Flavonoid-rich apples and nitrate-rich spinach augment nitric oxide status and improve endothelial function in healthy men and women: a randomized controlled trial

Consumption of nitrate-containing vegetables is inversely associated with hypertension in adults: a prospective investigation from the Tehran Lipid and Glucose Study

BACKGROUND

There is growing evidence of the potential properties of nitrate-rich foods against development of hypertension (HTN) and vascular disease. In this study, we investigated the association of nitrate-containing vegetables (NCVs) with risk of HTN after 3 years of follow-up.

METHODS

This prospective study was conducted on 1546 non-hypertensive subjects, aged 20-70 years. Blood pressure was measured at baseline and after 3 years and HTN was defined by the Joint National Committee on prevention, detection, evaluation and treatment of high blood pressure criteria. Dietary intake was collected using a validated semi-quantitative food frequency questionnaire (FFQ). NCVs and high-, medium- and low-NCV subcategories were defined, and the odds of HTN after 3 years according to tertiles of NCV and NCV-category intake were estimated by logistic regression and adjusted for potential variables.

RESULTS

Mean age of participants was 38.0 ± 12.0 years at baseline and 57.0 % were women. Mean dietary intake of energy-adjusted NCV was 298.0 ± 177.3 g/day. After adjustment for total energy intake, fiber, sodium, potassium and processed meat, a significant inverse association was observed between NCV and the risk of HTN in the highest tertile category (odds ratio 0.63, 95 % confidence interval: 0.41-0.98, p for trend = 0.05). There was no significant association of 3 year risk of HTN across tertiles of low nitrate-, medium nitrate- and high-nitrate vegetables.

CONCLUSION

Higher dietary nitrate intake from vegetables sources may have a protective effect against development of HTN.

The mechanisms of action of flavonoids in the brain: Direct versus indirect effects

The projected increase in the incidence of dementia in the population highlights the urgent need for a more comprehensive understanding of how different aspects of lifestyle, in particular exercise and diet, may affect neural function and consequent cognitive performance throughout the life course. In this regard, flavonoids, found in a variety of fruits, vegetables and derived beverages, have been identified as a group of promising bioactive compounds capable of influencing different aspects of brain function, including cerebrovascular blood flow and synaptic plasticity, both resulting in improvements in learning and memory in mammalian species. However, the precise mechanisms by which flavonoids exert these actions are yet to be fully established, although accumulating data indicate an ability to interact with neuronal receptors and kinase signaling pathways which are key to neuronal activation and communication and synaptic strengthening. Alternatively or concurrently, there is also compelling evidence derived from human clinical studies suggesting that flavonoids can positively affect peripheral and cerebrovascular blood flow, which may be an indirect effective mechanism by which dietary flavonoids can impact on brain health and cognition. The current review examines the beneficial effects of flavonoids on both human and animal brain function and attempts to address and link direct and indirect actions of flavonoids and their derivatives within the central nervous system (CNS).

Absence of an effect of high nitrate intake from beetroot juice on blood pressure in treated hypertensive individuals: a randomized controlled trial

BACKGROUND

Dietary nitrate, which is in green leafy vegetables and beetroot, decreases blood pressure through the enterosalivary nitrate-nitrite-nitric oxide pathway in healthy individuals. Whether similar effects would occur in individuals with treated hypertension and, therefore, at increased risk of cardiovascular disease is unclear.

OBJECTIVE

We assessed whether increased dietary nitrate intake by using beetroot juice for 1 wk lowers blood pressure in treated hypertensive men and women.

DESIGN

Participants (n = 27) were recruited to a randomized, placebo-controlled, double-blind crossover trial. The effect of 1-wk intake of nitrate-rich beetroot juice was compared with 1-wk intake of nitrate-depleted beetroot juice (placebo). The primary outcome was blood pressure assessed by measuring home blood pressure during the intervention and 24-h ambulatory blood pressure on day 7 of the intervention. Other outcomes included nitrate metabolism assessed by measuring nitrate and nitrite in plasma, saliva, and urine.

RESULTS

Relative to the placebo, 1-wk intake of nitrate-rich beetroot juice resulted in a 3-fold increase in plasma nitrite and nitrate, a 7-fold increase in salivary nitrite, an 8-fold higher salivary nitrate, and a 4-fold increase in both urinary nitrite and nitrate (P < 0.001). However, no differences in home blood pressure and 24-h ambulatory blood pressure were observed with 1-wk intake of nitrate-rich beetroot juice in comparison with the placebo.

CONCLUSION

An increase in dietary nitrate intake may not be an effective short-term approach to further lower blood pressure in treated hypertensive subjects.

Apples and cardiovascular health--is the gut microbiota a core consideration?

There is now considerable scientific evidence that a diet rich in fruits and vegetables can improve human health and protect against chronic diseases. However, it is not clear whether different fruits and vegetables have distinct beneficial effects. Apples are among the most frequently consumed fruits and a rich source of polyphenols and fiber. A major proportion of the bioactive components in apples, including the high molecular weight polyphenols, escape absorption in the upper gastrointestinal tract and reach the large intestine relatively intact. There, they can be converted by the colonic microbiota to bioavailable and biologically active compounds with systemic effects, in addition to modulating microbial composition. Epidemiological studies have identified associations between frequent apple consumption and reduced risk of chronic diseases such as cardiovascular disease. Human and animal intervention studies demonstrate beneficial effects on lipid metabolism, vascular function and inflammation but only a few studies have attempted to link these mechanistically with the gut microbiota. This review will focus on the reciprocal interaction between apple components and the gut microbiota, the potential link to cardiovascular health and the possible mechanisms of action.

Antibacterial mouthwash blunts oral nitrate reduction and increases blood pressure in treated hypertensive men and women

BACKGROUND

Endothelial nitric oxide (NO) is fundamental to cardiovascular health. Dietary nitrate and nitrate from endothelial derived NO metabolism provides a significant contribution to the circulating NO pool through the nitrate-nitrite-NO pathway. A critical step in this pathway is the reduction of nitrate to nitrite by the oral microbiota. We aimed to assess the effects of antibacterial mouthwash use on markers of nitrate-nitrite-NO metabolism and blood pressure in treated hypertensive men and women.

METHODS

Fifteen treated hypertensive men and women (mean age 65 years) were recruited to a randomized controlled cross-over trial. The effects of 3-day use of antibacterial mouthwash on oral nitrate to nitrite reduction, salivary and plasma nitrate and nitrite, plasma cyclic guanosine monophosphate (cGMP) and systolic and diastolic blood pressure were compared to control (water).

RESULTS

Relative to control, 3-day antibacterial mouthwash use resulted in decreased oral nitrate to nitrite reduction (P = 0.02), decreased salivary nitrite (P = 0.01) and increased salivary nitrate (P < 0.001), and there was a trend toward a decrease in plasma nitrite concentration (P = 0.09). Use of antibacterial mouthwash over 3 days also resulted in higher systolic blood pressure (2.3mm Hg; 95% CI: 0.5, 4.0; P = 0.01), but not diastolic blood pressure (P = 0.4) or plasma cGMP (P = 0.7), relative to control.

CONCLUSIONS

Interruption of the nitrate-nitrite-NO pathway through the use of antibacterial mouthwash was paralleled by a small elevation of systolic blood pressure in treated hypertensive men and women.

Flavonoid intake and all-cause mortality

BACKGROUND

Flavonoids are bioactive compounds found in foods such as tea, chocolate, red wine, fruit, and vegetables. Higher intakes of specific flavonoids and flavonoid-rich foods have been linked to reduced mortality from specific vascular diseases and cancers. However, the importance of flavonoids in preventing all-cause mortality remains uncertain.

OBJECTIVE

The objective was to explore the association between flavonoid intake and risk of 5-y mortality from all causes by using 2 comprehensive food composition databases to assess flavonoid intake.

DESIGN

The study population included 1063 randomly selected women aged >75 y. All-cause, cancer, and cardiovascular mortalities were assessed over 5 y of follow-up through the Western Australia Data Linkage System. Two estimates of flavonoid intake (total flavonoidUSDA and total flavonoidPE) were determined by using food composition data from the USDA and the Phenol-Explorer (PE) databases, respectively.

RESULTS

During the 5-y follow-up period, 129 (12%) deaths were documented. Participants with high total flavonoid intake were at lower risk [multivariate-adjusted HR (95% CI)] of 5-y all-cause mortality than those with low total flavonoid consumption [total flavonoidUSDA: 0.37 (0.22, 0.58); total flavonoidPE: 0.36 (0.22, 0.60)]. Similar beneficial relations were observed for both cardiovascular disease mortality [total flavonoidUSDA: 0.34 (0.17, 0.69); flavonoidPE: 0.32 (0.16, 0.61)] and cancer mortality [total flavonoidUSDA: 0.25 (0.10, 0.62); flavonoidPE: 0.26 (0.11, 0.62)].

CONCLUSIONS

Using the most comprehensive flavonoid databases, we provide evidence that high consumption of flavonoids is associated with reduced risk of mortality in older women. The benefits of flavonoids may extend to the etiology of cancer and cardiovascular disease.

Modulation of nitric oxide by flavonoids

One of the main mechanisms by which dietary flavonoids are thought to influence cardiovascular disease is via protection of the bioactivity of the endothelium-derived nitric oxide (NO). Additionally, flavonoids may also interfere with the signalling cascades of inflammation and prevent overproduction of NO and its deleterious consequences in shock and ischemia-reperfusion injury. In the present paper we review the evidence of the effects of flavonoids on NO. Flavonoids exert complex actions on the synthesis and bioavailability of NO which may result both in enhanced or decreased NO levels: (1) in cell free systems, several flavonoids may scavenge NO via its pro-oxidant properties by increasing superoxide. However, under conditions of oxidative stress, flavonoids may also protect NO from superoxide-driven inactivation. (2) In intact healthy tissues, some flavonoids increase eNOS activity in endothelial cells. Paradoxically this effect involves a pro-oxidant effect which results in Ca(2+)-dependent activation of eNOS. As inhibitors of PI3K, flavonoids may potentially inhibit the PI3K/Akt-dependent activation of eNOS. (3) Under conditions of inflammation and oxidative stress, flavonoids may prevent the inflammatory signalling cascades via inhibition of NFκB and thereby downregulate iNOS. On the other hand, they also prevent the overexpression of ROS generating enzymes, reducing superoxide and peroxynitrite levels, and hence preventing superoxide-induced NO inactivation and eNOS uncoupling. Therefore, the final effect of flavonoids on NO levels will depend on the flavonoid structure and the concentrations used, on the cell type under study and particularly on the presence of inflammatory/oxidative conditions.

A shortcut to wide-ranging biological actions of dietary polyphenols: modulation of the nitrate-nitrite-nitric oxide pathway in the gut

Dietary polyphenols are complex, natural compounds with recognized health benefits. Initially attractive to the biomedical area due to their in vitro antioxidant properties, the biological implications of polyphenols are now known to be far from their acute ability to scavenge free radicals but rather to modulate redox signaling pathways. Actually, it is now recognized that dietary polyphenols are extensively metabolized in vivo and that the chemical, biophysical and biological properties of their metabolites are, in most cases, quite different from the ones of the parent molecules. Hence, the study of the metabolic, absorptive and signaling pathways of both phenolics and derivatives has become a major issue. In this paper we propose a short-cut for the systemic effects of polyphenols in connection with nitric oxide (˙NO) biology. This free radical is a ubiquitous signaling molecule with pivotal functions in vivo. It is produced through an enzymatic pathway and also through the reduction of dietary nitrate and nitrite in the human stomach. At acidic gastric pH, dietary polyphenols, in the form they are conveyed in foods and at high concentration, not only promote nitrite reduction to ˙NO but also embark in a complex network of chemical reactions to produce higher nitrogen oxides with signaling functions, namely by inducing post-translational modifications. Modified endogenous molecules, such as nitrated proteins and lipids, acquire important physiological functions. Thus, local and systemic effects of ˙NO such as modulation of vascular tone, mucus production in the gut and protection against ischemia-reperfusion injury are, in this sense, triggered by dietary polyphenols. Evidence to support the signaling and biological effects of polyphenols by modulation of the nitrate-nitrite-NO pathway will be herein provided and discussed. General actions of polyphenols encompassing absorption and metabolism in the intestine/liver are short-cut via the production of diffusible species in the stomach that have not only a local but also a general impact.

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.

Short-term effects of a high nitrate diet on nitrate metabolism in healthy individuals

Dietary nitrate, through the enterosalivary nitrate-nitrite-NO pathway, can improve blood pressure and arterial stiffness. How long systemic nitrate and nitrite remain elevated following cessation of high nitrate intake is unknown. In 19 healthy men and women, the time for salivary and plasma nitrate and nitrite to return to baseline after 7 days increased nitrate intake from green leafy vegetables was determined. Salivary and plasma nitrate and nitrite was measured at baseline [D0], end of high nitrate diet [D7], day 9 [+2D], day 14 [+7D] and day 21 [+14D]. Urinary nitrite and nitrate was assessed at D7 and +14D. Increased dietary nitrate for 7 days resulted in a more than fourfold increase in saliva and plasma nitrate and nitrite (p < 0.001) measured at [D7]. At [+2D] plasma nitrite and nitrate had returned to baseline while saliva nitrate and nitrite were more than 1.5 times higher than at baseline levels. By [+7D] all metabolites had returned to baseline levels. The pattern of response was similar between men and women. Urinary nitrate and nitrate was sevenfold higher at D7 compared to +14D. These results suggest that daily ingestion of nitrate may be required to maintain the physiological changes associated with high nitrate intake.

Interactions between cocoa flavanols and inorganic nitrate: additive effects on endothelial function at achievable dietary amounts

Dietary intervention studies have shown that flavanols and inorganic nitrate can improve vascular function, suggesting that these two bioactives may be responsible for beneficial health effects of diets rich in fruits and vegetables. We aimed to study interactions between cocoa flavanols (CF) and nitrate, focusing on absorption, bioavailability, excretion, and efficacy to increase endothelial function. In a double-blind randomized, dose-response crossover study, flow-mediated dilation (FMD) was measured in 15 healthy subjects before and at 1, 2, 3, and 4 h after consumption of CF (1.4-10.9 mg/kg bw) or nitrate (0.1-10 mg/kg bw). To study flavanol-nitrate interactions, an additional intervention trial was performed with nitrate and CF taken in sequence at low and high amounts. FMD was measured before (0 h) and at 1h after ingestion of nitrate (3 or 8.5 mg/kg bw) or water. Then subjects received a CF drink (2.7 or 10.9 mg/kg bw) or a micro- and macronutrient-matched CF-free drink. FMD was measured at 1, 2, and 4 h thereafter. Blood and urine samples were collected and assessed for CF and nitric oxide (NO) metabolites with HPLC and gas-phase reductive chemiluminescence. Finally, intragastric formation of NO after CF and nitrate consumption was investigated. Both CF and nitrate induced similar intake-dependent increases in FMD. Maximal values were achieved at 1 h postingestion and gradually decreased to reach baseline values at 4 h. These effects were additive at low intake levels, whereas CF did not further increase FMD after high nitrate intake. Nitrate did not affect flavanol absorption, bioavailability, or excretion, but CF enhanced nitrate-related gastric NO formation and attenuated the increase in plasma nitrite after nitrate intake. Both flavanols and inorganic nitrate can improve endothelial function in healthy subjects at intake amounts that are achievable with a normal diet. Even low dietary intake of these bioactives may exert relevant effects on endothelial function when ingested together.

A systematic review of vascular and endothelial function: effects of fruit, vegetable and potassium intake

AIM

To review the relationships between: 1) Potassium and endothelial function; 2) Fruits and vegetables and endothelial function; 3) Potassium and other measures of vascular function; 4) Fruits and vegetables and other measures of vascular function.

DATA SYNTHESIS

An electronic search for intervention trials investigating the effect of potassium, fruits and vegetables on vascular function was performed in MEDLINE, EMBASE and the Cochrane Library. Potassium appears to improve endothelial function with a dose of >40 mmol/d, however the mechanisms for this effect remain unclear. Potassium may improve measures of vascular function however this effect may be dependent on the effect of potassium on blood pressure. The effect of fruit and vegetables on endothelial function independent of confounding variables is less clear. Increased fruit and vegetable intake may improve vascular function only in high risk populations.

CONCLUSION

Increasing dietary potassium appears to improve vascular function but the effect of increasing fruit and vegetable intake per se on vascular function is less clear.

Quercetin and related polyphenols: new insights and implications for their bioactivity and bioavailability

The physiological functions and mechanisms of action of quercetin and its related polyphenols are highlighted, including their effects on brain, blood vessels, muscle, and intestinal microflora.

The acute effect of flavonoid-rich apples and nitrate-rich spinach on cognitive performance and mood in healthy men and women

Flavonoids and nitrate in a fruit and vegetable diet may be protective against cardiovascular disease and cognitive decline through effects on nitric oxide (NO) status. The circulating NO pool is increased via distinct pathways by dietary flavonoids and nitrate. Our aim was to investigate the acute effects of apples, rich in flavonoids, and spinach, rich in nitrate, independently and in combination on NO status, cognitive function and mood in a randomised, controlled, cross-over trial with healthy men and women (n = 30). The acute effects of four energy-matched treatments (control, apple, spinach and apple + spinach) were compared. Endpoints included plasma nitric oxide status (determined by measuring S-nitrosothiols + other nitroso species (RXNO)), plasma nitrate and nitrite, salivary nitrate and nitrite, urinary nitrate and nitrite as well as cognitive function (determined using the Cognitive Drug Research (CDR) computerized cognitive assessment battery) and mood. Relative to control, all treatments resulted in higher plasma RXNO. A significant increase in plasma nitrate and nitrite, salivary nitrate and nitrite as well as urinary nitrate and nitrite was observed with spinach and apple + spinach compared to control. No significant effect was observed on cognitive function or mood. In conclusion, flavonoid-rich apples and nitrate-rich spinach augmented NO status acutely with no concomitant improvements or deterioration in cognitive function and mood.

Effect of tea theaflavins and catechins on microvascular function

Beneficial effects of flavonoid-rich black and green tea on macrocirculation have been well established. Theaflavins are unique to black tea as they are formed from catechins during the enzymatic oxidation of tea leaves. The study was performed to gain more insight into the effects of theaflavins on microcirculation and to compare effects with another important flavonoid class, the green tea derived catechins, which have been reported to improve vascular function. Twenty-four healthy subjects were included in a double-blind, placebo-controlled, randomised, cross-over study. On six different days, subjects received capsules with a single dose of catechins (500 mg), four varying doses of theaflavins (100 to 500 mg) or placebo. Microcirculation was assessed after each treatment by Pulse Amplitude Tonometry (EndoPAT) at baseline and 2, 4 and 6 h after test product intake. The EndoPAT reactive hyperemia response was improved by 500 mg catechins (reactive hyperemia index (RHI): 0.2; p = 0.04) and by 500 mg theaflavins (RHI: 0.19; p = 0.06) compared to placebo. Also, 300 mg theaflavins increased the RHI (0.28; p = 0.02), but no effects were observed at lower doses. The study suggests moderate effects of single doses of catechins and theaflavins on peripheral microcirculation.

Short-term effects of nitrate-rich green leafy vegetables on blood pressure and arterial stiffness in individuals with high-normal blood pressure

Evidence for a beneficial effect of dietary nitrate, through the nitrate-nitrite-NO pathway, on measures of cardiovascular function in healthy individuals is accumulating. It is less clear whether increased dietary nitrate intake from green leafy vegetables would have similar beneficial vascular effects in those at increased risk of developing hypertension. Our aim was to assess the effects of short-term regular consumption of increased nitrate from green leafy vegetables on blood pressure and arterial stiffness in individuals with high-normal blood pressure. Thirty-eight men and women ages 30-70 years with systolic blood pressure 120 to 139 mm Hg were recruited to a randomized controlled crossover trial. The effects of a 7-day high-nitrate diet intervention (increased nitrate intake by at least 300 mg/day from green leafy vegetables) were compared to a 7-day low-nitrate diet intervention. Outcome measures included pre- and postintervention salivary and plasma nitrate and nitrite concentrations; ambulatory, home, and office blood pressure; augmentation index; and carotid-femoral pulse wave velocity. The high-nitrate diet intervention resulted in at least a fourfold increase in salivary and plasma nitrate and nitrite (P<0.001). Ambulatory, home, and office blood pressure and arterial stiffness were not different between the high-nitrate diet and the low-nitrate diet. Increasing dietary nitrate intake in those with high-normal blood pressure and at increased risk of hypertension may not be an effective short-term strategy to lower blood pressure.

Acute dietary nitrate supplementation does not augment submaximal forearm exercise hyperemia in healthy young men

Despite the popularity of dietary nitrate supplementation and the growing evidence base of its potential ergogenic and vascular health benefits, there is no direct information about its effects on exercising limb blood flow in humans. We hypothesized that acute dietary nitrate supplementation from beetroot juice would augment the increases in forearm blood flow, as well as the progressive dilation of the brachial artery, during graded handgrip exercise in healthy young men. In a randomized, double-blind, placebo-controlled crossover study, 12 young (22 ± 2 years) healthy men consumed a beetroot juice (140 mL Beet-It Sport, James White Juice Company) that provided 12.9 mmol (0.8 g) of nitrate or placebo (nitrate-depleted Beet-It Sport) on 2 study visits. At 3 h postconsumption, brachial artery diameter, flow, and blood velocity were measured (Doppler ultrasound) at rest and during 6 exercise intensities. Nitrate supplementation raised plasma nitrate (19.5-fold) and nitrite (1.6-fold) concentrations, and lowered resting arterial pulse wave velocity (PWV) versus placebo (all p < 0.05), indicating absorption, conversion, and a biological effect of this supplement. The supplement-associated lowering of PWV was also negatively correlated with plasma nitrite (r = -0.72, p = 0.0127). Despite these systemic effects, nitrate supplementation had no effect on brachial artery diameter, flow, or shear rates at rest (all p ≥ 0.28) or during any exercise workload (all p ≥ 0.18). These findings suggest that acute dietary nitrate supplementation favorably modifies arterial PWV, but does not augment blood flow or brachial artery vasodilation during nonfatiguing forearm exercise in healthy young men.

Pharmacology and therapeutic role of inorganic nitrite and nitrate in vasodilatation

Nitrite has emerged as an important bioactive molecule that can be biotransformed to nitric oxide (NO) related metabolites in normoxia and reduced to NO under hypoxic and acidic conditions to exert vasodilatory effects and confer a variety of other benefits to the cardiovascular system. Abundant research is currently underway to understand the mechanisms involved and define the role of nitrite in health and disease. In this review we discuss the impact of nitrite and dietary nitrate on vascular function and the potential therapeutic role of nitrite in acute heart failure.

Fruit and vegetable intake and risk of wheezing and asthma: a systematic review and meta-analysis

Major bibliographic databases were searched for studies examining the relationship between fruit and vegetable consumption and the risk of wheezing and asthma. Random-effects models were used to pool study results. Subgroup analyses were conducted by fruit and vegetable categories, study design, and age group. Twelve cohorts, 4 population-based case-control studies, and 26 cross-sectional studies published between January 1990 and July 2013 were identified. For the meta-analysis of adults and children, the relative risk (RR) and confidence intervals (CI) when comparing the highest intake group with the lowest intake group were 0.78 (95%CI, 0.70-0.87) for fruit and 0.86 (95%CI, 0.75-0.98) for vegetables. High intake of fruit and vegetables (RR = 0.76; 95%CI, 0.68-0.86 and RR = 0.83; 95%CI, 0.72-0.96) reduced the risk of childhood wheezing. Total intake of fruit and vegetables had a negative association with risk of asthma in adults and children (RR = 0.54; 95%CI, 0.41-0.69). Consuming fruit and vegetables during pregnancy had no association with the risk of asthma in offspring. High intake of fruit and vegetables may reduce the risk of asthma and wheezing in adults and children.

Flavonoids from fruit and vegetables: a focus on cardiovascular risk factors

Epidemiological studies suggest that high intakes of dietary flavonoids are associated with decreased cardiovascular disease mortality and risk factors. Less is known about the cardioprotective effects of flavonoids from fruit and vegetables. This review summarizes data from studies which examine the effects of commonly consumed fruit and vegetables on cardiovascular disease risk biomarkers in healthy volunteers or at-risk individuals. Although flavonoids from apples, berries, and onions appear to impact positively on blood pressure, vascular function, and serum lipid levels, further research is required to find out the optimal quantity and food matrix for conferring substantial clinical benefit. The benefits from citrus flavonoids are still inconclusive. Further robust, longer-term dietary intervention studies, with the inclusion of placebo or control arms, are required to improve the credibility of the findings and confirm current observations. An improved understanding of the impact of flavonoids from fruit and vegetables can help one make discerning food choices for optimal cardiovascular health.

Inorganic nitrite supplementation for healthy arterial aging

Aging is the major risk factor for cardiovascular diseases (CVD). This is attributable primarily to adverse changes in arteries, notably, increases in large elastic artery stiffness and endothelial dysfunction mediated by inadequate concentrations of the vascular-protective molecule, nitric oxide (NO), and higher levels of oxidative stress and inflammation. Inorganic nitrite is a promising precursor molecule for augmenting circulating and tissue NO bioavailability because it requires only a one-step reduction to NO. Nitrite also acts as an independent signaling molecule, exerting many of the effects previously attributed to NO. Results of recent studies indicate that nitrite may be effective in the treatment of vascular aging. In old mice, short-term oral sodium nitrite supplementation reduces aortic pulse wave velocity, the gold-standard measure of large elastic artery stiffness, and ameliorates endothelial dysfunction, as indicated by normalization of NO-mediated endothelium-dependent dilation. These improvements in age-related vascular dysfunction with nitrite are mediated by reductions in oxidative stress and inflammation, and may be linked to increases in mitochondrial biogenesis and health. Increasing nitrite levels via dietary intake of nitrate appears to have similarly beneficial effects in many of the same physiological and clinical settings. Several clinical trials are being performed to determine the broad therapeutic potential of increasing nitrite bioavailability on human health and disease, including studies related to vascular aging. In summary, inorganic nitrite, as well as dietary nitrate supplementation, represents a promising therapy for treatment of arterial aging and prevention of age-associated CVD in humans.

Green coffee polyphenols do not attenuate features of the metabolic syndrome and improve endothelial function in mice fed a high fat diet

We have investigated the effects of the major polyphenol in coffee, chlorogenic acid (CGA), on obesity, glucose intolerance, insulin resistance, systemic oxidative stress and endothelial dysfunction in a mouse model of the metabolic syndrome. Thirty C57BL6 mice were randomly divided into (n=10/group) (i) normal diet (ND), (ii) high fat diet (HFD), or (iii) high fat diet supplemented with 0.5% w/w green coffee bean extract (GCE) rich in chlorogenic acid (HFD+GCE). The high fat diet consisted of 28% fat and all animals were maintained on their diets for 12 weeks. The mice fed a HFD and HFD+GCE displayed symptoms of the metabolic syndrome compared to their normal fed counterparts, although no endothelial dysfunction was detected in the abdominal aortas after 12 weeks. GCE did not attenuate HFD-induced obesity, glucose intolerance, insulin resistance or systemic oxidative stress. Furthermore, GCE did not protect against ex vivo oxidant (hypochlorous acid)-induced endothelial dysfunction.

Dietary quercetin attenuates oxidant-induced endothelial dysfunction and atherosclerosis in apolipoprotein E knockout mice fed a high-fat diet: a critical role for heme oxygenase-1

Several lines of evidence indicate that quercetin, a polyphenol derived in the diet from fruit and vegetables, contributes to cardiovascular health. We aimed to investigate the effects of dietary quercetin on endothelial function and atherosclerosis in mice fed a high-fat diet. Wild-type C57BL/6 (WT) and apolipoprotein E gene knockout (ApoE(-/-)) mice were fed: (i) a high-fat diet (HFD) or (ii) a HFD supplemented with 0.05% w/w quercetin (HFD+Q), for 14 weeks. Compared with animals fed HFD, HFD+Q attenuated atherosclerosis in ApoE(-/-) mice. Treatment with the HFD+Q significantly improved endothelium-dependent relaxation of aortic rings isolated from WT but not ApoE(-/-) mice and attenuated hypochlorous acid-induced endothelial dysfunction in aortic rings of both WT and ApoE(-/-) mice. Mechanistic studies revealed that HFD+Q significantly improved plasma F2-isoprostanes, 24h urinary nitrite, and endothelial nitric oxide synthase activity, and increased heme oxygenase-1 (HO-1) protein expression in the aortas of both WT and ApoE(-/-) mice (P<0.05). HFD+Q also resulted in small changes in plasma cholesterol (P<0.05 in WT) and plasma triacylglycerols (P<0.05 in ApoE (-/-)mice). In a separate experiment, quercetin did not protect against hypochlorite-induced endothelial dysfunction in arteries obtained from heterozygous HO-1 gene knockout mice with low expression of HO-1 protein. Quercetin protects mice fed a HFD against oxidant-induced endothelial dysfunction and ApoE(-/-) mice against atherosclerosis. These effects are associated with improvements in nitric oxide bioavailability and are critically related to arterial induction of HO-1.

The effects of dietary nitrate on blood pressure and endothelial function: a review of human intervention studies

Evidence has accumulated in recent years that suggests that nitrate from the diet, particularly vegetables, is capable of producing bioactive NO in the vasculature, following bioconversion to nitrite by oral bacteria. The aim of the present review was to consider the current body of evidence for potential beneficial effects of dietary nitrate on blood pressure and endothelial function, with emphasis on evidence from acute and chronic human intervention studies. The studies to date suggest that dietary nitrate acutely lowers blood pressure in healthy humans. An inverse relationship was seen between dose of nitrate consumed and corresponding systolic blood pressure reduction, with doses of nitrate as low as 3 mmol of nitrate reducing systolic blood pressure by 3 mmHg. Moreover, the current studies provide some promising evidence on the beneficial effects of dietary nitrate on endothelial function. In vitro studies suggest a number of potential mechanisms by which dietary nitrate and its sequential reduction to NO may reduce blood pressure and improve endothelial function, such as: acting as a substrate for endothelial NO synthase; increasing vasodilation; inhibiting mitochondrial reactive oxygen species production and platelet aggregation. In conclusion, the evidence for beneficial effects of dietary nitrate on blood pressure and endothelial function is promising. Further long-term randomised controlled human intervention studies assessing the potential effects of dietary nitrate on blood pressure and endothelial function are needed, particularly in individuals with hypertension and at risk of CVD.

Beetroot juice improves in overweight and slightly obese men postprandial endothelial function after consumption of a mixed meal

BACKGROUND

Through effects on nitric oxide (NO) bioavailability, endothelial function is improved after the intake of beetroot juice-which is rich in inorganic nitrate-, but decreased after the intake of a meal.

OBJECTIVE

The objective of this study was to examine if beetroot juice could counteract the impairment of endothelial function associated with the ingestion of a mixed meal.

METHODS

Twenty healthy overweight and slightly obese men with a BMI between 28 and 35 kg/m(2) received in random order a mixed meal providing 56.6 g of fat with beetroot juice or a control drink. The beetroot juice (140 mL) provided approximately 500 mg dietary nitrate. Flow-mediated dilation (FMD) of the brachial artery was measured before and 2 h after meal consumption. Blood was sampled at regular intervals.

RESULTS

Postprandial changes in serum triacylglycerol (TAG) (P = 0.69), plasma glucose (P = 0.84) and insulin (P = 0.67) concentrations were comparable between the meals. After consumption of beetroot juice, the postprandial impairment in FMD following a standardized mixed meal was improved (P = 0.030) compared with the control drink (-0.37 ± 2.92% versus -1.56 ± 2.90%). Following beetroot juice consumption, plasma concentrations of the circulating NO pool were higher at T60, T120, and T240 (P < 0.001 at all time points).

CONCLUSION

In healthy overweight and slightly obese men a single dose of beetroot juice attenuates the postprandial impairment of FMD following a mixed meal, possibly through increases in plasma NO concentrations.

Acute ingestion of beetroot bread increases endothelium-independent vasodilation and lowers diastolic blood pressure in healthy men: a randomized controlled trial

Dietary nitrate, from beetroot, has been reported to lower blood pressure (BP) by the sequential reduction of nitrate to nitrite and further to NO in the circulation. However, the impact of beetroot on microvascular vasodilation and arterial stiffness is unknown. In addition, beetroot is consumed by only 4.5% of the UK population, whereas bread is a staple component of the diet. Thus, we investigated the acute effects of beetroot bread (BB) on microvascular vasodilation, arterial stiffness, and BP in healthy participants. Twenty-three healthy men received 200 g bread containing 100 g beetroot (1.1 mmol nitrate) or 200 g control white bread (CB; 0 g beetroot, 0.01 mmol nitrate) in an acute, randomized, open-label, controlled crossover trial. The primary outcome was postprandial microvascular vasodilation measured by laser Doppler iontophoresis and the secondary outcomes were arterial stiffness measured by Pulse Wave Analysis and Velocity and ambulatory BP measured at regular intervals for a total period of 6 h. Plasma nitrate and nitrite were measured at regular intervals for a total period of 7 h. The incremental area under the curve (0-6 h after ingestion of bread) for endothelium-independent vasodilation was greater (P = 0.017) and lower for diastolic BP (DBP; P = 0.032) but not systolic (P = 0.99) BP after BB compared with CB. These effects occurred in conjunction with increases in plasma and urinary nitrate (P < 0.0001) and nitrite (P < 0.001). BB acutely increased endothelium-independent vasodilation and decreased DBP. Therefore, enriching bread with beetroot may be a suitable vehicle to increase intakes of cardioprotective beetroot in the diet and may provide new therapeutic perspectives in the management of hypertension.

Vascular effects of dietary nitrate (as found in green leafy vegetables and beetroot) via the nitrate-nitrite-nitric oxide pathway

The discovery that dietary (inorganic) nitrate has important vascular effects came from the relatively recent realization of the 'nitrate-nitrite-nitric oxide (NO) pathway'. Dietary nitrate has been demonstrated to have a range of beneficial vascular effects, including reducing blood pressure, inhibiting platelet aggregation, preserving or improving endothelial dysfunction, enhancing exercise performance in healthy individuals and patients with peripheral arterial disease. Pre-clinical studies with nitrate or nitrite also show the potential to protect against ischaemia-reperfusion injury and reduce arterial stiffness, inflammation and intimal thickness. However, there is a need for good evidence for hard endpoints beyond epidemiological studies. Whilst these suggest reduction in cardiovascular risk with diets high in nitrate-rich vegetables (such as a Mediterranean diet), others have suggested possible small positive and negative associations with dietary nitrate and cancer, but these remain unproven. Interactions with other nutrients, such as vitamin C, polyphenols and fatty acids may enhance or inhibit these effects. In order to provide simple guidance on nitrate intake from different vegetables, we have developed the Nitrate 'Veg-Table' with 'Nitrate Units' [each unit being 1 mmol of nitrate (62 mg)] to achieve a nitrate intake that is likely to be sufficient to derive benefit, but also to minimize the risk of potential side effects from excessive ingestion, given the current available evidence. The lack of data concerning the long term effects of dietary nitrate is a limitation, and this will need to be addressed in future trials.

Associations of proanthocyanidin intake with renal function and clinical outcomes in elderly women

Background

Progression to chronic renal failure involves accelerated atherosclerosis and vascular calcification. Oxidative stress and endothelial dysfunction play a role in renal failure pathophysiology. In addition to improving vascular health and function, proanthocyanidins have been shown to exert renoprotective effects in animal models. Thus we hypothesize that proanthocyanidins may contribute to the maintenance of healthy renal function.

Objective

Determine the association of habitual proanthocyanidin intake with renal function and the risk of clinical renal outcomes in a population of elderly women.

Design

948 women aged over 75 y, free of prevalent renal disease at baseline, were randomly selected from ambulant Caucasian women. Proanthocyanidin consumption was determined using a validated food frequency questionnaire and the United States Department of Agriculture proanthocyanidin food content database. Fasting serum cystatin C and creatinine were assessed at baseline. Renal failure hospitalisations and deaths were assessed over 5 years of follow-up through the Western Australia Data Linkage System.

Results

Compared to participants with low consumption, participants in the highest tertile of proanthocyanidin intake had a 9% lower cystatin C concentration (P<0.001). High proanthocyanidin consumers were at 50% lower risk of moderate chronic kidney insufficiency, and 65% lower risk of experiencing a 5-year renal disease event (P<0.05). These relationships remained significant following adjustment for renal disease risk factors and diet-related potential confounders.

Conclusion

Increased consumption of proanthocyanidins was associated with better renal function and substantially reduced renal associated events, which has been supported by mechanistic and animal model data. Proanthocyanidin intake should be further examined as a dietary contributor to better renal health.

Garlic intake is an independent predictor of endothelial function in patients with ischemic stroke

OBJECTIVES

To investigate the effects of garlic on endothelial function in patients with ischemic stroke (ISS).

DESIGN

Cross-sectional study.

PARTICIPANTS

125 Chinese patients with prior ISS due to athero-thrombotic disease were recruited from the outpatient clinics during July 2005 to December 2006.

MEASUREMENTS

Daily allium vegetable intake (including garlic, onions, Chinese chives and shallots) was ascertained by means of a validated food frequency questionnaire for Chinese and brachial artery flow-mediated dilatation (FMD) was measured using high-resolution ultrasound in all subjects.

RESULTS

The mean age of the study population was 65.9±11.1 years and 69% were males. Mean allium vegetable intake and garlic intake of the study population was 7.5±12.7g/day and 2.9±8.8g/day respectively. Their mean FMD was 2.6±2.3%. Daily intake of total allium vegetable (r=0.36, P<0.01) and garlic (r=0.34, P<0.01) significantly correlated with FMD. Using the median daily allium intake as cut-off (3.37g/day), patients with a low allium intake <3.37g/day was noted to have a lower FMD compared to those with a normal allium intake (2.1±2.1% versus 3.0±2.4%, P<0.05). After adjusting for confounding factors, multi-variate analysis identified that daily allium vegetable (B=0.05, 95% confidence interval: 0.02, 0.09, P<0.01) and garlic (B=0.07, 95% confidence interval: 0.02, 0.12, P<0.01) intake, but not onions, Chinese chives and shallots were independent predictors for changes in FMD in patients with ISS.

CONCLUSIONS

Daily garlic intake is an independent predictor of endothelial function in patients with ISS and may play a role in the secondary prevention of atherosclerotic events.

Supplementation of a high-fat diet with chlorogenic acid is associated with insulin resistance and hepatic lipid accumulation in mice

The increasing prevalence of the metabolic syndrome requires a greater need for therapeutic and prevention strategies. Higher coffee consumption is consistently associated with a lower risk of type 2 diabetes in population studies. Dietary polyphenols have been linked to benefits on several features of the metabolic syndrome. Chlorogenic acid (CGA), a major component of coffee, is one of the most consumed polyphenols in the diet. In our study, we conducted a controlled dietary intervention over 12 weeks in male mice. There were three dietary groups: (i) normal diet, (ii) high-fat diet, and (iii) high-fat diet + CGA. We assessed the effect of CGA at a physiologically obtainable dose (1 g/kg of diet) on high-fat-diet-induced obesity, glucose intolerance, insulin resistance, and also fatty acid oxidation and insulin signaling in C57BL/6 male mice. Supplementation of CGA in the high-fat diet did not reduce body weight compared to mice fed the high-fat diet alone (p = 0.32). CGA resulted in increased insulin resistance compared to mice fed a high-fat diet only (p < 0.05). CGA resulted in decreased phosphorylation of AMP-activated protein kinase (AMPK) (p < 0.001) and acetyl carboxylase β (ACCβ), a downstream target of AMPK (p < 0.05), in liver. The liver of mice fed a high-fat diet supplemented with CGA had a higher lipid content (p < 0.05) and more steatosis relative to mice fed a high-fat diet only, indicating impaired fatty acid oxidation. This study suggests that CGA supplementation in a high-fat diet does not protect against features of the metabolic syndrome in diet-induced obese mice.

Tea and non-tea flavonol intakes in relation to atherosclerotic vascular disease mortality in older women

Epidemiological studies have indicated that dietary flavonoids generally, and flavonols specifically, may contribute to cardiovascular health. Tea consumption, which is often the main dietary source of flavonoids and flavonols, is associated with a reduced risk of cardiovascular outcomes. The primary objective of the present study was to explore the association of the habitual intake of flavonols from tea and non-tea sources with the risk of atherosclerotic vascular disease mortality in a population of elderly women. A total of 1063 women, aged over 75 years, were randomly selected from ambulant Caucasian women living in Perth, Western Australia. Flavonoid consumption was assessed using the US Department of Agriculture Flavonoid, Flavone and Proanthocyanidin databases. Atherosclerotic vascular disease mortality was assessed over 5 years of follow-up through the Western Australian Data Linkage System. During the follow-up, sixty-four women died from atherosclerotic vascular disease. Women in the highest compared with the lowest tertile of flavonol intake had a lower risk of atherosclerotic vascular disease death (OR 0·27, 95 % CI 0·13, 0·59; P≤ 0·01 for trend in multivariate-adjusted models). Similar relationships were observed for flavonol intake derived from both tea (OR 0·38, 95 % CI 0·18, 0·79; P< 0·01) and non-tea (OR 0·41, 95 % CI 0·20, 0·85; P= 0·05) sources. Tea was the main contributor to flavonol intake (65 %), and the intakes of flavonols from tea and non-tea sources were not significantly correlated. In conclusion, increased consumption of flavonols was independently associated with a lower risk of atherosclerotic vascular disease mortality. Both tea and non-tea sources of flavonols were independently associated with this benefit.

Bioavailability of epicatechin and effects on nitric oxide metabolites of an apple flavanol-rich extract supplemented beverage compared to a whole apple puree: a randomized, placebo-controlled, crossover trial

SCOPE

Flavanol-rich foods are known to exert beneficial effects on cardiovascular health. The biological effects depend on bioavailability of flavanols which may be influenced by food matrix and dose ingested. We compared the bioavailability and dose-response of epicatechin from whole apple and an epicatechin-rich extract, and the effects on plasma and urinary nitric oxide (NO) metabolites.

METHODS AND RESULTS

In a randomized, placebo-controlled, crossover trial, subjects consumed drinks containing 70 and 140 mg epicatechin from an apple extract and an apple puree containing 70 mg epicatechin. Blood and urine samples were collected for 24 h post ingestion. Maximum plasma concentration, AUC(0-24 h) , absorption and urinary excretion were all significantly higher after ingestion of both epicatechin drinks compared with apple puree (p < 0.05). Time to maximum plasma concentration was significantly later for the puree compared with the drinks (p < 0.01). Epicatechin bioavailability was >2-fold higher after ingestion of the 140 mg epicatechin drink compared to the 70 mg epicatechin drink (p < 0.05). Excretion of NO metabolites was higher for all test products compared with placebo, which was significant for the high dose drink (p = 0.016).

CONCLUSIONS

Oral bioavailability of apple epicatechin increases at higher doses, is reduced by whole apple matrix and has the potential to increase NO bioavailability.

Therapeutic approach in the improvement of endothelial dysfunction: the current state of the art

The endothelium has a central role in the regulation of blood flow through continuous modulation of vascular tone. This is primarily accomplished by balanced release of endothelial relaxing and contractile factors. The healthy endothelial cells are essential for maintenance of vascular homeostasis involving antioxidant, anti-inflammatory, pro-fibrinolytic, anti-adhesive, or anticoagulant effects. Oppositely, endothelial dysfunction is primarily characterized by impaired regulation of vascular tone as a result of reduced endothelial nitric oxide (NO) synthase activity, lack of cofactors for NO synthesis, attenuated NO release, or increased NO degradation. So far, the pharmacological approach in improving/reversal of endothelial dysfunction was shown to be beneficial in clinical trials that have investigated actions of different cardiovascular drugs. The aim of this paper was to summarize some of the latest clinical findings related to therapeutic possibilities for improving endothelial dysfunction in different pathological conditions. In the majority of presented clinical investigations, the assessment of improvement or reversal of endothelial dysfunction was performed through the flow-mediated dilatation measurement, and in some of those endothelial progenitor cells' count was used for the same purpose. Still, given the fast and continuous development of this field, the evidence acquisition included the MEDLINE data base screening and the selection of articles published between 2010 and 2012.

Polyphenol composition of plum selections in relation to total antioxidant capacity

Dietary polyphenols are associated with protection against chronic diseases such as cardiovascular disease. Pharmacological studies show a range of bioactivities and efficacy attributable to specific polyphenols. While many fruits are rich in polyphenols, wide cultivar variation of polyphenol composition is common. Our objective was to determine the composition of major bioactive polyphenols in 29 prevarietal selections of Western Australian plums, and Black Amber as an evaluation in developing breeding tools to develop fruit that may have enhanced health-promoting capacities. Total phenolics were quantified colorimetrically; selected polyphenols were quantified by HPLC; and the total antioxidant capacity (TAC) was measured by the antioxidant inhibition of oxygen radicals (AIOR) assay. Total phenolic concentration was significantly correlated with TAC (R = 0.95, P < 0.01). Neo-chlorogenic acid and quercetin glycosides were found to be the predominant polyphenols (mean 29.9 mg·kg(-1) and 50.7 mg·kg(-1), respectively). No significant correlations were found between the composition of predominant polyphenols in plums and the TAC. We argue that the value of in vitro TAC assays to breeding programs may be limited, and future research should focus on the heritability of known bioactive polyphenols.