP levels were associated with lower risk of substantial cognitive decline on the MMSE (odds ratio (OR) comparing extreme tertiles=0.53, 95% confidence interval (CI)=0.34-0.85, P-trend=.008) and on the TMT-A (OR=0.52, 95% CI=0.28-0.96, P-trend=.03), but not on TMT-B in a logistic regression model that adjusted for baseline cognitive score and potential confounding factors. TDP did not affect the development of substantial cognitive decline in either test.

CONCLUSION

High concentrations of polyphenols, a nutritional biomarker of polyphenol intake, were associated with lower risk of substantial cognitive decline in an older population studied over a 3-year period, suggesting a protective effect against cognitive impairment.

Dietary flavonoids and nitrate: effects on nitric oxide and vascular function

Emerging evidence highlights dietary flavonoids and nitrate as candidates that may explain at least part of the cardioprotective effect of a fruit and vegetable diet. Nitric oxide plays a pivotal role in cardiovascular health. Components of a fruit and vegetable diet that are cardioprotective, in part through effects on nitric oxide status, could substantially reduce the cardiovascular risk profile of the general population with increased intake of such a diet. Epidemiological evidence suggests that dietary flavonoids and nitrate have a cardioprotective effect. Clinical trials with flavonoid- and nitrate-rich foods have shown benefits on measures of vascular health. While the molecular mechanisms by which flavonoids and nitrate are cardioprotective are not completely understood, recent evidence suggests both nonspecific and specific effects through nitric oxide pathways. This review presents an overview of nitric oxide and its key role in cardiovascular health and discusses the possible vascular benefits of flavonoids and nitrate, individually and in combination, through effects on nitric oxide status.

Measuring exposure to the polyphenol metabolome in observational epidemiologic studies: current tools and applications and their limits

Much experimental evidence supports a protective role of dietary polyphenols against chronic diseases such as cardiovascular diseases, diabetes, and cancer. However, results from observational epidemiologic studies are still limited and are often inconsistent. This is largely explained by the difficulties encountered in the estimation of exposure to the polyphenol metabolome, which is composed of ~500 polyphenols distributed across a wide variety of foods and characterized by diverse biological properties. Exposure to the polyphenol metabolome in epidemiologic studies can be assessed by the use of detailed dietary questionnaires or the measurement of biomarkers of polyphenol intake. The questionnaire approach has been greatly facilitated by the use of new databases on polyphenol composition but is limited by bias as a result of self-reporting. The use of polyphenol biomarkers holds much promise for objective estimation of polyphenol exposure in future metabolome-wide association studies. These approaches are reviewed and their advantages and limitations discussed by using examples of epidemiologic studies on polyphenols and cancer. The current improvement in these techniques, along with greater emphasis on the intake of individual polyphenols rather than polyphenols considered collectively, will help unravel the role of these major food bioactive constituents in disease prevention.

Novel multimetabolite prediction of walnut consumption by a urinary biomarker model in a free-living population: the PREDIMED study

The beneficial impact of walnuts on human health has been attributed to their unique chemical composition. In order to characterize the dietary walnut fingerprinting, spot urine samples from two sets of 195 (training) and 186 (validation) individuals were analyzed by an HPLC-q-ToF-MS untargeted metabolomics approach, selecting the most discriminating metabolites by multivariate data analysis (VIP ≥ 1.5). Stepwise logistic regression analysis was used to design a multimetabolite prediction biomarker model. The global performance of the model and each included metabolite in it was evaluated by receiver operating characteristic curves, using the area under the curve (AUC) values. Dietary exposure to walnuts was characterized by 18 metabolites, including markers of fatty acid metabolism, ellagitannin-derived microbial compounds, and intermediate metabolites of the tryptophan/serotonin pathway. The predictive model of walnut exposure included at least one compound of each class. The AUC (95% CI) for the combined biomarker model was 93.4% (90.1-96.8%) in the training set and 90.2% (85.9-94.6%) in the validation set. The AUCs for individual metabolites were ≤85%. As far as we know, this is the first study proposing a combination of biomarkers of walnut exposure in a population under free-living conditions, as considered in epidemiological studies examining associations between diet and health outcomes.

Dietary intakes of individual flavanols and flavonols are inversely associated with incident type 2 diabetes in European populations

Dietary flavanols and flavonols, flavonoid subclasses, have been recently associated with a lower risk of type 2 diabetes (T2D) in Europe. Even within the same subclass, flavonoids may differ considerably in bioavailability and bioactivity. We aimed to examine the association between individual flavanol and flavonol intakes and risk of developing T2D across European countries. The European Prospective Investigation into Cancer and Nutrition (EPIC)-InterAct case-cohort study was conducted in 8 European countries across 26 study centers with 340,234 participants contributing 3.99 million person-years of follow-up, among whom 12,403 incident T2D cases were ascertained and a center-stratified subcohort of 16,154 individuals was defined. We estimated flavonoid intake at baseline from validated dietary questionnaires using a database developed from Phenol-Explorer and USDA databases. We used country-specific Prentice-weighted Cox regression models and random-effects meta-analysis methods to estimate HRs. Among the flavanol subclass, we observed significant inverse trends between intakes of all individual flavan-3-ol monomers and risk of T2D in multivariable models (all P-trend < 0.05). We also observed significant trends for the intakes of proanthocyanidin dimers (HR for the highest vs. the lowest quintile: 0.81; 95% CI: 0.71, 0.92; P-trend = 0.003) and trimers (HR: 0.91; 95% CI: 0.80, 1.04; P-trend = 0.07) but not for proanthocyanidins with a greater polymerization degree. Among the flavonol subclass, myricetin (HR: 0.77; 95% CI: 0.64, 0.93; P-trend = 0.001) was associated with a lower incidence of T2D. This large and heterogeneous European study showed inverse associations between all individual flavan-3-ol monomers, proanthocyanidins with a low polymerization degree, and the flavonol myricetin and incident T2D. These results suggest that individual flavonoids have different roles in the etiology of T2D.

The association between dietary flavonoid and lignan intakes and incident type 2 diabetes in European populations: the EPIC-InterAct study

OBJECTIVE

To study the association between dietary flavonoid and lignan intakes, and the risk of development of type 2 diabetes among European populations.

RESEARCH DESIGN AND METHODS

The European Prospective Investigation into Cancer and Nutrition-InterAct case-cohort study included 12,403 incident type 2 diabetes cases and a stratified subcohort of 16,154 participants from among 340,234 participants with 3.99 million person-years of follow-up in eight European countries. At baseline, country-specific validated dietary questionnaires were used. A flavonoid and lignan food composition database was developed from the Phenol-Explorer, the U.K. Food Standards Agency, and the U.S. Department of Agriculture databases. Hazard ratios (HRs) from country-specific Prentice-weighted Cox regression models were pooled using random-effects meta-analysis.

RESULTS

In multivariable models, a trend for an inverse association between total flavonoid intake and type 2 diabetes was observed (HR for the highest vs. the lowest quintile, 0.90 [95% CI 0.77-1.04]; P value trend = 0.040), but not with lignans (HR 0.88 [95% CI 0.72-1.07]; P value trend = 0.119). Among flavonoid subclasses, flavonols (HR 0.81 [95% CI 0.69-0.95]; P value trend = 0.020) and flavanols (HR 0.82 [95% CI 0.68-0.99]; P value trend = 0.012), including flavan-3-ol monomers (HR 0.73 [95% CI 0.57-0.93]; P value trend = 0.029), were associated with a significantly reduced hazard of diabetes.

CONCLUSIONS

Prospective findings in this large European cohort demonstrate inverse associations between flavonoids, particularly flavanols and flavonols, and incident type 2 diabetes. This suggests a potential protective role of eating a diet rich in flavonoids, a dietary pattern based on plant-based foods, in the prevention of type 2 diabetes.

Metabolomics in the identification of biomarkers of dietary intake

Traditional methods for assessing dietary exposure can be unreliable, with under reporting one of the main problems. In an attempt to overcome such problems there is increasing interest in identifying biomarkers of dietary intake to provide a more accurate measurement. Metabolomics is an analytical technique that aims to identify and quantify small metabolites. Recently, there has been an increased interest in the application of metabolomics coupled with statistical analysis for the identification of dietary biomarkers, with a number of putative biomarkers identified. This minireview focuses on metabolomics based approaches and highlights some of the key successes.