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

Investigating the association between nitrate dosing and nitrite generation by the human oral microbiota in continuous culture

The generation of nitrite by the oral microbiota is believed to contribute to healthy cardiovascular function, with oral nitrate reduction to nitrite associated with systemic blood pressure regulation. There is the potential to manipulate the composition or activities of the oral microbiota to a higher nitrate-reducing state through nitrate supplementation. The current study examined microbial community composition and enzymatic responses to nitrate supplementation in sessile oral microbiota grown in continuous culture. Nitrate reductase (NaR) activity and nitrite concentrations were not significantly different to tongue-derived inocula in model biofilms. These were generally dominated by Streptococcus spp., initially, and a single nitrate supplementation resulted in the increased relative abundance of the nitrate-reducing genera Veillonella, Neisseria, and Proteus spp. Nitrite concentrations increased concomitantly and continued to increase throughout oral microbiota development. Continuous nitrate supplementation, over a 7-day period, was similarly associated with an elevated abundance of nitrate-reducing taxa and increased nitrite concentration in the perfusate. In experiments in which the models were established in continuous low or high nitrate environments, there was an initial elevation in nitrate reductase, and nitrite concentrations reached a relatively constant concentration over time similar to the acute nitrate challenge with a similar expansion of Veillonella and Neisseria. In summary, we have investigated nitrate metabolism in continuous culture oral biofilms, showing that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of putatively NaR-producing taxa.IMPORTANCEClinical evidence suggests that blood pressure regulation can be promoted by nitrite generated through the reduction of supplemental dietary nitrate by the oral microbiota. We have utilized oral microbiota models to investigate the mechanisms responsible, demonstrating that nitrate addition increases nitrate reductase activity and nitrite concentrations in oral microbiota with the expansion of nitrate-reducing taxa.

Effects of dietary inorganic nitrate on blood pressure during and post-exercise recovery: A systematic review and meta-analysis of randomized placebo-controlled trials

OBJECTIVES

A systematic review with meta-analysis was completed to study the effects of dietary inorganic nitrate (NO3-) oral ingestion from vegetables and salts on blood pressure responses during and following exercise.

BACKGROUND

NO3- is a hypotensive agent with the potential to reduce blood pressure peaks during exercise and amplify exercise-induced hypotensive effects. Several randomized and controlled trials have investigated the effects of NO3- on hemodynamic responses to physical exercise, however this still has yet to be studied systematically.

METHODS

The searches were conducted on EMBASE, Medline, and SPORTSDiscus databases. The study included masked randomized controlled trials (RCTs) with participants ≥18 years old. The NO3-intervention group received at least 50 mg NO3-/day with similar sources amid NO3- and placebo conditions. Included studies reported systolic blood pressure (SBP) or diastolic blood pressure (DBP) values during or following exercise performance.

RESULTS

1903 studies were identified, and twenty-six achieved the inclusion criteria. NO3- daily dosages ranged from 90 to 800 mg/day. Throughout exercise, SBP had smaller increases in the NO3- group (-2.81 mmHg (95%CI: -5.20 to -0.41), p=0.02. DBP demonstrated lower values in the NO3- group (-2.41 mmHg (95%CI: -4.02 to -0.79), p=0.003. In the post-exercise group, the NO3- group presented lower SBP values (-3.53 mmHg (95%CI: -5.65 to 1.41), p=0.001, while no changes were identified in DBP values between NO3- and placebo groups (p=0.31). Subgroup meta-analysis revealed that SBP baseline values, exercise type, duration of NO3- ingestion, and its dosages mediated blood pressure responses during and following exercise.

CONCLUSIONS

NO3- ingestion prior to exercise attenuated the increases in SBP and DBP during exercise, and increased the decline in SBP after exercise. These results are dependent on factors that moderate the blood pressure responses (e.g., health status, type of exercise, resting blood pressure values).

Oral nitrate supplementation improves cardiovascular risk markers in COPD: ON-BC, a randomised controlled trial

BACKGROUND

Short-term studies suggest that dietary nitrate (NO3 -) supplementation may improve the cardiovascular risk profile, lowering blood pressure (BP) and enhancing endothelial function. It is not clear if these beneficial effects are sustained and whether they apply in people with COPD, who have a worse cardiovascular profile than those without COPD. Nitrate-rich beetroot juice (NR-BRJ) is a convenient dietary source of nitrate.

METHODS

The ON-BC trial was a randomised, double-blind, placebo-controlled parallel group study in stable COPD patients with home systolic BP (SBP) measurement ≥130 mmHg. Participants were randomly allocated (1:1) using computer-generated, block randomisation to either 70 mL NR-BRJ (400 mg NO3 -) (n=40) or an otherwise identical nitrate-depleted placebo juice (0 mg NO3 -) (n=41), once daily for 12 weeks. The primary end-point was between-group change in home SBP measurement. Secondary outcomes included change in 6-min walk distance (6MWD) and measures of endothelial function (reactive hyperaemia index (RHI) and augmentation index normalised to a heart rate of 75 beats·min-1 (AIx75)) using an EndoPAT device. Plasma nitrate and platelet function were also measured.

RESULTS

Compared with placebo, active treatment lowered SBP (Hodges-Lehmann treatment effect -4.5 (95% CI -5.9- -3.0) mmHg), and improved 6MWD (30.0 (95% CI 15.7-44.2) m; p<0.001), RHI (0.34 (95% CI 0.03-0.63); p=0.03) and AIx75 (-7.61% (95% CI -14.3- -0.95%); p=0.026).

CONCLUSIONS

In people with COPD, prolonged dietary nitrate supplementation in the form of beetroot juice produces a sustained reduction in BP, associated with an improvement in endothelial function and exercise capacity.

The Role of Diet in the Prevention of Hypertension and Management of Blood Pressure: An Umbrella Review of Meta-Analyses of Interventional and Observational Studies

High blood pressure (BP) is a major pathological risk factor for the development of several cardiovascular diseases. Diet is a key modifier of BP, but the underlying relationships are not clearly demonstrated. This is an umbrella review of published meta-analyses to critically evaluate the wide range of dietary evidence from bioactive compounds to dietary patterns on BP and risk of hypertension. PubMed, Embase, Web of Science, and Cochrane Central Register of Controlled Trials were searched from inception until October 31, 2021, for relevant meta-analyses of randomized controlled trials or meta-analyses of observational studies. A total of 175 publications reporting 341 meta-analyses of randomized controlled trials (145 publications) and 70 meta-analyses of observational studies (30 publications) were included in the review. The methodological quality of the included publications was assessed using Assessment of Multiple Systematic Reviews 2 and the evidence quality of each selected meta-analysis was assessed using NutriGrade. This umbrella review supports recommended public health guidelines for prevention and control of hypertension. Dietary patterns including the Dietary Approaches to Stop Hypertension and the Mediterranean-type diets that further restrict sodium, and moderate alcohol intake are advised. To produce high-quality evidence and substantiate strong recommendations, future research should address areas where the low quality of evidence was observed (for example, intake of dietary fiber, fish, egg, meat, dairy products, fruit juice, and nuts) and emphasize focus on dietary factors not yet conclusively investigated.

Dietary Nitrate from Plant Foods: A Conditionally Essential Nutrient for Cardiovascular Health

Under specific conditions, such as catabolic stress or systemic inflammation, endogenous nutrient production becomes insufficient and exogenous supplementation (for example, through dietary intake) is required. Herein, we propose consideration of a dietary nitrate from plant foods as a conditionally essential nutrient for cardiovascular health based on its role in nitric oxide homeostasis. Nitrate derived from plant foods may function as a conditionally essential nutrient, whereas nitrate obtained from other dietary sources, such as drinking water and cured/processed meats, warrants separate consideration because of the associated health risks. We have surveyed the literature and summarized epidemiological evidence regarding the effect of dietary nitrate on cardiovascular disease and risk factors. Meta-analyses and population-based observational studies have consistently demonstrated an inverse association of dietary nitrate with blood pressure and cardiovascular disease outcomes. Considering the available evidence, we suggest 2 different approaches to providing dietary guidance on nitrate from plant-based dietary sources as a nutrient: the Dietary Reference Intakes developed by the National Academies of Sciences, Engineering, and Medicine, and the dietary guidelines evaluated by the Academy of Nutrition and Dietetics. Ultimately, this proposal underscores the need for food-based dietary guidelines to capture the complex and context-dependent relationships between nutrients, particularly dietary nitrate, and health.

Should the non-canonical pathway of nitric oxide generation be targeted in hypertensive pregnancies?

Hypertension in pregnancy is prevalent, affecting around 10% of pregnancies worldwide, and significantly increases the risk of adverse outcomes for both mothers and their babies. Current treatment strategies for pregnant women with hypertension are limited, and new approaches for the management of hypertension in pregnancy are urgently needed. Substantial evidence from non-pregnant subjects has demonstrated the potential for dietary nitrate supplementation to increase nitric oxide (NO) bioavailability and lower blood pressure, following bioactivation via the non-canonical NO pathway. Emerging data suggest this approach may also be of benefit in pregnant women, although studies are limited. This review aims to summarise the current evidence from preclinical and clinical studies of nitrate supplementation in pregnancy, drawing on data from non-pregnant populations where appropriate and highlighting key gaps in knowledge that remain to be addressed in future trials.

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

Short-Term L-Citrulline Supplementation Does Not Affect Blood Pressure, Pulse Wave Reflection, or Arterial Stiffness at Rest and during Isometric Exercise in Older Males

Hypertension and arterial stiffness are significant factors contributing to cardiovascular disease. L-citrulline, a nitric oxide precursor, has been proposed as a nutritional, non-pharmacological blood pressure-lowering intervention. This study aimed to investigate the impact of L-citrulline on central and peripheral blood pressure, pulse wave reflection, and central arterial stiffness at rest and during an isometric knee extension exercise protocol. Twelve older males received 6 g of L-citrulline or a placebo for six days using a double-blind crossover design. Blood hemodynamics parameters (i.e., aortic and brachial systolic and diastolic blood pressure, mean arterial pressure, pulse pressure, heart rate), pulse wave reflection (i.e., augmented pressure, augmentation index, forward/backward wave pressure), and arterial stiffness (i.e., carotid-femoral pulse wave velocity) were measured at baseline, post-supplementation, and during isometric exercise. No significant effects of L-citrulline supplementation were observed at rest or during exercise on blood pressure, pulse wave reflection, or arterial stiffness. Both central and peripheral blood pressure were increased during the exercise, which is consistent with isometric contractions. The results of the present study do not support any blood pressure-lowering effect of short-term L-citrulline at rest or during low-intensity isometric exercise compared to the pre-exercise values in older males.

Moderate doses of dietary nitrate elicit greater effects on blood pressure and endothelial function than a high dose: A 13-week pilot study

BACKGROUND & AIMS

Few studies have explored the prolonged effects of dietary nitrate on vascular health. This pilot study tested the effects of prolonged consumption (13 weeks) of a range of doses of dietary nitrate (NO₃^-), provided as beetroot juice (BJ), on blood pressure (BP) and endothelial function in overweight and obese older participants.

METHODS AND RESULTS

Sixty-two overweight or obese older participants (60-75 years) were randomized to the following interventions: (1) high NO₃^- (2) medium NO₃^-, (3) low NO₃^-, or (4) placebo. Resting clinic and home BP were measured pre- and post-intervention. Laser Doppler iontophoresis was used to quantify changes in endothelial-dependent and independent microvascular blood flow.

RESULTS

This pilot study showed that medium and low doses of NO₃^- were more effective in lowering resting-clinic SBP (P = 0.04 and, P = 0.03, respectively) than was PL. The lower doses of NO₃^- also resulted in significant increases in microvascular perfusion (medium, P = 0.02; low, P = 0.002) relative to baseline values.

CONCLUSION

These findings indicate that supplementation with medium and low, but not high, doses of NO₃^- for 13 weeks had positive effects on BP and endothelial function in older overweight and obese adults. These findings require confirmation in larger studies.

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.

Regulatory effect of dietary nitrate on blood pressure: a meta-analysis of randomized controlled trials

Hypertension is the leading risk factor for global disease burden. Many clinical studies have reported that dietary inorganic nitrate can affect blood pressure. In this study, the PubMed, Embase, and Cochrane Library databases were searched for relevant literature published before December 2021 to explore the preventive and therapeutic effects of inorganic nitrate on hypertension. Two reviewers evaluated the randomized controlled trials of inorganic nitrates. This study included a total of 19 articles. The analyzed outcomes of the study were systolic, diastolic and mean arterial blood pressures as well as 24-hour ambulatory blood pressure. RevMan 5.4 was used to conduct meta-analysis. In the healthy population, inorganic nitrate lowered systolic blood pressure (-2.42 mmHg, 95% confidence intervals (CI) [-4.28, -0.57]; P = 0.01) but not diastolic blood pressure (-0.58 mmHg, 95% CI [-1.84, 0.68]; P = 0.36) or mean arterial pressure (-1.01 mmHg, 95% CI [-3.55, 1.54]; P = 0.44). However, in the hypertensive population, inorganic nitrates did not lower systolic blood pressure (-0.82 mmHg, 95% CI [-2.53, 0.90]; P = 0.35), diastolic blood pressure (-0.03 mmHg, 95% CI [-1.35, 1.30]; P = 0.97), 24-hour ambulatory systolic blood pressure (-0.22 mmHg, 95% CI [-1.50, 1.94]; P = 0.8), or 24-hour ambulatory diastolic blood pressure (-0.33 mmHg, 95% CI [-2.03, 1.37]; P = 0.7). In conclusion, inorganic nitrate can mildly reduce systolic blood pressure in healthy people, but does not have a lowering effect on blood pressure in patients with hypertension. Further research is required to obtain more definitive data and prove the link between inorganic nitrate and blood pressure.

Concurrent dietary intake to nitrate, thiocyanate, and perchlorate is negatively associated with hypertension in adults in the USA

We aimed to comprehensively evaluate the association of urinary nitrate, thiocyanate, and perchlorate metabolites with hypertension among a nationally representative sample of the US adult population. This cross-sectional study investigated data from 15,717 adults aged more than 20 years obtained from the National Health and Nutritional Examination Survey (NHANES) for the years 2005-2016. In the survey, urinary levels of nitrate, thiocyanate, and perchlorate were measured using ion chromatography combined with electrospray tandem mass spectrometry. Blood pressure was calculated as the mean of three measurements. Hypertension was defined as (a) systolic BP ≥130 and/or diastolic BP ≥80 mmHg and/or (b) self-report. Multivariate logistic regression and weighted quantile sum (WQS) regression models were applied to estimate the association between exposure to multiple inorganic anions and hypertension. Restricted cubic spline (RCS) regressions were fitted to discern the potential relationship between the anion exposure and hypertension. These innovation methods used to support our results. Overall, 7533 (49.95%) people with and 7638 (50.35%) without hypertension were included in this study. In the multivariable-adjusted logistic regression models, urinary nitrate (P < 0.001) and perchlorate (P < 0.001) were independently negatively associated with increased occurrence of hypertension, while urinary thiocyanate was insignificantly associated with hypertension (P = 0.664). The WQS regression index showed that, in combination, the three inorganic anions mixture were negatively correlated with hypertension (adjusted OR 0.89; 95% CI 0.83-0.95, P < 0.001). Urinary nitrate was the most heavily weighted component in the hypertension model (weight = 0.784). RCS regression demonstrated that nitrate (nonlinearity P = 0.205) and perchlorate (nonlinearity P = 0.701) were linearly associated with decreased occurrence of hypertension. Concurrent exposure to nitrate, thiocyanate, and perchlorate is associated with a decreased risk of hypertension, with the greatest influence coming from nitrate probably; urinary specific thiocyanate alone had an insignificant association with hypertension.

Supplementation with Nitric Oxide Precursors for Strength Performance: A Review of the Current Literature

Nitric-oxide-stimulating dietary supplements are widely available and marketed to strength athletes and weightlifters seeking to increase muscle performance and augment training adaptations. These supplements contain ingredients classified as nitric oxide (NO) precursors (i.e., "NO boosters"). Endogenous NO is generated via a nitric oxide synthase (NOS)-dependent pathway and a NOS-independent pathway that rely on precursors including L-arginine and nitrates, with L-citrulline serving as an effective precursor of L-arginine. Nitric oxide plays a critical role in endothelial function, promoting relaxation of vascular smooth muscle and subsequent dilation which may favorably impact blood flow and augment mechanisms contributing to skeletal muscle performance, hypertrophy, and strength adaptations. The aim of this review is to describe the NO production pathways and summarize the current literature on the effects of supplementation with NO precursors for strength and power performance. The information will allow for an informed decision when considering the use of L-arginine, L-citrulline, and nitrates to improve muscular function by increasing NO bioavailability.

Factors that Moderate the Effect of Nitrate Ingestion on Exercise Performance in Adults: A Systematic Review with Meta-Analyses and Meta-Regressions

To identify how variables such as exercise condition, supplementation strategy, participant characteristics and demographics, and practices that control oral microbiota diversity could modify the effect of inorganic nitrate ingestion (as nitrate salt supplements, beetroot juice, and nitrate-rich vegetables) on exercise performance, we conducted a systematic review with meta-analysis. Studies were identified in PubMed, Embase, and Cochrane databases. Eligibility criteria included randomized controlled trials assessing the effect of inorganic nitrate on exercise performance in healthy adults. To assess the variation in effect size, we used meta-regression models for continuous variables and subgroup analysis for categorical variables. A total of 123 studies were included in this meta-analysis, comprising 1705 participants. Nitrate was effective for improving exercise performance (standardized mean difference [SMD]: 0.101; 95% CI: 0.051, 0.151, P <0.001, I2 = 0%), although nitrate salts supplementation was not as effective (P = 0.629) as ingestion via beetroot juice (P <0.001) or a high-nitrate diet (P = 0.005). Practices that control oral microbiota diversity influenced the nitrate effect, with practices harmful to oral bacteria decreasing the ergogenic effect of nitrate. The ingestion of nitrate was most effective for exercise lasting between 2 and 10 min (P <0.001). An inverse dose-response relation between the fraction of inspired oxygen and the effect size (coefficient: -0.045, 95% CI: -0.085, -0.005, P = 0.028) suggests that nitrate was more effective in increasingly hypoxic conditions. There was a dose-response relation for acute administration (P = 0.049). The most effective acute dose was between 5 and 14.9 mmol provided ≥150 min prior to exercise (P <0.001). An inverse dose-response for protocols ≥2 d was observed (P = 0.025), with the optimal dose between 5 and 9.9 mmol·d-1 (P <0.001). Nitrate, via beetroot juice or a high-nitrate diet, improved exercise performance, in particular, in sessions lasting between 2 and 10 min. Ingestion of 5-14.9 mmol⋅d-1 taken ≥150 min prior to exercise appears optimal for performance gains and athletes should be aware that practices controlling oral microbiota diversity may decrease the effect of nitrate.