Nitrate-rich beetroot juice offsets salivary acidity following carbohydrate ingestion before and after endurance exercise in healthy male runners

Nitrate ingestion blunts the increase in blood pressure during cool air exposure: a double-blind, placebo-controlled, randomized, crossover trial

Cold exposure increases blood pressure (BP) and salivary flow rate (SFR). Increased cold-induced SFR would be hypothesized to enhance oral nitrate delivery for reduction to nitrite by oral anaerobes and to subsequently elevate plasma [nitrite] and nitric oxide bioavailability. We tested the hypothesis that dietary nitrate supplementation would increase plasma [nitrite] and lower BP to a greater extent in cool compared with normothermic conditions. Twelve males attended the laboratory on four occasions. Baseline measurements were completed at 28°C. Subsequently, participants ingested 140 mL of concentrated nitrate-rich (BR; ∼13 mmol nitrate) or nitrate-depleted (PL) beetroot juice. Measurements were repeated over 3 h at either 28°C (Norm) or 20°C (Cool). Mean skin temperature was lowered compared with baseline in PL-Cool and BR-Cool. SFR was greater in BR-Norm, PL-Cool, and BR-Cool than PL-Norm. Plasma [nitrite] at 3 h was higher in BR-Cool (592 ± 239 nM) versus BR-Norm (410 ± 195 nM). Systolic BP (SBP) at 3 h was not different between PL-Norm (117 ± 6 mmHg) and BR-Norm (113 ± 9 mmHg). SBP increased above baseline at 1, 2, and 3 h in PL-Cool but not BR-Cool. These results suggest that BR consumption is more effective at increasing plasma [nitrite] in cool compared with normothermic conditions and blunts the rise in BP following acute cool air exposure, which might have implications for attenuating the increased cardiovascular strain in the cold.NEW & NOTEWORTHY Compared with normothermic conditions, acute nitrate ingestion increased plasma [nitrite], a substrate for oxygen-independent nitric oxide generation, to a greater extent during cool air exposure. Systolic blood pressure was increased during cool air exposure in the placebo condition with this cool-induced blood pressure increase attenuated after acute nitrate ingestion. These findings improve our understanding of environmental factors that influence nitrate metabolism and the efficacy of nitrate supplementation to lower blood pressure.

Effects of dietary nitrate supplementation on oral health and associated markers of systemic health: a systematic review

Poor oral health can impact an individual's ability to eat and has been associated with an increased risk of non-communicable diseases. While the benefits of nitrate consumption on oral health were first proposed more than 20 years ago, no systematic review has been published examining effects of dietary nitrate on oral health. This systematic review investigated the effects of dietary nitrate on markers of oral health in vivo in randomized controlled trials (RCTs). Five databases (PubMed, The Cochrane Library, CINAHL, MEDLINE, and SPORTDiscus) were searched from inception until March 2023. Nine articles reporting data on 284 participants were included. Dietary nitrate was provided via beetroot juice in most studies. The duration of the interventions ranged from one day to six weeks. Dietary nitrate supplementation increased the relative abundance of several individual bacterial genera including Neisseria and Rothia. Dietary nitrate supplementation increased salivary pH and decreased salivary acidification following consumption of a sugar-sweetened beverage. Furthermore, dietary nitrate supplementation resulted in a decrease in the gingival inflammation index. The results of this systematic review suggest that dietary nitrate could represent a potential nutritional strategy to positively modify oral health by impacting the oral microbiome, altering salivary pH, and minimizing gingival inflammation.

The effects of nitrate on the oral microbiome: a systematic review investigating prebiotic potential

Background

Nitrate (NO3-) has been suggested as a prebiotic for oral health. Evidence indicates dietary nitrate and nitrate supplements can increase the proportion of bacterial genera associated with positive oral health whilst reducing bacteria implicated in oral disease(s). In contrast, chlorhexidine-containing mouthwashes, which are commonly used to treat oral infections, promote dysbiosis of the natural microflora and may induce antimicrobial resistance.

Methods

A systematic review of the literature was undertaken, surrounding the effects of nitrate on the oral microbiota.

Results

Overall, n = 12 in vivo and in vitro studies found acute and chronic nitrate exposure increased (representatives of) health-associated Neisseria and Rothia (67% and 58% of studies, respectively) whilst reducing periodontal disease-associated Prevotella (33%). Additionally, caries-associated Veillonella and Streptococcus decreased (25% for both genera). Nitrate also altered oral microbiome metabolism, causing an increase in pH levels (n = 5), which is beneficial to limit caries development. Secondary findings highlighted the benefits of nitrate for systemic health (n = 5).

Conclusions

More clinical trials are required to confirm the impact of nitrate on oral communities. However, these findings support the hypothesis that nitrate could be used as an oral health prebiotic. Future studies should investigate whether chlorhexidine-containing mouthwashes could be replaced or complemented by a nitrate-rich diet or nitrate supplementation.

Does Co-Supplementation with Beetroot Juice and Other Nutritional Supplements Positively Impact Sports Performance?: A Systematic Review

In the pursuit of enhanced athletic prowess in different disciplines, athletes constantly look for strategies to increase their physical performance, encompassing technical skills and dietary components, which inevitably, in most cases, include the incorporation of sports supplements. In recent years, there has been an increase in the number of athletes using ergogenic aids. In this context, scientific evidence must play a prominent role in either endorsing or warning against the use of these products, ensuring the preservation of health while promoting the theoretically established positive benefits. In this vein, beetroot juice (BJ) stands out as a key supplement as an ergogenic aid to improve sports performance, given its demonstrated influence on both aerobic and anaerobic exercise. However, despite widespread global demand, there remains a lack of understanding regarding the potential synergistic effects of combining BJ with other supplements. Consequently, our study aims to determine whether the combination of BJ with another nutritional supplement can enhance its beneficial effects and, therefore, optimize physical performance in humans. A comprehensive literature search was conducted in two major databases-Web of Science and PubMed-from 1 January 2018 to 29 January 2023, using specific keywords. After the exclusion criteria, six articles were selected for analysis. Therefore, our study shows that the effectiveness of combining BJ with another supplement mainly depends on the duration of the chronic intervention, which is where the greatest benefits have been observed.

Nitrate and a nitrate-reducing Rothia aeria strain as potential prebiotic or synbiotic treatments for periodontitis

A few studies indicate that nitrate can reduce dysbiosis from a periodontitis point of view. However, these experiments were performed on samples from healthy individuals, and it is unknown if nitrate will be effective in periodontal patients, where the presence of nitrate-reducing bacteria is clearly reduced. The aim of this study was to test the effect of nitrate and a nitrate-reducing R. aeria (Ra9) on subgingival biofilms of patients with periodontitis. For this, subgingival plaque was incubated with 5 mM nitrate for 7 h (n = 20) or 50 mM nitrate for 12 h (n = 10), achieving a ~50% of nitrate reduction in each case. Additionally, Ra9 was combined with 5 mM nitrate (n = 11), increasing the nitrate reduced and nitrite produced (both p < 0.05). The addition of nitrate to periodontitis communities decreased biofilm mass (50 mM > 5 mM, both p < 0.05). Five millimolar nitrate, 50 mM nitrate and 5 mM nitrate + Ra9 led to 3, 28 and 20 significant changes in species abundance, respectively, which were mostly decreases in periodontitis-associated species. These changes led to a respective 15%, 63% (both p < 0.05) and 6% (not significant) decrease in the dysbiosis index. Using a 10-species biofilm model, decreases in periodontitis-associated species in the presence of nitrate were confirmed by qPCR (all p < 0.05). In conclusion, nitrate metabolism can reduce dysbiosis and biofilm growth of periodontitis communities. Five millimolar nitrate (which can be found in saliva after vegetable intake) was sufficient, while increasing this concentration to 50 mM (which could be achieved by topical applications such as a periodontal gel) increased the positive effects. Ra9 increased the nitrate metabolism of periodontitis communities and should be tested in vivo.

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.

The oral microbiome, nitric oxide and exercise performance

The human microbiome comprises ∼10¹³-10¹⁴ microbial cells which form a symbiotic relationship with the host and play a critical role in the regulation of human metabolism. In the oral cavity, several species of bacteria are capable of reducing nitrate to nitrite; a key precursor of the signaling molecule nitric oxide. Nitric oxide has myriad physiological functions, which include the maintenance of cardiovascular homeostasis and the regulation of acute and chronic responses to exercise. This article provides a brief narrative review of the research that has explored how diversity and plasticity of the oral microbiome influences nitric oxide bioavailability and related physiological outcomes. There is unequivocal evidence that dysbiosis (e.g. through disease) or disruption (e.g. by use of antiseptic mouthwash or antibiotics) of the oral microbiota will suppress nitric oxide production via the nitrate-nitrite-nitric oxide pathway and negatively impact blood pressure. Conversely, there is preliminary evidence to suggest that proliferation of nitrate-reducing bacteria via the diet or targeted probiotics can augment nitric oxide production and improve markers of oral health. Despite this, it is yet to be established whether purposefully altering the oral microbiome can have a meaningful impact on exercise performance. Future research should determine whether alterations to the composition and metabolic activity of bacteria in the mouth influence the acute responses to exercise and the physiological adaptations to exercise training.

On the Role of Dietary Nitrate in the Maintenance of Systemic and Oral Health

The assessment of the significance of nitrates ingested with food has undergone a fundamental change in recent years after many controversial discussions. While for a long time, a diet as low in nitrates as possible was advocated on the basis of epidemiological data suggesting a cancer-promoting effect of nitrate-rich diets, more recent findings show that dietary nitrate, after its conversion to nitrite by nitrate-reducing bacteria of the oral microbiota, is an indispensable alternative source for the formation of nitric oxide (NO), which comprises a key element in the physiology of a variety of central body functions such as blood pressure control, defense against invading bacteria and maintenance of a eubiotic microbiota in the gut and oral cavity. This compact narrative review aims to present the evidence supported by clinical and in vitro studies on the ambivalent nature of dietary nitrates for general and oral health and to explain how the targeted adjuvant use of nitrate-rich diets could open new opportunities for a more cause-related control of caries and periodontal disease.

The Importance of Nitrate Reduction for Oral Health

Salivary glands concentrate plasma nitrate into saliva, leading to high nitrate concentrations that can reach the millimolar range after a nitrate-rich vegetable meal. Whereas human cells cannot reduce nitrate to nitrite effectively, certain oral bacteria can. This leads to an increase in systemic nitrite that can improve conditions such as hypertension and diabetes through nitric oxide availability. Apart from systemic benefits, it has been proposed that microbial nitrate reduction can also promote oral health. In this review, we discuss evidence associating dietary nitrate with oral health. Oral bacteria can reduce nitrite to nitric oxide, a free radical with antimicrobial properties capable of inhibiting sensitive species such as anaerobes involved in periodontal diseases. Nitrate has also been shown to increase resilience against salivary acidification in vivo and in vitro, thus preventing caries development. One potential mechanism is proton consumption during denitrification and/or bacterial reduction of nitrite to ammonium. Additionally, lactic acid (organic acid involved in oral acidification) and hydrogen sulfide (volatile compound involved in halitosis) can act as electron donors for these processes. The nitrate-reducing bacteria Rothia and Neisseria are consistently found at higher levels in individuals free of oral disease (vs. individuals with caries, periodontitis, and/or halitosis) and increase when nitrate is consumed in clinical studies. Preliminary in vitro and clinical evidence show that bacteria normally associated with disease, such as Veillonella (caries) and Prevotella (periodontal diseases and halitosis), decrease in the presence of nitrate. We propose nitrate as an ecologic factor stimulating eubiosis (i.e., an increase in health-associated species and functions). Finally, we discuss the preventive and therapeutic potential, as well as safety issues, related to the use of nitrate. In vivo evidence is limited; therefore, robust clinical studies are required to confirm the potential benefits of nitrate reduction on oral health.

Body mass-normalized moderate dose of dietary nitrate intake improves endothelial function and walking capacity in patients with peripheral artery disease

Peripheral artery disease (PAD) is characterized by the accumulation of atherosclerotic plaques in the lower extremity conduit arteries, which impairs blood flow and walking capacity. Dietary nitrate has been used to reduce blood pressure (BP) and improve walking capacity in PAD. However, a standardized dose for PAD has not been determined. Therefore, we sought to determine the effects of a body mass-normalized moderate dose of nitrate (0.11 mmol nitrate/kg) as beetroot juice on serum nitrate/nitrite, vascular function, walking capacity, and tissue oxygen utilization capacity in patients with PAD. A total of 11 patients with PAD received either nitrate supplement or placebo in a randomized crossover design. Total serum nitrate/nitrite, resting BP, brachial and popliteal artery endothelial function (flow-mediated dilation, FMD), arterial stiffness (pulse-wave velocity, PWV), augmentation index (AIx), maximal walking distance and time, claudication onset time, and skeletal muscle oxygen utilization were measured pre- and postnitrate and placebo intake. There were significant group × time interactions (P < 0.05) for serum nitrate/nitrite, FMD, BP, walking distance and time, and skeletal muscle oxygen utilization. The nitrate group showed significantly increased serum nitrate/nitrite (Δ1.32 μM), increased brachial and popliteal FMD (Δ1.3% and Δ1.7%, respectively), reduced peripheral and central systolic BP (Δ-4.7 mmHg and Δ-8.2 mmHg, respectively), increased maximal walking distance (Δ92.7 m) and time (Δ56.3 s), and reduced deoxygenated hemoglobin during walking. There were no changes in PWV, AIx, or claudication (P > 0.05). These results indicate that a body-mass normalized moderate dose of nitrate may be effective and safe for reducing BP, improving endothelial function, and improving walking capacity in patients with PAD.

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.

A Single Dose of Nitrate Increases Resilience Against Acidification Derived From Sugar Fermentation by the Oral Microbiome

Tooth decay starts with enamel demineralization due to an acidic pH, which arises from sugar fermentation by acidogenic oral bacteria. Previous in vitro work has demonstrated that nitrate limits acidification when incubating complex oral communities with sugar for short periods (e.g., 1-5 h), driven by changes in the microbiota metabolism and/or composition. To test whether a single dose of nitrate can reduce acidification derived from sugar fermentation in vivo, 12 individuals received a nitrate-rich beetroot supplement, which was compared to a placebo in a blinded crossover setting. Sucrose-rinses were performed at baseline and 2 h after supplement or placebo intake, and the salivary pH, nitrate, nitrite, ammonium and lactate were measured. After nitrate supplement intake, the sucrose-induced salivary pH drop was attenuated when compared with the placebo (p < 0.05). Salivary nitrate negatively correlated with lactate production and positively with ΔpH after sucrose exposure (r= -0.508 and 0.436, respectively, both p < 0.05). Two additional pilot studies were performed to test the effect of sucrose rinses 1 h (n = 6) and 4 h (n = 6) after nitrate supplement intake. In the 4 h study, nitrate intake was compared with water intake and bacterial profiles were analysed using 16S rRNA gene Illumina sequencing and qPCR detection of Rothia. Sucrose rinses caused a significant pH drop (p < 0.05), except 1 h and 4 h after nitrate supplement intake. After 4 h of nitrate intake, there was less lactate produced compared to water intake (p < 0.05) and one genus; Rothia, increased in abundance. This small but significant increase was confirmed by qPCR (p < 0.05). The relative abundance of Rothia and Neisseria negatively correlated with lactate production (r = -0.601 and -0.669, respectively) and Neisseria positively correlated with pH following sucrose intake (r = 0.669, all p < 0.05). Together, these results show that nitrate can acutely limit acidification when sugars are fermented, which appears to result from lactate usage by nitrate-reducing bacteria. Future studies should assess the longitudinal impact of daily nitrate-rich vegetable or supplement intake on dental health.