Effects of short-term dietary nitrate supplementation on blood pressure, O2 uptake kinetics, and muscle and cognitive function in older adults

A randomised crossover trial of nitrate and breakfast on prefrontal cognitive and haemodynamic response functions

It remains unknown whether dietary nitrate and breakfast may enhance working memory (WM) performance by augmenting physiological mechanisms and subjective psychological well-being. We performed a 3-arm randomised within-subject crossover study, with pretest-posttest comparisons, to test whether nitrate consumption via breakfast with a beetroot juice shot or regular breakfast compared to no breakfast improved WM (measured with n-back tests) and cognitive task-related changes in prefrontal cortical haemodynamic response (oxygenated- and deoxygenated-haemoglobin derived from functional near-infrared spectroscopy). In addition, effects on peripheral vascular function and self-reported psychological factors were assessed. In 60 adolescents (13-15 years old; 66% girls), WM improved in all conditions, with no intervention effects. Intervention effects were seen for oxygenated-haemoglobin changes, such that it increased after the breakfast with a nitrate shot during the WM tests and decreased after the regular breakfast. Thus, different neurophysiological mechanisms may be at play to preserve WM in adolescents depending on their breakfast composition. The trial was registered in the ISRCTN registry (ISRCTN16596056) on 21/02/2022.

Higher plant-derived nitrate intake is associated with lower odds of frailty in a cross-sectional study of community-dwelling older women

PURPOSE

Dietary nitrate intake is inversely related to numerous contributors towards frailty, including cardiovascular disease and poor physical function. Whether these findings extend to frailty remain unknown. We investigated if habitual nitrate intake, derived from plants or animal-based foods, was cross-sectionally associated with frailty in women.

METHODS

Community-dwelling older Australian women (n = 1390, mean age 75.1 ± 2.7 years) completed a validated semi-quantitative food frequency questionnaire (FFQ). Nitrate concentrations in food were obtained from international nitrate databases. We adopted the Rockwood frailty index (FI) of cumulative deficits comprising 33 variables across multiple health domains (scored 0 to 1), which predicts increased hospitalisation and mortality risk. A FI ≥ 0.25 indicated frailty. Cross-sectional associations between nitrate intake (total plant and animal nitrate, separately) and frailty were analysed using multivariable-adjusted logistic regression models (including lifestyle factors), as part of restricted cubic splines.

RESULTS

A non-linear inverse relationship was observed between total plant nitrate intake and frailty. Compared to women with the lowest plant nitrate intake (Quartile [Q]1), women with greater intakes in Q2 (OR 0.69 95%CI 0.56-0.84), Q3 (OR 0.67 95%CI 0.50-0.90) and Q4 (OR 0.66 95%CI 0.45-0.98) had lower odds for frailty. A nadir in the inverse association was observed once intakes reached ~ 64 mg/d (median Q2). No relationship was observed between total animal nitrate and frailty.

CONCLUSION

Community-dwelling older women consuming low amounts of plant-derived nitrate were more likely to present with frailty. Consuming at least one daily serving (~ 75 g) of nitrate-rich green leafy vegetables may be beneficial in preventing frailty.

Do oral and gut microbiota communicate through redox pathways? A novel asset of the nitrate-nitrite-NO pathway

Nitrate may act as a regulator of •NO bioavailability via sequential reduction along the nitrate-nitrite-NO pathway with widespread health benefits, including a eubiotic effect on the oral and gut microbiota. Here, we discuss the molecular mechanisms of microbiota-host communication through redox pathways, via the production of •NO and oxidants by the family of NADPH oxidases, namely hydrogen peroxide (via Duox2), superoxide radical (via Nox1 and Nox2) and peroxynitrite, which leads to downstream activation of stress responses (Nrf2 and NFkB pathways) in the host mucosa. The activation of Nox2 by microbial metabolites is also discussed. Finally, we propose a new perspective in which both oral and gut microbiota communicate through redox pathways, with nitrate as the pivot linking both ecosystems.

Effects of short-term dietary nitrate supplementation on exercise and coronary blood flow responses in patients with peripheral artery disease

Background

Peripheral arterial disease (PAD) is a prevalent vascular disorder characterized by atherosclerotic occlusion of peripheral arteries, resulting in reduced blood flow to the lower extremities and poor walking ability. Older patients with PAD are also at a markedly increased risk of cardiovascular events, including myocardial infarction. Recent evidence indicates that inorganic nitrate supplementation, which is abundant in certain vegetables, augments nitric oxide (NO) bioavailability and may have beneficial effects on walking, blood pressure, and vascular function in patients with PAD.

Objective

We sought to determine if short-term nitrate supplementation (via beetroot juice) improves peak treadmill time and coronary hyperemic responses to plantar flexion exercise relative to placebo (nitrate-depleted juice) in older patients with PAD. The primary endpoints were peak treadmill time and the peak coronary hyperemic response to plantar flexion exercise.

Methods

Eleven PAD patients (52-80 yr.; 9 men/2 women; Fontaine stage II) were randomized (double-blind) to either nitrate-rich (Beet-IT, 0.3 g inorganic nitrate twice/day; BRnitrate) or nitrate-depleted (Beet-IT, 0.04 g inorganic nitrate twice/day, BRplacebo) beetroot juice for 4 to 6 days, followed by a washout of 7 to 14 days before crossing over to the other treatment. Patients completed graded plantar flexion exercise with their most symptomatic leg to fatigue, followed by isometric handgrip until volitional fatigue at 40% of maximum on day 4 of supplementation, and a treadmill test to peak exertion 1-2 days later while continuing supplementation. Hemodynamics and exercise tolerance, and coronary blood flow velocity (CBV) responses were measured.

Results

Although peak walking time and claudication onset time during treadmill exercise did not differ significantly between BRplacebo and BRnitrate, the diastolic blood pressure response at the peak treadmill walking stage was significantly lower in the BRnitrate condition. Increases in CBV from baseline to peak plantar flexion exercise after BRplacebo and BRnitrate showed a trend for a greater increase in CBV at the peak workload of plantar flexion with BRnitrate (p = 0.06; Cohen's d = 0.56).

Conclusion

Overall, these preliminary findings suggest that inorganic nitrate supplementation in PAD patients is safe, well-tolerated, and may improve the coronary hyperemic and blood pressure responses when their calf muscles are most predisposed to ischemia.Clinical trial registration:https://clinicaltrials.gov/, identifier NCT02553733.

Effects of Acute Beetroot Juice Supplementation and Exercise on Cardiovascular Function in Healthy Men in Preliminary Study: A Randomized, Double-Blinded, Placebo-Controlled, and Crossover Trial

Nitrate-rich beetroot juice (NRBRJ) can potentially enhance exercise performance and improve cardiovascular function, leading to an increased use of NRBRJ over the years. However, the combined effects of NRBRJ supplementation and exercise on cardiovascular function remain unclear. Therefore, this study compared cardiovascular function responses to submaximal exercise with either placebo (PLA) or NRBRJ supplementation in healthy men. Twelve healthy men (aged 25.2 ± 2.3 years) completed the 30-min submaximal cycle ergometer exercise trials corresponding to 70% maximal heart rate (HRmax) with either PLA or NRBRJ supplementation in a random order. The mean exercise load, heart rate (HR), stroke volume (SV), cardiac output (CO), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and total peripheral resistance (TPR) were measured during exercise. The brachial-ankle pulse wave velocity (baPWV) and flow-mediated dilation (FMD) were measured before and after exercise. NRBRJ supplementation was more effective than PLA in increasing the mean exercise load and decreasing DBP and MAP during submaximal exercise. Furthermore, baPWV decreased in the NRBRJ trial and was considerably lower after exercise in the NRBRJ-supplemented group than in the PLA-supplemented group. FMD significantly increased in the PLA and NRBRJ trials; however, NRBRJ supplementation demonstrated a significantly higher FMD before and after exercise than PLA supplementation. In conclusion, acute NRBRJ supplementation and exercise were more effective than PLA supplementation and exercise in improving aerobic exercise capacity and cardiovascular function in healthy men.

Dietary nitrate supplementation and cognitive health: the nitric oxide-dependent neurovascular coupling hypothesis

Diet is currently recognized as a major modifiable agent of human health. In particular, dietary nitrate has been increasingly explored as a strategy to modulate different physiological mechanisms with demonstrated benefits in multiple organs, including gastrointestinal, cardiovascular, metabolic, and endocrine systems. An intriguing exception in this scenario has been the brain, for which the evidence of the nitrate benefits remains controversial. Upon consumption, nitrate can undergo sequential reduction reactions in vivo to produce nitric oxide (•NO), a ubiquitous paracrine messenger that supports multiple physiological events such as vasodilation and neuromodulation. In the brain, •NO plays a key role in neurovascular coupling, a fine process associated with the dynamic regulation of cerebral blood flow matching the metabolic needs of neurons and crucial for sustaining brain function. Neurovascular coupling dysregulation has been associated with neurodegeneration and cognitive dysfunction during different pathological conditions and aging. We discuss the potential biological action of nitrate on brain health, concerning the molecular mechanisms underpinning this association, particularly via modulation of •NO-dependent neurovascular coupling. The impact of nitrate supplementation on cognitive performance was scrutinized through preclinical and clinical data, suggesting that intervention length and the health condition of the participants are determinants of the outcome. Also, it stresses the need for multimodal quantitative studies relating cellular and mechanistic approaches to function coupled with behavior clinical outputs to understand whether a mechanistic relationship between dietary nitrate and cognitive health is operative in the brain. If proven, it supports the exciting hypothesis of cognitive enhancement via diet.

Acute effects of a chewable beetroot-based supplement on cognitive performance: a double-blind randomized placebo-controlled crossover clinical trial

BACKGROUND

Dietary nitrate (NO3-) has been shown to be useful as an ergogenic aid with potential applications in health and disease (e.g., blood pressure control). However, there is no consensus about the effects of dietary NO3- or beetroot (BR) juice supplementation on cognitive function.

OBJECTIVE

The aim of this study was to evaluate the effects of a single dose of a chewable BR-based supplement on cognitive performance.

METHODS

A double-blind randomized placebo-controlled two-period crossover clinical trial was carried out based on the extension of the CONSORT guidelines for randomized crossover trials. A total of 44 participants (24 F; 20 M; 32.7 [12.5] years; 66.3 [9.0] kg; 170 [9.2] cm; 22.8 [1.4] kg/m2) were randomly allocated to receive first either four BR-based chewable tablets (BR-CT) containing 3 g of a Beta vulgaris extract (RedNite®) or four tablets of a placebo (maltodextrin). A 4-day washout period was used before crossover. Ninety minutes after ingestion of the treatments, a neuropsychological testing battery was administered in each period. The trial was registered at clinicaltrials.gov NCT05509075.

RESULTS

Significant improvements with moderate effect size were found on memory consolidation at the short and long term only after BR-CT supplementation via the Rey Auditory Verbal Learning Test immediate (+ 20.69%) and delayed (+ 12.34%) recalls. Likewise, enhancement on both frontal lobe functions (+ 2.57%) and cognitive flexibility (+ 11.16%) were detected after BR-CT. There was no significant change (p < 0.05) on verbal memory of short-term digits, working memory and information processing speed. Mixed results were found on mood and anxiety through the Beck Depression Inventory-II (BDI-II) and the State-Trait Anxiety Inventory (STAI-Y1 and STAI-Y2); however, sequence and period effects were seen on STAI-Y2.

CONCLUSIONS

The acute administration of a chewable BR-based supplement improves certain aspects of cognitive function in healthy females and males, particularly memory capacity and frontal skills.

A review on nitrates' health benefits and disease prevention

Dietary nitrates (NO3-) are naturally occurring compounds in various vegetables, especially beetroot, which is mainly supplemented in the form of BRJ. Dietary nitrates (NO3-) play a crucial function in human physiology. On consumption, nitrates (NO3-) undergo a conversion process, producing nitric oxide (NO) via a complex metabolic pathway. Nitric oxide (NO) is associated with many physiological processes, entailing immune modulation, neurotransmission, and vasodilation, enabling blood vessel dilation and relaxation, which boosts blood flow and oxygen delivery to tissues, positively influencing cardiovascular health, exercise performance, and cognitive function. There are various analytical processes to determine the level of nitrate (NO3-) present in dietary sources. The impact of dietary nitrates (NO3-) can differ among individuals. Thus, the review revisits the dietary source of nitrates (NO3-), its metabolism, absorption, excretion, analytical techniques to assess nitrates (NO3-) content in various dietary sources, and discusses health effects.

The effect of eight weeks beetroot juice supplement on aerobic, anaerobic power, and field performance of soccer players

The purpose of the study investigated the effect of eight weeks of soccer training with beetroot juice supplement on aerobic power, anaerobic power, and field performance of soccer players. This is experimental research, by the control group in pre and post-test. The statistical population was male soccer players. Forty subjects were randomly divided into four groups including the exercise group (EX) the exercise group with beetroot juice supplement (EX&BRJS) the beetroot juice supplement group (BRJS), and the control group (C). Aerobic power, anaerobic threshold, and respiratory exchange ratio, measured by the gas analyser (Cosmed), anaerobic power (peak, mean power), and fatigue index, by Wingate cycle test (Monark, 839), and field performance by (Bangsbo, field test performance). The statistical methods include the Kolmogorov-Smirnov, Levin, covariance (ANCOVA), and pair comparison with Bonferroni test. The results showed eight weeks' of soccer training with beetroot juice supplement, significantly changed aerobic power, respiratory exchange ratio, anaerobic threshold, anaerobic power, field performance, and fatigue index (P ≤ 0.05). Additionally, in all variables, the paired comparison showed that the EX&BRJS group progressed more than all other condition groups. The soccer athletes may use beetroot juice supplements along with soccer exercises to improve aerobic and anaerobic power and field performance.

Does dietary nitrate boost the effects of caloric restriction on brain health? Potential physiological mechanisms and implications for future research

Dementia is a highly prevalent and costly disease characterised by deterioration of cognitive and physical capacity due to changes in brain function and structure. Given the absence of effective treatment options for dementia, dietary and other lifestyle approaches have been advocated as potential strategies to reduce the burden of this condition. Maintaining an optimal nutritional status is vital for the preservation of brain function and structure. Several studies have recognised the significant role of nutritional factors to protect and enhance metabolic, cerebrovascular, and neurocognitive functions. Caloric restriction (CR) positively impacts on brain function via a modulation of mitochondrial efficiency, endothelial function, neuro-inflammatory, antioxidant and autophagy responses. Dietary nitrate, which serves as a substrate for the ubiquitous gasotransmitter nitric oxide (NO), has been identified as a promising nutritional intervention that could have an important role in improving vascular and metabolic brain regulation by affecting oxidative metabolism, ROS production, and endothelial and neuronal integrity. Only one study has recently tested the combined effects of both interventions and showed preliminary, positive outcomes cognitive function. This paper explores the potential synergistic effects of a nutritional strategy based on the co-administration of CR and a high-nitrate diet as a potential and more effective (than either intervention alone) strategy to protect brain health and reduce dementia risk.

Effects of dietary nitrate supplementation on peak power output: Influence of supplementation strategy and population

Increasing evidence indicates that dietary nitrate supplementation has the potential to increase muscular power output during skeletal muscle contractions. However, there is still a paucity of data characterizing the impact of different nitrate dosing regimens on nitric oxide bioavailability and its potential ergogenic effects across various population groups. This review discusses the potential influence of different dietary nitrate supplementation strategies on nitric oxide bioavailability and muscular peak power output in healthy adults, athletes, older adults and some clinical populations. Effect sizes were calculated for peak power output and absolute and/or relative nitrate doses were considered where applicable. There was no relationship between the effect sizes of peak power output change following nitrate supplementation and when nitrate dosage when considered in absolute or relative terms. Areas for further research are also recommended including a focus on nitrate dosing regimens that optimize nitric oxide bioavailability for enhancing peak power at times of increased muscular work in a variety of healthy and disease populations.

Reduction in blood pressure following acute dietary nitrate ingestion is correlated with increased red blood cell S-nitrosothiol concentrations

Dietary nitrate (NO3-) supplementation can enhance nitric oxide (NO) bioavailability and lower blood pressure (BP) in humans. The nitrite concentration ([NO2-]) in the plasma is the most commonly used biomarker of increased NO availability. However, it is unknown to what extent changes in other NO congeners, such as S-nitrosothiols (RSNOs), and in other blood components, such as red blood cells (RBC), also contribute to the BP lowering effects of dietary NO3-. We investigated the correlations between changes in NO biomarkers in different blood compartments and changes in BP variables following acute NO3- ingestion. Resting BP was measured and blood samples were collected at baseline, and at 1, 2, 3, 4 and 24 h following acute beetroot juice (∼12.8 mmol NO3-, ∼11 mg NO3-/kg) ingestion in 20 healthy volunteers. Spearman rank correlation coefficients were determined between the peak individual increases in NO biomarkers (NO3-, NO2-, RSNOs) in plasma, RBC and whole blood, and corresponding decreases in resting BP variables. No significant correlation was observed between increased plasma [NO2-] and reduced BP, but increased RBC [NO2-] was correlated with decreased systolic BP (rs = -0.50, P = 0.03). Notably, increased RBC [RSNOs] was significantly correlated with decreases in systolic (rs = -0.68, P = 0.001), diastolic (rs = -0.59, P = 0.008) and mean arterial pressure (rs = -0.64, P = 0.003). Fisher's z transformation indicated no difference in the strength of the correlations between increases in RBC [NO2-] or [RSNOs] and decreased systolic blood pressure. In conclusion, increased RBC [RSNOs] may be an important mediator of the reduction in resting BP observed following dietary NO3- supplementation.

Dietary nitrate intake in relation to the risk of dementia and imaging markers of vascular brain health: a population-based study

BACKGROUND

Nitric oxide is a free radical that can be produced from dietary nitrate and positively affects cardiovascular health. With cardiovascular health playing an important role in the etiology of dementia, we hypothesized a link between dietary nitrate intake and the risk of dementia.

OBJECTIVES

This study aimed to find the association of total, vegetable, and nonvegetable dietary nitrate intake with the risk of dementia and imaging markers of vascular brain health, such as total brain volume, global cerebral perfusion, white matter hyperintensity volume, microbleeds, and lacunar infarcts.

METHODS

Between 1990 and 2009, dietary intake was assessed using food-frequency questionnaires in 9543 dementia-free participants (mean age, 64 y; 58% female) from the prospective population-based Rotterdam Study. Participants were followed up for incidence dementia until January 2020. We used Cox models to determine the association between dietary nitrate intake and incident dementia. Using linear mixed models and logistic regression models, we assessed the association of dietary nitrate intake with changes in imaging markers across 3 consecutive examination rounds (mean interval between images 4.6 y).

RESULTS

Participants median dietary nitrate consumption was 85 mg/d (interquartile range, 55 mg/d), derived on average for 81% from vegetable sources. During a mean follow-up of 14.5 y, 1472 participants developed dementia. A higher intake of total and vegetable dietary nitrate was associated with a lower risk of dementia per 50-mg/d increase [hazard ratio (HR): 0.92; 95% confidence interval (CI): 0.87, 0.98; and HR: 0.92; 95% CI: 0.86, 0.97, respectively] but not with changes in neuroimaging markers. No association between nonvegetable dietary nitrate intake and the risk of dementia (HR: 1.15; 95% CI: 0.64, 2.07) or changes in neuroimaging markers were observed.

CONCLUSIONS

A higher dietary nitrate intake from vegetable sources was associated with a lower risk of dementia. We found no evidence that this association was driven by vascular brain health.

"Diet for the prevention and management of sarcopenia"

Sarcopenia is a geriatric condition characterized by a progressive loss of skeletal muscle mass and strength, with an increased risk of adverse health outcomes (e.g., falls, disability, institutionalization, reduced quality of life, mortality). Pharmacological remedies are currently unavailable for preventing the development of sarcopenia, halting its progression, or impeding its negative health outcomes. The most effective strategies to contrast sarcopenia rely on the adoption of healthier lifestyle behaviors, including adherence to high-quality diets and regular physical activity. In this review, the role of nutrition in the prevention and management of sarcopenia is summarized. Special attention is given to current "blockbuster" dietary regimes and agents used to counteract age-related muscle wasting, together with their putative mechanisms of action. Issues related to the design and implementation of effective nutritional strategies are discussed, with a focus on unanswered questions on the most appropriate timing of nutritional interventions to preserve muscle health and function into old age. A brief description is also provided on new technologies that can facilitate the development and implementation of personalized nutrition plans to contrast sarcopenia.

Habitual dietary nitrate intake and cognition in the Australian Imaging, Biomarkers and Lifestyle Study of ageing: A prospective cohort study

BACKGROUND & AIMS

Dietary nitrate improves cardiovascular health via a nitric oxide (NO) pathway. NO is key to both cardiovascular and brain health. There is also a strong association between vascular risk factors and brain health. Dietary nitrate intake could therefore be associated with better cognitive function and reduced risk of cognitive decline. This is yet to be investigated. The aim of this study was to investigate the association between habitual intake of dietary nitrate from sources where nitrate is naturally present, and cognitive function, and cognitive decline, in the presence or absence of the apolipoprotein E (APOE) ε4 allele.

METHODS

The study included 1254 older adult participants of the Australian Imaging, Biomarkers and Lifestyle Study of Ageing who were cognitively normal at baseline. Plant-derived, vegetable-derived, animal derived nitrate (not including meat where nitrate is an allowed additive), and total nitrate intakes were calculated from baseline food frequency questionnaires using comprehensive nitrate databases. Cognition was assessed at baseline and every 18 months over a follow-up period of 126 months using a comprehensive neuropsychological test battery. Multivariable-adjusted linear mixed effect models were used to examine the association between baseline nitrate intake and cognition over the 126 months (median [IQR] follow-up time of 36 [18-72] months), stratified by APOE ε4 carrier status.

RESULTS

In non APOE ε4 carriers, for every 60 mg/day higher intake of plant-derived nitrate at baseline there was an associated higher language score [β (95% CI): 0.10 (0.01, 0.19)] over 126 months, after multivariable adjustments. In APOE ε4 carriers, there was an associated better episodic recall memory [0.24 (0.08, 0.41)] and recognition memory [0.15 (0.01, 0.30)] scores. Similar associations were seen for the intakes of vegetable-derived and total nitrate. Additionally, in APOE ε4 carriers, for every 6 mg/day higher intake of animal-derived nitrate (excluding meat with nitrate as an allowed additive) at baseline there was an associated higher executive function score [β (95% CI): 1.41 (0.42, 2.39)]. We did not find any evidence of an association between dietary nitrate intake and rate of cognitive decline.

CONCLUSION

Our results suggest that habitual intake of dietary nitrate from sources where nitrate is naturally present impacts cognitive performance in an APOE genotype contingent manner. Further work is needed to validate our findings and understand potential mechanisms underlying the observed effects.

Effects of dietary nitrate supplementation on muscular power output: Influence of supplementation strategy and population

Increasing evidence indicates that dietary nitrate supplementation has the potential to increase muscular power output during skeletal muscle contractions. However, there is still a paucity of data characterizing the impact of different nitrate dosing regimens on nitric oxide bioavailability its potential ergogenic effects across various population groups. This narrative review discusses the potential influence of different dietary nitrate supplementation strategies on nitric oxide bioavailability and muscular power output in healthy adults, athletes, older adults and some clinical populations. Areas for further research are also recommended including a focus individualized nitrate dosing regimens to optimize nitric oxide bioavailability and to promote muscular power enhancements in different populations.

The influence of acute dietary nitrate supplementation on skeletal muscle fatigue and recovery in older women

Older individuals fatigue more rapidly during, and recover more slowly from, dynamic exercise. Women are particularly vulnerable to these deleterious effects of aging, which increases their risk of falling. We have shown that dietary nitrate (NO3 - ), a source of nitric oxide (NO) via the NO3 -  → nitrite (NO2 - ) → NO pathway, enhances muscle speed and power in older individuals in the non-fatigued state; however, it is unclear if it reduces fatigability and/or improves recoverability in this population. Using a double-blind, placebo-controlled, crossover design, we studied 18 older (age 70 ± 4 years) women who were administered an acute dose of beetroot juice (BRJ) containing either 15.6 ± 3.6 or <0.05 mmol of NO3 - . Blood samples were drawn throughout each ~3 h visit for plasma NO3 - and NO2 - analysis. Peak torque was measured during, and periodically for 10 min after, 50 maximal knee extensions performed at 3.14 rad/s on an isokinetic dynamometer. Ingestion of NO3 - -containing BRJ increased plasma NO3 - and NO2 - concentrations by 21 ± 8 and 4 ± 4 fold, respectively. However, there were no differences in muscle fatigue or recovery. Dietary NO3 - increases plasma NO3 - and NO2 - concentrations but does not reduce fatigability during or enhance recoverability after high intensity exercise in older women.

Dietary nitrate biochemistry and physiology. An update on clinical benefits and mechanisms of action

It is now more than 35 years since endothelium derived relaxing factor was identified as nitric oxide (NO). The last few decades have seen an explosion around nitric oxide biochemistry, physiology and clinical translation. The science reveals that all chronic disease is associated with decreased blood flow to the affected organ which results in increased inflammation, oxidative stress and immune dysfunction. This is true for cardiovascular disease, neurological disease, kidney, lung, liver disorders and every other major disorder. Since nitric oxide controls and regulates blood flow, oxygen and nutrient delivery to every cell, tissue and organ in the body and also mitigates inflammation, oxidative stress and immune dysfunction, a focus on restoring nitric oxide production is an obvious therapeutic strategy for a number of poorly managed chronic diseases. Since dietary nitrate is a major contributor to endogenous nitric oxide production, it should be considered as a means of therapy and restoration of nitric oxide. This review will update on the current state of the science and effects of inorganic nitrate administered through the diet on several chronic conditions and reveal how much is needed. It is clear now that antiseptic mouthwash and use of antacids disrupt nitrate metabolism to nitric oxide leading to clinical symptoms of nitric oxide deficiency. Based on the science, nitrate should be considered an indispensable nutrient that should be accounted for in dietary guidelines.

Ageing modifies acute resting blood pressure responses to incremental consumption of dietary nitrate: a randomised, cross-over clinical trial

Beetroot (BR) is a rich source of nitrate (NO₃-) that has been shown to reduce blood pressure (BP). Yet, no studies have examined the vascular benefits of BR in whole-food form and whether the effects are modified by age. This study was a four-arm, randomised, open-label, cross-over design in twenty-four healthy adults (young n 12, age 27 ± 4 years, old n 12, age 64 ± 5 years). Participants consumed whole-cooked BR at portions of (NO₃- content in brackets) 100 g (272 mg), 200 g (544 mg) and 300 g (816 mg) and a 200-ml solution containing 1000 mg of potassium nitrate (KNO₃) on four separate occasions over a 4-week period (≥7-d washout period). BP, plasma NO₃- and nitrite (NO₂-) concentrations, and post-occlusion reactive hyperaemia via laser Doppler, were measured pre- and up to 5-h post-intervention. Data were analysed by repeated-measures ANOVA. Plasma NO₂- concentrations were higher in the young v. old at baseline and post-intervention (P < 0·05). All NO₃- interventions decreased systolic and diastolic BP in young participants (P < 0·05), whereas only KNO₃ (at 240-300 min post-intake) significantly decreased systolic (-4·8 mmHg, -3·5 %, P = 0·024) and diastolic (-5·4 mmHg, -6·5 %, P = 0·007) BP in older participants. In conclusion, incremental doses of dietary NO₃- reduced systolic and diastolic BP in healthy young adults whereas in the older group a significant decrease was only observed with the highest dose. The lower plasma NO₂- concentrations in older participants suggest that there may be mechanistic differences in the production of NO from dietary NO₃- in young and older populations.

Dietary nitrate supplementation enhances heavy load carriage performance in military cadets

PURPOSE

To determine the effects of dietary nitrate (NO₃^-) supplementation on physiological responses, cognitive function, and performance during heavy load carriage in military cadets.

METHODS

Ten healthy males (81.0 ± 6.5 kg; 180.0 ± 4.5 cm; 56.2 ± 3.7 ml·kg·min^-1 VO_2max) consumed 140 mL·d^-1 of beetroot juice (BRJ; 12.8 mmol NO₃^-) or placebo (PL) for six d preceding an exercise trial, which consisted of 45 min of load carriage (55% body mass) at 4.83 km·h^-1 and 1.5% grade, followed by a 1.6-km time-trial (TT) at 4% grade. Gas exchange, heart rate, and perceptual responses were assessed during constant-load exercise and the TT. Cognitive function was assessed immediately prior to, during, and post-exercise via the psychomotor vigilance test (PVT).

RESULTS

Post-TT HR (188 ± 7.1 vs. 185 ± 7.4; d = 0.40; p = 0.03), mean tidal volume (2.15 ± 0.27 vs. 2.04 ± 0.23; p = 0.02; d = 0.47), and performance (770.9 ± 78.2 s vs. 809.8 ± 61.4 s; p = 0.03; d = 0.63) were increased during the TT with BRJ versus PL. There were no effects of BRJ on constant-load gas exchange or perceptual responses, and cognitive function was unchanged at all time points.

CONCLUSION

BRJ supplementation improves heavy load carriage performance in military cadets possibly as a result of attenuated respiratory muscle fatigue, rather than enhanced exercise economy.

Inorganic nitrate supplementation may improve diastolic function and the O2 cost of exercise in cancer survivors: a pilot study

In non-cancer populations, inorganic dietary nitrate (NO₃^-) supplementation is associated with enhanced cardiorespiratory function but remains untested in patients with a history of cancer. Therefore, this pilot study sought to determine if oral NO₃^- supplementation, as a supportive care strategy, increases left ventricular (LV) function and exercise performance in survivors of cancer treated with anticancer therapy while simultaneously evaluating the feasibility of the methods and procedures required for future large-scale randomized trials. Two cohorts of patients with a history of cancer treated with anticancer chemotherapy were recruited. Patients in cohort 1 (n = 7) completed a randomized, double-blind, crossover study with 7 days of NO₃^- or placebo (PL) supplementation, with echocardiography. Similarly, patients in cohort 2 (n = 6) received a single, acute dose of NO₃^- supplementation or PL. Pulmonary oxygen uptake (VO₂), arterial blood pressure, and stroke volume were assessed during exercise. In cohort 1, NO₃^- improved LV strain rate in early filling (mean difference (MD) [95% CI]: - 0.3 1/s [- 0.6 to 0.06]; P = 0.04) and early mitral septal wall annular velocity (MD [95% CI]: 0.1 m/s [- 0.01 to - 0.001]; P = 0.02) compared to placebo. In cohort 2, NO₃^- decreased the O₂ cost of low-intensity steady-state exercise (MD [95% CI]: - 0.5 ml/kg/min [- 0.9 to - 0.09]; P = 0.01). Resting and steady-state arterial blood pressure and stroke volume were not different between conditions. No differences between conditions for peak VO₂ (MD [95% CI]: - 0.7 ml/kg/min [- 3.0 to 1.6]; P = 0.23) were observed. The findings from this pilot study warrant further investigation in larger clinical trials targeting the use of long-term inorganic dietary NO₃^- supplementation as a possible integrative supportive care strategy in patients following anticancer therapy.

Efficacy and Variability in Plasma Nitrite Levels during Long-Term Supplementation with Nitrate Containing Beetroot Juice

Long-term consumption of beetroot juice on efficacy of converting dietary nitrate to plasma nitrate and nitrite was investigated. Adults were randomized to consume either beetroot juice with 380 mg of nitrate (BR) or a beetroot juice placebo (PL) for 12-weeks. Plasma nitrate and nitrite were measured before and 90-minutes after consuming their intervention beverage. Percent change in nitrite across the 90 min was greater in BR (273.2 ± 39.9%) vs. PL (4.9 ± 36.9%). Long-term consumption of nitrate containing beetroot juice increased fasting nitrate and nitrite plasma levels compared to baseline.

Dietary Inorganic Nitrate as an Ergogenic Aid: An Expert Consensus Derived via the Modified Delphi Technique

INTRODUCTION

Dietary inorganic nitrate is a popular nutritional supplement, which increases nitric oxide bioavailability and may improve exercise performance. Despite over a decade of research into the effects of dietary nitrate supplementation during exercise there is currently no expert consensus on how, when and for whom this compound could be recommended as an ergogenic aid. Moreover, there is no consensus on the safe administration of dietary nitrate as an ergogenic aid. This study aimed to address these research gaps.

METHODS

The modified Delphi technique was used to establish the views of 12 expert panel members on the use of dietary nitrate as an ergogenic aid. Over three iterative rounds (two via questionnaire and one via videoconferencing), the expert panel members voted on 222 statements relating to dietary nitrate as an ergogenic aid. Consensus was reached when > 80% of the panel provided the same answer (i.e. yes or no). Statements for which > 80% of the panel cast a vote of insufficient evidence were categorised as such and removed from further voting. These statements were subsequently used to identify directions for future research.

RESULTS

The 12 panel members contributed to voting in all three rounds. A total of 39 statements (17.6%) reached consensus across the three rounds (20 yes, 19 no). In round one, 21 statements reached consensus (11 yes, 10 no). In round two, seven further statements reached consensus (4 yes, 3 no). In round three, an additional 11 statements reached consensus (5 yes, 6 no). The panel agreed that there was insufficient evidence for 134 (60.4%) of the statements, and were unable to agree on the outcome of the remaining statements.

CONCLUSIONS

This study provides information on the current expert consensus on dietary nitrate, which may be of value to athletes, coaches, practitioners and researchers. The effects of dietary nitrate appear to be diminished in individuals with a higher aerobic fitness (peak oxygen consumption [V̇O2peak] > 60 ml/kg/min), and therefore, aerobic fitness should be taken into account when considering use of dietary nitrate as an ergogenic aid. It is recommended that athletes looking to benefit from dietary nitrate supplementation should consume 8-16 mmol nitrate acutely or 4-16 mmol/day nitrate chronically (with the final dose ingested 2-4 h pre-exercise) to maximise ergogenic effects, taking into consideration that, from a safety perspective, athletes may be best advised to increase their intake of nitrate via vegetables and vegetable juices. Acute nitrate supplementation up to ~ 16 mmol is believed to be safe, although the safety of chronic nitrate supplementation requires further investigation. The expert panel agreed that there was insufficient evidence for most of the appraised statements, highlighting the need for future research in this area.

A comprehensive review of beetroot (Beta vulgaris L.) bioactive components in the food and pharmaceutical industries

Beetroot is rich in various bioactive phytochemicals, which are beneficial for human health and exert protective effects against several disease conditions like cancer, atherosclerosis, etc. Beetroot has various therapeutic applications, including antioxidant, antibacterial, antiviral, and analgesic functions. Besides the pharmacological effects, food industries are trying to preserve beetroots or their phytochemicals using various food preservation methods, including drying and freezing, to preserve their antioxidant capacity. Beetroot is a functional food due to valuable active components such as minerals, amino acids, phenolic acid, flavonoid, betaxanthin, and betacyanin. Due to its stability, nontoxic and non-carcinogenic and nonpoisonous capabilities, beetroot has been used as an additive or preservative in food processing. Beetroot and its bioactive compounds are well reported to possess antioxidant, anti-inflammatory, antiapoptotic, antimicrobial, antiviral, etc. In this review, we provided updated details on (i) food processing, preservation and colorant methods using beetroot and its phytochemicals, (ii) synthesis and development of several nanoparticles using beetroot and its bioactive compounds against various diseases, (iii) the role of beetroot and its phytochemicals under disease conditions with molecular mechanisms. We have also discussed the role of other phytochemicals in beetroot and their health benefits. Recent technologies in food processing are also updated. We also addressed on molecular docking-assisted biological activity and screening for bioactive chemicals. Additionally, the role of betalain from different sources and its therapeutic effects have been listed. To the best of our knowledge, little or no work has been carried out on the impact of beetroot and its nanoformulation strategies for phytocompounds on antimicrobial, antiviral effects, etc. Moreover, epigenetic alterations caused by phytocompounds of beetroot under several diseases were not reported much. Thus, extensive research must be carried out to understand the molecular effects of beetroot in the near future.

Nutritional interventions for improving the endurance performance in athletes

Endurance refers to the ability of skeletal muscles to perform continuously withstanding the hardships of exercise. Endurance exercises have three phases: pre-, during-, and post-workout phase. The nutritional requirements that drive these phases vary on intensity, type of workout, individual's body composition, training, weather conditions, etc. Generally, the pre-workout phase requires glycogen synthesis and spare glycogen breakdown. While workout phase, requires rapid absorption of exogenous glucose, insulin release to transport glucose into muscle cells, replenish the loss of electrolytes, promote fluid retention, etc. However, post-workout phase requires quick amino acid absorption, muscle protein synthesis, repair of damaged muscle fibres and tendon, ameliorate inflammation, oxidative stress, etc. Therefore, nutritional sources that can help these metabolic requirements is recommended. In this review, various dietary interventions including timing and amount of nutrient consumption that can promote the above metabolic requirements that in turn support in improving the endurance potential in athletes are discussed.HIGHLIGHTSReview article describes nutritional requirements of endurance exercises.It also describes nutritional interventions to enhance the endurance potential in athletes.

Dietary Nitrate Supplementation and Small Muscle Mass Exercise Hemodynamics in Patients with Essential Hypertension

Exaggerated blood pressure and diminished limb hemodynamics during exercise in patients with hypertension often are not resolved by antihypertensive medications. We hypothesized that, independent of antihypertensive medication status, dietary nitrate supplementation would increase limb blood flow, decrease mean arterial pressure (MAP), and increase limb vascular conductance during exercise in patients with hypertension. Patients with hypertension either abstained from (n=14, Off-Meds) or continued (n=12, On-Meds) antihypertensive medications. Within each group, patients consumed (cross-over design) nitrate-rich or nitrate-depleted (placebo) beetroot juice for 3-days before performing handgrip (HG) and knee-extensor exercise (KE). Blood flow and MAP were measured using Doppler ultrasound and an automated monitor, respectively. Dietary nitrate increased plasma-[nitrite] Off-Meds and On-Meds. There were no significant effects of dietary nitrate on blood flow, MAP, or vascular conductance during HG in Off-Meds or On-Meds. For KE, dietary nitrate decreased MAP (mean±SD across all three exercise intensities, 118±14 vs. 122±14 mmHg, p=0.024) and increased vascular conductance (26.2±6.1 vs. 24.7±7.0 ml/min/mmHg, p=0.024), but did not affect blood flow for Off-Meds, with no effects On-Meds. Dietary nitrate-induced changes in blood flow (r=-0.67, p<0.001), MAP (r=-0.43, p=0.009), and vascular conductance (r=-0.64, p<0.001) during KE, but only vascular conductance (r=-0.35, p=0.039) during HG, were significantly related to the magnitude of placebo values, with no differentiation between groups. Thus, the effects of dietary nitrate on limb hemodynamics and MAP during exercise in patients with hypertension are dependent on the values at baseline, independent of antihypertensive medication status, and dependent on whether exercise was performed by the forearm or quadriceps.

Effect of Vitamin C and Protein Supplementation on Plasma Nitrate and Nitrite Response following Consumption of Beetroot Juice

Beetroot juice is a food high in nitrate and is associated with cardiometabolic health benefits and enhanced exercise performance through the production of nitric oxide in the nitrate−nitrite−nitric oxide pathway. Since various food components influence this pathway, the aim of this trial was to study the effect of beetroot juice alone and in conjunction with vitamin C or protein on the acute response to plasma nitrate and nitrite levels in healthy middle- to older-aged adults. In this cross-over trial, each participant received, in a randomized order, a single dose of Beet It Sport® alone; Beet It Sport®, plus a 200 mg vitamin C supplement; and Beet It Sport® plus 15 g of whey protein. Plasma levels of nitrate and nitrite were determined prior to and at 1 and 3 h after intervention. Log plasma nitrate and nitrite was calculated to obtain data that were normally distributed, and these data were analyzed using two-way within-factors ANOVA, with time and treatment as the independent factors. There were no statistically significant differences for log plasma nitrate (p = 0.308) or log plasma nitrite (p = 0.391) values across treatments. Log plasma nitrate increased significantly from pre-consumption levels after 1 h (p < 0.001) and 3 h (p < 0.001), but plasma nitrate was lower at 3 h than 1 h (p < 0.001). Log plasma nitrite increased from pre to 1 h (p < 0.001) and 3 h (p < 0.001) with log values at 3 h higher than at 1 h (p = 0.003). In this cohort, we observed no differences in log plasma nitrate and nitrite at 1 h and 3 h after co-ingesting beetroot juice with vitamin C or a whey protein supplement compared to beetroot juice alone. Further research needs to be undertaken to expand the blood-sampling time-frame and to examine factors that may influence the kinetics of the plasma nitrate to nitrite efficacy, such as differences in fluid volume and osmolarity between treatments employed.

Development of biscuits supplemented with papaya seed and peel: effects on physicochemical properties, bioactive compounds, in vitro absorption capacities and starch digestibility

In this study, wheat biscuits were prepared by supplementing with papaya seed (PS) and papaya peel (PP) in range of 2 to 10%. As compared to control (un-supplemented) samples, PS and PP-supplemented biscuits were analyzed for their physicochemical properties, bioactive compounds, antioxidant activities, in vitro absorption capacities, starch digestibility and sensory attributes. As compared to PS, PP had lower energy value, higher bioactive compounds and antioxidant activity along with better in vitro adsorption capacities. Overall, PS and PP addition from 2 to 10% significantly improved nutritional components, polyphenol compounds, antioxidant activities, and caused marked rises in NO₂ ^- ion, cholesterol and bile acid absorption capacities of supplemented biscuits. Moreover, PS and PP-addition showed significant concentration-dependent decreases in glucose release response during various in vitro starch digestion intervals. Based on sensory characteristics, biscuits supplemented up to 4% PS and PP showed excellent overall acceptability, however, in comparison with PS, 4% PP-supplemented biscuits exhibited the better sensory properties. Therefore, PP-supplemented biscuits up to 4% could be utilized as a convenience food. Moreover, PS and PP-supplementation of wheat biscuits led to improvement of functional properties as a valuable source of bioactive compounds and high radical-scavenging activities.

Incremental Doses of Nitrate-Rich Beetroot Juice Do Not Modify Cognitive Function and Cerebral Blood Flow in Overweight and Obese Older Adults: A 13-Week Pilot Randomised Clinical Trial

Nitrate-rich food increases nitric oxide (NO) production and may have beneficial effects on vascular, metabolic, and brain function. This pilot study tested the effects of prolonged consumption of a range of doses of dietary nitrate (NO₃^-), provided as beetroot juice, on cognitive function and cerebral blood flow (CBF) in overweight and obese older participants. The study had a 13-week single-blind, randomised, parallel design, and 62 overweight and obese older participants (aged 60 to 75 years) received the following interventions: (1) high NO₃^- (2 × 70 mL beetroot juice/day) (2) medium NO₃^- (70 mL beetroot juice/day), (3) low NO₃^- (70 mL beetroot juice on alternate days), or (4) placebo (70 mL of NO₃^--depleted beetroot juice on alternate days). Cognitive functions were assessed using the Computerised Mental Performance Assessment System (COMPASS) assessment battery. CBF, monitored by concentration changes in oxygenated and deoxygenated haemoglobin, was assessed in the frontal cortex using near-infrared spectroscopy. The findings of this pilot study showed that cognitive function and CBF were not affected by supplementation with NO₃^--rich beetroot juice for 13 weeks, irrespective of the NO₃^- dose administered. These findings require confirmation in larger studies using more sophisticated imaging methods (i.e., MRI) to determine whether prolonged dietary NO₃^- supplementation influences brain function in older overweight people.

Role of nitric oxide in convective and diffusive skeletal microvascular oxygen kinetics

Progress in understanding physiological mechanisms often consists of discrete discoveries made across different models and species. Accordingly, understanding the mechanistic bases for how altering nitric oxide (NO) bioavailability impacts exercise tolerance (or not) depends on integrating information from cellular energetics and contractile regulation through microvascular/vascular control of O₂ transport and pulmonary gas exchange. This review adopts state-of-the-art concepts including the intramyocyte power grid, the Wagner conflation of perfusive and diffusive O₂ conductances, and the Critical Power/Critical Speed model of exercise tolerance to address how altered NO bioavailability may, or may not, affect physical performance. This question is germane from the elite athlete to the recreational exerciser and particularly the burgeoning heart failure (and other clinical) populations for whom elevating O₂ transport and/or exercise capacity translates directly to improved life quality and reduced morbidity and mortality. The dearth of studies in females is also highlighted, and areas of uncertainty and questions for future research are identified.

Probabilistic risk and benefit assessment of nitrates and nitrites by integrating total diet study-based exogenous dietary exposure with endogenous nitrite formation using toxicokinetic modeling

The impacts of dietary nitrates and nitrites on human health have been a controversial topic for many years. However, the risk and benefit assessment of nitrates and nitrites is complicated by the large variation in nitrate and nitrite intake among people and the endogenous nitrite formation in the body. This study conducted a probabilistic risk-benefit assessment of dietary nitrates and nitrites based on internal dose by integrating exogenous and endogenous exposures with human trial data on cardiovascular benefits. A total diet study was carried out to quantify the age-specific dietary intakes of nitrates and nitrites. A previously well-validated human toxicokinetic model was used to predict internal doses for different age groups. In addition, the integrated approach was applied to different populations from different countries/regions based on reported exposure estimates to conduct a comprehensive risk-benefit assessment of dietary nitrates and nitrites. The results demonstrated that vegetable consumption was the main contributor to the internal nitrate and nitrite levels in all age groups. Exposure to nitrates and nitrites exceeding acceptable daily intakes in a variety of foods showed cardiovascular benefits. The probabilistic risk assessment showed that the exposure to nitrates and nitrites did not pose an appreciable health and safety risk. Therefore, the present results suggest that dietary nitrates and nitrites have clear cardiovascular benefits that may outweigh potential risks. Our analysis contributes significantly to addressing the controversy regarding risks and benefits from dietary nitrates and nitrites, and our approach could be applied to other dietary constituents with the potential for both risks and benefits.

The Nitrate-Nitrite-Nitric Oxide Pathway on Healthy Ageing: A Review of Pre-clinical and Clinical Data on the Impact of Dietary Nitrate in the Elderly

We are living longer. Are we living healthier? As we age, cellular and molecular damage reshape our physiological responses towards environmental and endogenous stimuli. The free radical theory of ageing has been proposed long before ageing has been considered a “scientific discipline” and, since then, has been discussed and upgraded as a major contributor to aberrant ageing. Assuming that ageing results merely from the accumulation of oxidative modifications of biomolecules is not only a simplistic and reductive view of such a complex and dynamic process, but also free radicals and related oxidants are now considered pivotal signalling molecules. The fine modulation of critical signalling pathways by redox compounds demands a novel approach to tackle the role of free radicals in ageing. Nitric oxide (^⋅NO) is a paradigmatic example given its biological functions in cardiovascular, neurologic and immune systems. In addition to the canonical ^⋅NO synthesis by a family of enzymes, nitrate from green leafy vegetables, is reduced to nitrite in the oral cavity which is further reduced to ^⋅NO in the stomach. Boosting this nitrate-nitrite-NO pathway has been shown to improve gastrointestinal, cardiovascular, metabolic and cognitive performance both in humans and in animal models of disease. In the elderly, nitrate-derived ^⋅NO has been shown improve several physiological functions that typically decline during ageing. In this paper, the role of nitrate and derived nitrogen oxides will be discussed while reviewing pre-clinical and clinical data on the cardiovascular, neuronal, musculoskeletal and metabolic effects of nitrate during healthy ageing.

Pink pressure: beetroot (Beta vulgaris rubra) as a possible novel medical therapy for chronic kidney disease

Chronic kidney disease (CKD) manifests with systemic inflammation, oxidative stress, and gut dysbiosis, resulting in metabolic disorders and elevated rates of cardiovascular disease-associated death. These all correlate with a high economic cost to healthcare systems. Growing evidence indicates that diet is an indispensable ally in the prevention and management of CKD and its complications. In this context, the root vegetable beetroot (Beta vulgaris rubra) deserves special attention because it is a source of several bioactive compounds, such as nitrate, betaine, and betalain, and has shown beneficial effects in CKD, including reduction of blood pressure, anti-inflammatory effects, and antioxidant actions by scavenging radical oxidative species, as observed in preclinical studies. Beetroot consumption as a possible therapeutic strategy to improve the clinical treatment of patients with CKD and future directions for clinical studies are addressed in this narrative review.

Increasing Nitrate-Rich Vegetable Intake Lowers Ambulatory Blood Pressure in (pre)Hypertensive Middle-Aged and Older Adults: A 12-Wk Randomized Controlled Trial

BACKGROUND

Emerging evidence suggests that increasing dietary nitrate intake may be an effective approach to improve cardiovascular health. However, the effects of a prolonged elevation of nitrate intake through an increase in vegetable consumption are understudied.

OBJECTIVE

Our primary aim was to determine the impact of 12 wk of increased daily consumption of nitrate-rich vegetables or nitrate supplementation on blood pressure (BP) in (pre)hypertensive middle-aged and older adults.

METHODS

In a 12-wk randomized, controlled study (Nijmegen, The Netherlands), 77 (pre)hypertensive participants (BP: 144 ± 13/87 ± 7 mmHg, age: 65 ± 10 y) either received an intervention with personalized monitoring and feedback aiming to consume ∼250-300 g nitrate-rich vegetables/d (∼350-400 mg nitrate/d; n = 25), beetroot juice supplementation (400 mg nitrate/d; n = 26), or no intervention (control; n = 26). Before and after intervention, 24-h ambulatory BP was measured. Data were analyzed using repeated measures ANOVA (time × treatment), followed by within-group (paired t-test) and between-group analyses (1-factor ANOVA) where appropriate.

RESULTS

The 24-h systolic BP (SBP) (primary outcome) changed significantly (P-interaction time × treatment = 0.017) with an increase in the control group (131 ± 8 compared with 135 ± 10 mmHg; P = 0.036); a strong tendency for a decline in the nitrate-rich vegetable group (129 ± 10 compared with 126 ± 9 mmHg; P = 0.051) which was different from control (P = 0.020); but no change in the beetroot juice group (133 ± 11 compared with 132 ± 12 mmHg; P = 0.56). A significant time × treatment interaction was also found for daytime SBP (secondary outcome, P = 0.011), with a significant decline in the nitrate-rich vegetable group (134 ± 10 compared with 129 ± 9 mmHg; P = 0.006) which was different from control (P = 0.010); but no changes in the beetroot juice (138 ± 12 compared with 137 ± 14 mmHg; P = 0.41) and control group (136 ± 10 compared with 137 ± 11 mmHg; P = 0.08). Diastolic BP (secondary outcome) did not change in any of the groups.

CONCLUSIONS

A prolonged dietary intervention focusing on high-nitrate vegetable intake is an effective strategy to lower SBP in (pre)hypertensive middle-aged and older adults. This trial was registered at www.trialregister.nl as NL7814.

Effects of Dietary Food Components on Cognitive Functions in Older Adults

Population aging has recently been an important issue as the number of elderly people is growing worldwide every year, and the extension of social security costs is financially costly. The increase in the number of elderly people with cognitive decline is a serious problem related to the aging of populations. Therefore, it is necessary to consider not only physical care but also cognitive patterns in the future care of older adults. Since food contains a variety of bioactive substances, dietary patterns may help improve age-related cognitive decline. However, the relationship between cognitive function and individual food components remains ambiguous as no clear efficacy or mechanism has been confirmed. Against this background, this review summarizes previous reports on the biological process of cognitive decline in the elderly and the relationship between individual compounds in foods and cognitive function, as well as the role of individual components of food in cognitive function, in the following order: lipids, carotenoids, vitamins, phenolic compounds, amino acids, peptides, and proteins. Based on the research presented in this review, a proper diet that preserves cognitive function has the potential to improve age-related cognitive decline, Alzheimer's disease, and Parkinson's disease. Hopefully, this review will help to trigger the development of new foods and technologies that improve aging and cognitive functions and extend the healthy life span.

Repeated administration of inorganic nitrate on blood pressure and arterial stiffness: a systematic review and meta-analysis of randomized controlled trials

OBJECTIVE

We aim to synthesize effects of repeated administration (≥3 days) of inorganic nitrate on blood pressure and arterial stiffness measures.

METHODS

We conducted a systematic review and meta-analysis of randomized controlled trials with at least 3 days treatment of inorganic nitrate on blood pressure and arterial stiffness in individuals with or without elevated cardiovascular disease risk. MEDLINE, EMBASE and the Cochrane Library were searched through 2 July 2019. Two independent reviewers extracted relevant study data. Data were pooled using the generic inverse variance method with random-effects model, and expressed as mean differences with 95% confidence intervals. Certainty in the evidence was assessed using GRADE.

RESULTS

Forty-seven trials were included (n = 1101). Administration of inorganic nitrate significantly lowered SBP [mean difference: -2.91 mmHg, 95% confidence interval (95% CI): -3.92 to -1.89, I = 76%], DBP (mean difference: -1.45 mmHg, 95% CI: -2.22 to -0.68, I = 78%], central SBP (mean difference: -1.56 mmHg, 95% CI: -2.62 to -0.50, I = 30%) and central DBP (mean difference: -1.99 mmHg, 95% CI: -2.37 to -1.60, I = 0%). There was no effect on 24-h blood pressure, augmentation index or pulse wave velocity. Certainty in the evidence was graded moderate for central blood pressure, pulse wave velocity and low for peripheral blood pressure, 24-h blood pressure and augmentation index.

CONCLUSION

Repeated administration (≥3 days) of inorganic nitrate lower peripheral and central blood pressure. Results appear to be driven by beneficial effects in healthy and hypertensive individuals. More studies are required to increase certainty in the evidence.

The effect of beetroot inorganic nitrate supplementation on cardiovascular risk factors: A systematic review and meta-regression of randomized controlled trials

OBJECTIVES

Inorganic nitrate is one of the most effective compounds in beetroot for improving cardiovascular function due to its conversion to nitric oxide in the body. This review and meta-analysis aimed to investigate the role of beetroot inorganic nitrate supplementation on adults' cardiovascular risk factors.

METHODS

We conducted a systematic literature review of articles published without time limitation until November 2020 in PubMed, Embase, ISI Web of Science, Scopus, Cochrane Library, and gray literature databases. We included the original randomized clinical trials (RCTs) in which the effect of beetroot inorganic nitrate supplementation on endothelial function, arterial stiffness, and blood pressure was studied.

RESULTS

43 studies were included for qualitative synthesis, out of which 27 were eligible for meta-analysis. Beetroot inorganic nitrate supplementation significantly decreased Arterial Stiffness (Pulse Wave Velocity (-0.27 m/s, p = 0.04)) and increased Endothelial function (Flow Mediated Dilation: 0.62%, p = 0.002) but did not change other parameters (p > 0.05).

CONCLUSION

Beetroot inorganic nitrate supplementation might have a beneficial effect on cardiovascular risk factors. Further high-quality investigations will be needed to provide sufficient evidence.

Dietary nitrate and population health: a narrative review of the translational potential of existing laboratory studies

BACKGROUND

Dietary inorganic nitrate (NO3-) is a polyatomic ion, which is present in large quantities in green leafy vegetables and beetroot, and has attracted considerable attention in recent years as a potential health-promoting dietary compound. Numerous small, well-controlled laboratory studies have reported beneficial health effects of inorganic NO3- consumption on blood pressure, endothelial function, cerebrovascular blood flow, cognitive function, and exercise performance. Translating the findings from small laboratory studies into 'real-world' applications requires careful consideration.

MAIN BODY

This article provides a brief overview of the existing empirical evidence basis for the purported health-promoting effects of dietary NO3- consumption. Key areas for future research are then proposed to evaluate whether promising findings observed in small animal and human laboratory studies can effectively translate into clinically relevant improvements in population health. These proposals include: 1) conducting large-scale, longer duration trials with hard clinical endpoints (e.g. cardiovascular disease incidence); 2) exploring the feasibility and acceptability of different strategies to facilitate a prolonged increase in dietary NO3- intake; 3) exploitation of existing cohort studies to explore associations between NO3- intake and health outcomes, a research approach allowing larger samples sizes and longer duration follow up than is feasible in randomised controlled trials; 4) identifying factors which might account for individual differences in the response to inorganic NO3- (e.g. sex, genetics, habitual diet) and could assist with targeted/personalised nutritional interventions; 5) exploring the influence of oral health and medication on the therapeutic potential of NO3- supplementation; and 6) examining potential risk of adverse events with long term high- NO3- diets.

CONCLUSION

The salutary effects of dietary NO3- are well established in small, well-controlled laboratory studies. Much less is known about the feasibility and efficacy of long-term dietary NO3- enrichment for promoting health, and the factors which might explain the variable responsiveness to dietary NO3- supplementation between individuals. Future research focussing on the translation of laboratory data will provide valuable insight into the potential applications of dietary NO3- supplementation to improve population health.

Current Knowledge on Beetroot Bioactive Compounds: Role of Nitrate and Betalains in Health and Disease

An increase in the prevalence of noncommunicable chronic diseases has been occurring in recent decades. Among the deaths resulting from these conditions, cardiovascular diseases (CVD) stand out as the main contributors. In this regard, dietary patterns featuring a high content of vegetables and fruits, such as the Mediterranean and the DASH diets, are considered beneficial, and thus have been extensively studied. This has resulted in growing interest in vegetable-derived ingredients and food-supplements that may have potential therapeutic properties. Among these supplements, beetroot juice, which is obtained from the root vegetable Beta vulgaris, has gained much attention. Although a significant part of the interest in beetroot juice is due to its nitrate (NO₃^-) content, which has demonstrated bioactivity in the cardiovascular system, other ingredients with potential beneficial properties such as polyphenols, pigments and organic acids are also present. In this context, the aim of this review article is to analyze the current knowledge regarding the benefits related to the consumption of beetroot and derived food-supplements. Therefore, this article focuses on nitrate and betalains, which are considered to be the major bioactive compounds present in beetroot, and thus in the derived dietary supplements.

Effects of raw red beetroot consumption on metabolic markers and cognitive function in type 2 diabetes patients

OBJECTIVES

This study aimed to investigate the effects of raw red beetroot consumption on metabolic markers and cognitive function in type 2 diabetes patients.

METHODS

In a quasi-experimental study, 44 type 2 diabetes patients (57 ± 4.5 years) consumed raw red beetroot (100 g, daily), for 8 weeks. Metabolic markers including body weight, glucose and lipid profile parameters, inflammatory and oxidative stress markers, paraoxonase-1 activity, hepatic enzymes, blood pressure and cognitive function were measured at the beginning and end of 8 weeks.

RESULTS

Raw red beetroot consumption resulted in a significant decrease in fasting blood sugar (FBS) levels (-13.53 mg/dL), glycosylated hemoglobin (HbA1c)(-0.34%), apolipoproteinB100 (ApoB100) (-8.25 mg/dl), aspartate aminotransferase (AST) (-1.75 U/L), alanine aminotransferase (ALT) (-3.7 U/L), homocysteine (-7.88 μmol/l), systolic (-0.73 mmHg) and diastolic blood pressure (-0.34 mmHg), anda significant increase in total antioxidant capacity (TAC) (105 μmol/L) and cognitive function tests (all P values <0.05). Other variables did not change significantly after the intervention.

CONCLUSIONS

Raw red beetroot consumption for 8 weeks in T2DM patients has beneficial impacts on cognitive function, glucose metabolism and other metabolic markers.

Effect of inorganic nitrate supplementation on blood pressure in older adults: A systematic review and meta-analysis

BACKGROUND

Previous clinical studies have shown controversial results regarding the effect of inorganic nitrate supplementation on blood pressure (BP) in older individuals. We performed this systematic review and meta-analysis to assess the effect of inorganic nitrate on BP in older adults.

METHODS

Eligible studies were searched in Cochrane Library, PubMed, Scopus, Web of Science, and Embase. Randomized controlled trials which evaluated the effect of inorganic nitrate consumption on BP in older adults were recruited. The random-effect model was used to calculate the pooled effect sizes.

RESULTS

22 studies were included in this meta-analysis. Overall, inorganic nitrate consumption significantly reduced systolic blood pressure (SBP) by -3.90 mmHg (95% confidence interval: -5.23 to -2.57; P < 0.001) and diastolic blood pressure (DBP) by -2.62 mmHg (95% confidence interval: -3.86 to -1.37; P < 0.005) comparing with the control group. Subgroup analysis showed that the BP was significantly reduced when participants' age≥65, BMI>30, or baseline BP in prehypertension stage. And both SBP and DBP decreased significantly after acute nitrate supplementation of a single dose (<1 day) or more than 1-week. However, participants with hypertension at baseline were not associated with significant changes in both SBP and DBP. Subgroup analysis of measurement methods showed that only the resting BP group showed a significant reduction in SBP and DBP, compared with the 24-h ambulatory BP monitoring (ABPM) group and daily home BP measurement group.

CONCLUSION

These results demonstrate that consuming inorganic nitrate can significantly reduce SBP and DBP in older adults, especially in whose age ≥ 65, BMI＞30, or baseline BP in prehypertension stage.

Multiple-day high-dose beetroot juice supplementation does not improve pulmonary or muscle deoxygenation kinetics of well-trained cyclists in normoxia and hypoxia

Dietary nitrate (NO₃^-) supplementation via beetroot juice (BR) has been reported to lower oxygen cost (i.e., increased exercise efficiency) and speed up oxygen uptake (VO₂) kinetics in untrained and moderately trained individuals, particularly during conditions of low oxygen availability (i.e., hypoxia). However, the effects of multiple-day, high dose (12.4 mmol NO_3- per day) BR supplementation on exercise efficiency and VO₂ kinetics during normoxia and hypoxia in well-trained individuals are not resolved. In a double-blinded, randomized crossover study, 12 well-trained cyclists (66.4 ± 5.3 ml min^-1∙kg^-1) completed three transitions from rest to moderate-intensity (~70% of gas exchange threshold) cycling in hypoxia and normoxia with supplementation of BR or nitrate-depleted BR as placebo. Continuous measures of VO₂ and muscle (vastus lateralis) deoxygenation (ΔHHb, using near-infrared spectroscopy) were acquired during all transitions. Kinetics of VO₂ and deoxygenation (ΔHHb) were modeled using mono-exponential functions. Our results showed that BR supplementation did not alter the primary time constant for VO₂ or ΔHHb during the transition from rest to moderate-intensity cycling. While BR supplementation lowered the amplitude of the VO₂ response (2.1%, p = 0.038), BR did not alter steady state VO₂ derived from the fit (p = 0.258), raw VO₂ data (p = 0.231), moderate intensity exercise efficiency (p = 0.333) nor steady state ΔHHb (p = 0.224). Altogether, these results demonstrate that multiple-day, high-dose BR supplementation does not alter exercise efficiency or oxygen uptake kinetics during normoxia and hypoxia in well-trained athletes.

Dose-Response Effect of Dietary Nitrate on Muscle Contractility and Blood Pressure in Older Subjects: A Pilot Study

We have recently demonstrated that dietary nitrate, a source of nitric oxide (NO) via the nitrate → nitrite → NO enterosalivary pathway, can improve muscle contractility in healthy older men and women. Nitrate ingestion has also been shown to reduce blood pressure in some, but not all, studies of older individuals. However, the optimal dose for eliciting these beneficial effects is unknown. A pilot randomized, double-blind, placebo-controlled crossover study was therefore performed to determine the effects of ingesting 3.3 mL/kg of concentrated beetroot juice containing 0, 200, or 400 µmol/kg of nitrate in 9 healthy older subjects (mean age 70 ± 1 years). Maximal knee extensor power (Pmax) and speed (Vmax) were measured ~2.5 hours after nitrate ingestion using isokinetic dynamometry. Blood pressure was monitored periodically throughout each study. Pmax (in W/kg) was higher (p < .05) after the lower dose (3.9 ± 0.4) compared to the placebo (3.7 ± 0.4) or higher dose (3.7 ± 0.4). Vmax (in rad/s) also tended to be higher (p = .08) after the lower dose (11.9 ± 0.7) compared to the placebo (10.8 ± 0.8) or higher dose (11.2 ± 0.8). Eight out of 9 subjects achieved a higher Pmax and Vmax after the lower versus the higher dose. These dose-related changes in muscle contractility generally paralleled changes in breath NO levels. No significant changes were found in systolic, diastolic, or mean arterial blood pressure. A lower dose of nitrate increases muscle speed and power in healthy older individuals, but these improvements are lost at a higher dose. Blood pressure, on the other hand, is not reduced even with a higher dose.

Network analysis of nitrate-sensitive oral microbiome reveals interactions with cognitive function and cardiovascular health across dietary interventions

Many oral bacteria reduce inorganic nitrate, a natural part of a vegetable-rich diet, into nitrite that acts as a precursor to nitric oxide, a regulator of vascular tone and neurotransmission. Aging is hallmarked by reduced nitric oxide production with associated detriments to cardiovascular and cognitive function. This study applied a systems-level bacterial co-occurrence network analysis across 10-day dietary nitrate and placebo interventions to test the stability of relationships between physiological and cognitive traits and clusters of co-occurring oral bacteria in older people. Relative abundances of Proteobacteria increased, while Bacteroidetes, Firmicutes and Fusobacteria decreased after nitrate supplementation. Two distinct microbiome modules of co-occurring bacteria, that were sensitive to nitrate supplementation, showed stable relationships with cardiovascular (Rothia-Streptococcus) and cognitive (Neisseria-Haemophilus) indices of health across both dietary conditions. A microbiome module (Prevotella-Veillonella) that has been associated with pro-inflammatory metabolism was diminished after nitrate supplementation, including a decrease in relative abundance of pathogenic Clostridium difficile. These nitrate-sensitive oral microbiome modules are proposed as potential pre- and probiotic targets to ameliorate age-induced impairments in cardiovascular and cognitive health.

Acceptability and Feasibility of a 13-Week Pilot Randomised Controlled Trial Testing the Effects of Incremental Doses of Beetroot Juice in Overweight and Obese Older Adults

Nitrate-rich food can increase nitric oxide production and improve vascular and brain functions. This study examines the feasibility of a randomised controlled trial (RCT) testing the effects of prolonged consumption of different doses of dietary nitrate (NO3-) in the form of beetroot juice (BJ) in overweight and obese older participants. A single-blind, four-arm parallel pilot RCT was conducted in 62 overweight and obese (30.4 ± 4 kg/m2) older participants (mean ± standard deviation (SD), 66 ± 4 years). Participants were randomized to: (1) high-NO3- (HN: 2 × 70 mL BJ/day) (2) medium-NO3- (MN: 70 mL BJ/day), (3) low-NO3- (LN: 70 mL BJ on alternate days) or (4) Placebo (PL: 70 mL of NO3--depleted BJ on alternate days), for 13 weeks. Compliance was checked by a daily log of consumed BJ, NO3- intake, and by measuring NO3- and NO2- concentrations in plasma, saliva, and urine samples. Fifty participants completed the study. Self-reported compliance to the interventions was >90%. There were significant positive linear relationships between NO3- dose and the increase in plasma and urinary NO3- concentration (R2 = 0.71, P < 0.001 and R2 = 0.46 P < 0.001, respectively), but relationships between NO3- dose and changes in salivary NO3- and NO2- were non-linear (R2 = 0.35, P = 0.002 and R2 = 0.23, P = 0.007, respectively). The results confirm the feasibility of prolonged BJ supplementation in older overweight and obese adults.

Effects of Chewing Gum on Nitric Oxide Metabolism, Markers of Cardiovascular Health and Neurocognitive Performance after a Nitrate-Rich Meal

OBJECTIVES

Cardiovascular and neurocognitive responses to chewing gum have been reported, but the mechanisms are not well understood. Chewing gum after a nitrate-rich meal may upregulate the reduction of oral nitrate to nitrite and increase nitric oxide (NO), a molecule important to cardiovascular and neurocognitive health. We aimed to explore effects of chewing gum after a nitrate-rich meal on nitrate metabolism (through the enterosalivary nitrate-nitrite-NO pathway), endothelial function, blood pressure (BP), neurocognitive performance, mood and anxiety.

METHODS

Twenty healthy men (n = 6) and women (n = 14) with a mean age of 48 years (range: 23-69) were recruited to a randomized controlled cross-over trial. After consumption of a nitrate-rich meal (180 mg of nitrate), we assessed the acute effects of chewing gum, compared to no gum chewing, on (i) salivary nitrate, nitrite and the nitrate reductase ratio (100 x [nitrite]/([nitrate] + [nitrite]); (ii) plasma nitrite, S-nitrosothiols and other nitroso species (RXNO); (iii) endothelial function (measured by flow mediated dilatation); (iv) BP; (v) neurocognitive performance; (vi) mood; and (vii) anxiety.

RESULTS

Consumption of the nitrate-rich meal resulted in a significant increase in markers of nitrate metabolism. A significantly higher peak flow mediated dilatation was observed with chewing compared to no chewing (baseline adjusted mean difference: 1.10%, 95% CI: 0.06, 2.14; p = 0.038) after the nitrate-rich meal. A significant small increase in systolic BP, diastolic BP and heart rate were observed with chewing compared to no chewing after the nitrate-rich meal. The study did not observe increased oral reduction of nitrate to nitrite and NO, or improvements in neurocognitive performance, mood or anxiety with chewing compared to no chewing.

CONCLUSION

Chewing gum after a nitrate-rich meal resulted in an acute improvement in endothelial function and a small increase in BP but did not result in acute effects on neurocognitive function, mood or anxiety.