Dietary Nitrate

ABSTRACT: Dietary nitrate has been demonstrated to have a range of beneficial vascular effects, including reducing blood pressure, reduction in pulse wave velocity, regulation of cerebral blood flow, enhancing exercise performance in healthy individuals, stimulating angiogenesis and vasculogenesis etc. Earlier studies with nitrate or nitrite also demonstrate the synergistic effects against ischaemia-reperfusion injury and reduce arterial stiffness, inflammation and intimal thickness. However, there is a need for scientific evidences for hard endpoints beyond epidemiological studies. Although studies have suggested reduction in cardiovascular risk and cancer with diets high in nitrate-rich vegetables but still a lot remains to be elucidated. Moreover various therapeutic effects have reported that the nitrate and nitrite have more affluent biological actions till now, and numerous attempts are currently ongoing for the consideration of potential useful effects in the clinical uses. Here we corroborated a brief data regarding clinical uses of nitrite and nitrate that may serve as potential therapeutic regimes.

Published studies were included in the analysis based on the following criteria: (1) investigated the association between dietary nitrate and/or nitrite intake and cancer risk; (2) had a case-control or cohort study design; (3) provided odds ratio (OR), relative risk (RR), or hazard ratio (HR) estimates with its 95%CI or data necessary to calculate them. When multiple publications from the same study were available, we used the publication with the largest number of cases or the most- applicable information. To be eligible for dose-response analysis, the studies had to further provide quantitative measure of dietary nitrate/nitrite intake for at least three categories with the estimates of RRs, corresponding 95%CI, category-specific or total number of cases and category-specific or total number of either person-years or non-cases.

supplementation [62–66]. The reason for this discrepancy is not clear. However, all of these results were in response to a very different phy- siological stimulus to the intervention presented here. Our subjects were exposed to hypobaric hypoxia gradually over a number of days; in chamber studies subjects tend to experience a much shorter duration and more rapidly induced period of normobaric hypoxia. For example, in one normobaric chamber study reporting an increase in cycling performance after just one dose of nitrate, subjects were decompressed to 15% oxygen in just 5 min [64]. Equally, the physiological response to normobaric and hypobaric hypoxia may not be the same, as suggested by a recent systematic review [67]. Currently Xtreme Alps remains the largest field study to date to explore the effects of dietary nitrate by taking serial measurements over a prolonged duration of hypobaric hypoxic exposure at high altitude.

Abstract Exposure to altitude results in multiple physio- logical consequences. These include, but are not limited to, a reduced maximal oxygen consumption, drop in arterial oxygen saturation, and increase in muscle metabolic per- turbations at a fixed sub-maximal work rate. Exercise capacity during fixed work rate or incremental exercise and time-trial performance are also impaired at altitude relative to sea level. Recently, dietary nitrate (NO 3 - ) supplemen-

The potential role of nitrite as an antimicrobial substance in the stomach may be of some importance in the ecology of the gastrointestinal tract and in host physiology. It has been shown that nitrite, under the acidic conditions of the stomach, may kill gut pathogens like Salmonella enteritidis, Escherichia coli, Salmonella typhimurium, and Yersinia enterocolitica, whereas acid alone has only a bacteriostatic effect. An in vivo study was conducted in order to assess the effects of dietary nitrate on microbiota and on the health of the gut (particularly in the stomach and small intestine). 96 weaning pigs were fed a diet containing high nitrate levels (15 mg and 150 mg) and then challenged with Salmonella enterica serovar typhimurium.

16 22 Ferguson SK, Hirai DM, Copp SW, et al. Impact of dietary nitrate supplementation via beetroot juice on exercising muscle vascular control in rats. J Physiol 2013; 591(Pt 2):547-557. 23 Muggeridge DJ, Sculthorpe N, Grace FM, et al. Acute whole body uva irradiation combined with nitrate ingestion enhances time trial performance in trained cyclists. Nitric Oxide 2015; 48:3-9.

Native highlanders (e.g. Sherpa) demonstrate remarkable hypoxic tolerance, possibly secondary to higher levels of circulating nitric oxide (NO) and increased microcirculatory blood flow. As part of the Xtreme Alps study (a randomised placebo-controlled trial of dietary nitrate supplementation under field conditions of hypobaric hypoxia), we investigated whether dietary supplementation with nitrate could improve NO availability and microvascular blood flow in lowlanders. Plasma measurements of nitrate, nitrite and nitroso species were per- formed together with measurements of sublingual (sidestream dark-field camera) and forearm blood flow (ve- nous occlusion plethysmography) in 28 healthy adult volunteers resident at 4559 m for 1 week; half receiving a beetroot-based high-nitrate supplement and half receiving an identically-tasting low nitrate ‘placebo’. Dietary supplementation increased plasma nitrate concentrations 4-fold compared to the placebo group, both at sea level (SL; 19.2 vs 76.9 μM) and at day 5 (D5) of high altitude (22.9 vs 84.3 μM, p < 0.001). Dietary nitrate sup- plementation also significantly increased both plasma nitrite (0.78 vs. 0.86 μM SL, 0.31 vs. 0.41 μM D5, p = 0.03) and total nitroso product (11.3 vs. 19.7 nM SL, 9.7 vs. 12.3 nM D5, p < 0.001) levels both at sea level and at 4559 m. However, plasma nitrite concentrations were more than 50% lower at 4559 m compared to sea level in both treatment groups. Despite these significant changes, dietary nitrate supplementation had no effect

During the study period, participants were instructed to follow their normal dietary habits, but were provided with a list of foods high in dietary nitrate and asked to abstain from these foods throughout the duration of the study. Prior to the study, participants filled out a 72 h food log (2 weekdays, 1 weekend day). A second 72 h food log was filled out at the end of the entire study to track any dietary changes. A copy of pre-testing food logs was given back to participants to facilitate the repli- cation of dietary intake patterns each day preceding test- ing. The participants were asked to avoid strenuous exercise, alcohol, and caffeine 24 h prior to each testing session. Furthermore, participants were requested to ab- stain from using antibacterial mouthwash and chewing gum as these are known to negatively impact production of nitric oxide [13]. Participants were also asked to arrive at each testing session adequately hydrated (i.e. without subjective feelings of thirst). Participants were allowed to use exercise aids (excluding chalk) such as tape or wrist wraps for the CrossFit specific “Grace” test, but had to

It is possible that nitrate supplementation is especially effective when conducting high- intensity exercise in a hypoxic environment, such that individuals across a range of aerobic fitness levels may derive a similar performance enhancing benefit from dietary nitrate supplementation. This has considerable relevance, given the widespread popularity of travel to high-altitude (i.e. hypobaric hypoxia) each year for recreational (e.g. hiking, skiing, mountaineering) and sporting (e.g. training camps, high-altitude running events, and cycle mountain stages) purposes in individuals with a range of different fitness levels. Therefore, the purpose of this study was to assess the effect of nitrate supplementation on physiological functioning and TT performance in moderate normobaric hypoxia (equivalent to 2500 m) in individuals with varying aerobic fitness levels (VO 2max ). We hypothesised that: (1) dietary

At the time of this review preparation, only seven studies examined the effects of long-term dietary nitrate supplementation on physiological responses and exercise performance in athletes. Three studies demonstrated an improved performance and four studies reported no effect of repeated beetroot supplementation of dietary nitrate (3-8d). The first two studies, performed in well trained athletes, showed that a 6-day beetroot ingestion (5.5 to 8 mmol of nitrate) improved the10-km cycling (55) and the 6 × 500 rowing (56) performance by 1.2% and 0.4% (by 1.7% in 4-6 reps), respectively. Finally, a recent study in master swimmers showed that beetroot juice (5.5 mmol of nitrate) consumed for 6 days, significantly increased the workload (by 6%) and reduced the energy cost (by 11%) at exercise intensity corresponding to the anaerobic threshold (57). Three points, however, should be considered before drawing conclusions from the above studies on the ergogenic value of long-term dietary nitrate supplementation in elite athletes. First, the within subject day-to-day variability in time trial performance was 1.0% that is very close to the reported effect of beetroot (55). Second, the worthwhile difference, index of practical significance, is very small for elite athletes (about 0.3% for rowers) (58). Third, the participants in Pinna’s et al. study were master athletes with VO 2 max

has a profound negative effect on physiological function and exercise performance (Bärtsch and Saltin, 2008). Arterial oxygen saturation declines (Calbet and Lundby, 2009), muscle metabolism is perturbed (Richardson et al., 2006; Vanhatalo et al., 2011), and maximal oxygen consumption ( VO ˙ 2max ) is decreased (Wehrlin and Hallén, 2006; MacInnis et al., 2015). Accordingly, exercise time to exhaustion (TTE) is reduced, and time-trial (TT) performance is slower at altitude compared with sea-level (Fulco et al., 1998). Interventions which help attenuate the decline in physiological functioning and exercise performance at altitude are therefore highly desirable. One strategy which has attracted considerable recent attention in this regard is dietary nitrate (NO − 3 ) supplementation.

Dietary nitrate supplementation has been shown to exert a variety of effects on physiological function, with recent evidence that short-term supplementation lowers the resting blood pressure [28] [29] [30], reduces the energetic cost of ex- ercise [28] [30] [31], activates muscle contraction [20] [32] [33], and enhances endurance [17] [34] and intense intermittent exercise performance [35]. How- ever, to the best of our knowledge, there is no sufficient evidence regarding the effects of nitrate ingestion before ECC on muscle contractile properties. The fol- lowing remarkable results were noted in this study. First, 6-day dietary nitrate supplementation, but not 3-day supplementation, mitigated ECC induced de- creases in force production, demonstrating that 6-day dietary nitrate supple- mentation prior to the ECC protocol markedly improved force production in rat fast-twitch muscles following ECC.

Initially, five participants ingested 210 mL (12.6 mmol) of dietary nitrate (Beet It Sport Shot, James White Drinks, Suffolk, UK) and our preliminary analysis revealed a modest increase (~12–15%) in exercising FBF 2 h after consumption. Previous studies in animals reported ~40% increase in hind limb blood flow during treadmill exercise in rats (Ferguson et al. 2013), so in an effort to ensure participants had an optimal dose for us to observe any change in FBF, we increased the dose (280 mL/16.8 mmol) and the duration (3 h) that we waited (Wylie et al. 2013a) prior to starting the BR trial in the subsequent participants (n = 6). Seven additional subjects underwent the same experimental protocol but ingested placebo shots (210 or 280 mL) free of dietary nitrate (James White Drinks) and served as a time control group. Both BR and placebo subjects were blinded to which shots they received.

The intervention was a custom formulated all-natural beetroot/fruit juice blend (produced and generously provided by Aurapa GmbH, Bietigheim-Bissingen, Germany), high in nitrate. The total daily nitrate dose targeted by this interven- tion was on the same order of magnitude (range 0.10 – 0.18 mmol/kg/day) as that shown by others to be effective in improving exercise performance at sea level [15,16] and divided into three individual doses for consumption in the morning, at midday and in the evening. The placebo juice was not entirely nitrate-free but contained a significantly ( N 90%) reduced content, which was achieved by using a beetroot juice in which nitrate was removed using a proprietary selective microbial denitrification method. Administration, at both sea level and high altitude, commenced 72 h prior to testing and continued throughout the study period. In order to account for dietary nitrate intake during the study period, meals were standardised in order to reduce excessive nitrate content. Also, a sample of each course was collected, blended and stored at − 40 °C for later nitrate content analysis. 2.7. Study setting

Effect of dietary nitrate supplementation on conduit artery blood flow, muscle 11. oxygenation, and metabolic rate during handgrip exercise 2.[r]

Abstract Introduction: The purpose of the present study was to assess the effects of acute nitrate NO3-rich beetroot juice supplementation on peripheral oxygen saturation SpO2, heart rat[r]

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Figure S1: Study design (upper panel) and protocol of standardised exercise test (lower panel). After an initial screening participants were randomised to either placebo or nitrate- rich beetroot juice in cross-over fashion for one week. After a one-week wash out period, participants were invited to return to the research centre and crossed to the other intervention. Measurements were conducted at baseline and end of each intervention giving a total of four measurement sessions. Detailed measurements of physical performance were performed at the research centre while when at home physical activity was monitored by triaxial

545 Table 3: Measures of free living physical activity after supplementation with either nitrate-rich or nitrate-depleted placebo beetroot juice measured over each one-week intervention [r]

34. Mirmiran P, Esfahani FH, Mehrabi Y et al (2010). Reliability and relative validity of an FFQ for nutrients in the Tehran lipid and glucose study. Public Health Nutr, 13(5):654-62. 35. García-Robledo E, Corzo A, Papaspyrou S (2014). A fast and direct spectrophotometric method for the sequential determination of nitrate and nitrite at low concentrations in small volumes. Mar Chem, 162:30-6.