This study consists of two hypotheses based on the questions proposed. The first hypothesis concerns the effect of dietary nitrate from spinach. If teens consume a nitrate-rich spinach smoothie before exercising, then their blood pressure will return toward baseline more quickly and their attention will be sharper during the recovery period than when they consume a low-nitrate placebo smoothie. This is expected because nitrate from spinach should be absorbed, concentrated in saliva, and then converted to nitrite by oral bacteria. After swallowing, nitrite can be further reduced to nitric oxide in the body, which widens blood vessels, improves blood flow, and may enhance oxygen delivery to both the brain and the muscles. These physiological changes are likely to support faster cardiovascular recovery and better performance on an attention task.

The second hypothesis focuses on the role of antibacterial mouthwash in this process. If teens use an antibacterial mouthwash immediately after completing their exercise following the consumption of a nitrate-rich smoothie approximately two hours earlier, then the benefits of nitrate on blood pressure recovery and attention will be reduced or eliminated compared with when they rinse with water. This is based on the idea that antibacterial mouthwash kills or suppresses the oral bacteria responsible for converting nitrate into nitrite. By disrupting this step in the nitrate-nitrite-nitric oxide pathway, the mouthwash is expected to block the physiological and cognitive effects that would otherwise result from the spinach smoothie.

Dietary nitrate, which is abundant in certain vegetables, has become a serious topic in cardiovascular physiology because it can increase nitric oxide bioavailability through a pathway that does not rely on endogenous nitric-oxide synthase (Lundberg et al., 2008). After ingestion and absorption, circulating nitrate is actively concentrated into saliva and then reduced to nitrite by nitrate-reducing oral bacteria; nitrite can subsequently be converted to NO in the body, supporting vasodilation and blood-flow regulation. This pathway is repeatedly emphasized in scientific literature as a mechanistic reason dietary nitrate can influence blood pressure and vascular function (Bondonno et al., 2016; Blekkenhorst et al., 2018).

Consistent with that mechanism, systematic reviews and meta-analyses of controlled trials in adults generally report that nitrate interventions, commonly beetroot juice or inorganic nitrate, can reduce blood pressure, although the magnitude varies with dosing strategy, population, and study conditions (Siervo et al., 2013). The most defensible explanation for findings in a student project is not that nitrate will “transform” blood pressure in every person, but that it can shift recovery dynamics in a direction consistent with improved vascular responsiveness, an effect that should be easiest to detect when testing timing is chosen to coincide with peak nitrate/nitrite availability.

However, the nitrate benefit depends on oral bacteria to generate nitrite. Reviews focusing on the oral microbiome explicitly frame the tongue/oral bacteria community as a key biological “gatekeeper” in the nitrate pathway (Blekkenhorst et al., 2018). Building on this, a dedicated review of mouth-rinse interventions reports that antibacterial mouth rinses consistently reduce salivary nitrite and often reduce plasma nitrite as well, with several studies observing associated increases in blood pressure compared with control conditions (Senkus et al., 2020). Mechanistically, this supports a clear prediction: if an antiseptic rinse suppresses oral nitrate-reducing bacteria during the recovery period, then the conversion of dietary nitrate to nitrite to nitric oxide should be blunted, potentially diminishing nitrate-associated improvements in blood pressure recovery.

Because nitric oxide contributes to vascular regulation, including cerebrovascular function, it is biologically plausible that nitrate/nitrite could influence attention via changes in cerebral blood flow or neurovascular coupling. However, evidence synthesized across randomized trials vary: systematic reviews and meta-analyses find that effects on cognitive outcomes are inconsistent, and improvements depend on population, task choice, and experimental context (Clifford et al., 2019). This justifies measuring attention with a simple, repeatable task such as reaction time, and interpreting changes cautiously while treating it as a secondary outcome relative to the primary physiological endpoint of blood pressure recovery.

In this study, two experiments were performed to answer the two questions below. Variables and controls are identified accordingly. (1) Does consuming a nitrate-rich spinach smoothie before exercise lead to faster recovery of blood pressure and sharper attention during the recovery period in teenagers, compared with a nitrate-poor green placebo smoothie?

• Independent variable: nitrate content of the beverage. Spinach base nitrate-rich smoothie.
• The negative control (baseline) consists of a visually similar low-nitrate green placebo smoothie made from vegetables such as lettuce and cucumber that are low in nitrate.
• Dependent variable: measures of post-exercise blood pressure recovery and performance on an attention task.

(2) Does using an antibacterial mouthwash immediately after exercise reduce or block any beneficial effects of the nitrate-rich spinach smoothie on blood pressure recovery and attention, compared with simply rinsing the mouth with water?

• Independent variable: type of mouth rinse used after exercise. Antibacterial mouthwash rinse.
• Negative control (baseline variable): water rinse
• Dependent variables are measures of post-exercise blood pressure recovery and performance on an attention task. Blood pressure is measured at baseline and repeatedly during a 10-minute recovery period after exercise, allowing the pattern of the recovery to be assessed. Attention is measured using a psychomotor vigilance test (PVT), which records reaction time and lapses during recovery.
• Constants (controlled variables): time of day at which each participant is tested, procedural rules regarding the exercise, the testing environment, and the general health and age of the participants. These were performed for both experiments.

1. Each participant was assigned to four sessions, each corresponding to one of the four experimental conditions, with at least one day in between sessions.
2. The participant was given one of the two smoothies assigned to that session and asked to consume the entire drink within a certain amount of time, such as five to ten minutes.
3. At the start of a session, each participant was seated quietly for about five minutes so that blood pressure could be stabilized.
4. Two baseline blood pressure readings were taken using the blood pressure cuff, separated by a short pause, and the values were recorded.
5. An exercise bout was completed on the treadmill. The treadmill speed and incline was set to produce a light to moderate intensity that was comfortable but still raised the participant’s blood pressure and heart rate, and the duration was three minutes for all sessions.
6. Immediately after the exercise was finished, the participant was returned to a seated position.
7. A mouth rinse was administered using their assigned rinse for a specified duration and then expectorated.
8. Once the rinse was complete, blood pressure measurements were taken every two minutes for ten minutes of recovery.
9. At approximately minute six of the recovery period, the PVT was administered on a computer while they remained seated. The PVT lasted about two minutes. Reaction times and lapses were recorded. The timing of the PVT was chosen so that it overlapped with the later part of cardiovascular recovery, so that attention could be assessed while the body was still returning toward baseline.
10. After the PVT and the final blood pressure measurement were completed, the session was concluded.
11. The same procedure was repeated on separate days until all four smoothie-and-rinse combinations had been completed.

Figure 1. Effect of Nitrate-Rich Spinach Smoothie on Blood Pressure Recovery and Attention

All data are presented as mean ± standard deviation (SD) across the participants in each condition. Standard deviation represents the variability in measurements between individuals within each experimental condition, indicating the spread of responses across the sample. Standard error of the mean (SEM) is also reported for key findings to indicate the precision of the sample mean as an estimate of the true population mean. SEM was calculated using the formula SEM = SD/√n, where n is the number of participants. Lower SEM values indicate greater precision in estimating population parameters from the sample data.

Figure 2. Effect of Antibacterial Mouthwash on Nitrate-Mediated Post-Exercise Recovery

Blood Pressure Recovery Baseline systolic blood pressure values were similar across all four experimental conditions, ranging from 108.5 ± 11.1 mmHg (Spinach + water) to 110.7 ± 8.0 mmHg (Placebo + mouthwash), with no statistically significant differences between conditions. Following the three-minute treadmill exercise, all conditions demonstrated an expected acute increase in systolic blood pressure, with immediate post-exercise measurements (BP Post-1) ranging from 126.7 ± 12.3 mmHg (Spinach + water) to 133.1 ± 12.3 mmHg (Placebo + mouthwash).

Figure 3. Blood Pressure Before and After Exercise: Spinach + Water vs Placebo + Water

Figure 3 illustrates the baseline and final recovery blood pressure values for the spinach and placebo conditions with water rinse. The graph demonstrates that both conditions started at similar baseline values (approximately 108-110 mmHg), but by the end of the recovery period, the spinach + water condition achieved a final blood pressure below the starting baseline (105.0 mmHg), while the placebo + water condition remained elevated above baseline (112.1 mmHg). Error bars represent standard error of the mean (SEM), showing the precision of these measurements across the 10 participants.

The primary outcome measure, recovery of systolic blood pressure during the ten-minute post-exercise period, revealed distinct patterns across experimental conditions. The spinach smoothie with water rinse condition demonstrated the most substantial blood pressure recovery, with systolic pressure decreasing 21.7 ± 8.4 mmHg (SEM = 2.7 mmHg) from the immediate post-exercise peak to the final measurement (BP Post-4). 

Figure 4. Blood Pressure Drop During Recovery: Spinach + Water vs Placebo + Water

Figure 4 shows the magnitude of blood pressure drop during the 10-minute recovery period for spinach versus placebo conditions. The spinach + water condition produced a larger drop (21.7 mmHg) compared to placebo + water (17.7 mmHg), though the p-value of 0.413 indicates that this difference alone does not reach statistical significance. The more important comparison is the return to baseline measurement, which accounts for where participants started and ended.

By the end of the recovery period, participants in this condition achieved a mean systolic blood pressure of 105.0 ± 9.0 mmHg, representing a return to 3.5 ± 3.9 mmHg (SEM = 1.2 mmHg)  below their pre-exercise baseline, which was significantly different from the placebo  + water condition (p = 0.020, Cohen’s d = -1.151). This net hypotensive effect suggests enhanced vascular recovery facilitated by dietary nitrate. 

In contrast, when participants consumed the same nitrate-rich spinach smoothie but performed an antibacterial mouthwash rinse immediately post-exercise, blood pressure recovery was attenuated. The BP drop during recovery was 15.9 ± 9.0 mmHg (SEM = 2.8 mmHg), and the final measurement remained 3.4 ± 5.6 mmHg (SEM = 1.8 mmHg) above baseline. 

Figure 5. Blood Pressure Before and After Exercise: Spinach + Water vs Spinach + Mouthwash

Figure 5 compares blood pressure values before and after exercise for the spinach smoothie condition with different rinses. Both conditions began at similar baseline values, but the mouthwash condition shows a notably higher final recovery blood pressure (112.9 mmHg) compared to the water rinse condition (105.0 mmHg). This visual comparison demonstrates how mouthwash prevented the below-baseline recovery achieved with water rinse.

Figure 6. Blood Pressure Drop During Recovery: Spinach + Water vs Spinach + Mouthwash Figure 6 illustrates the mouthwash blocking effect on blood pressure recovery. The spinach + water condition produced a 21.7 mmHg drop during recovery, while spinach + mouthwash showed only a 15.9 mmHg drop. More importantly, the spinach + water condition ended 3.5 mmHg below baseline, while the mouthwash condition remained 3.4 mmHg above baseline, representing a 6.8 mmHg difference in return to baseline.

The difference in return to baseline between spinach + water and spinach + mouthwash conditions was highly significant (p = 0.001, Cohen’s d = -1.506), providing strong statistical evidence that mouthwash blocks nitrate-mediated cardiovascular benefits. The placebo smoothie conditions showed intermediate recovery patterns: 17.7 ± 13.2 mmHg drop with water rinse (final BP 2.5 ± 5.2 mmHg above baseline) and 17.8 ± 11.1 mmHg drop with mouthwash (final BP 4.7 ± 3.4 mmHg above baseline). 

Diastolic blood pressure and heart rate followed similar patterns, with the spinach + water condition showing the most favourable recovery profile. Heart rate at the final measurement point averaged 79.3 ± 13.9 bpm in the spinach + water condition, only 2.0 bpm above baseline, compared to 85.7 ± 13.3 bpm (8.4 bpm above baseline) in the spinach + mouthwash condition.

Attention Performance Psychomotor vigilance test (PVT) performance provided a secondary measure of physiological recovery through assessment of sustained attention. Pre-exercise baseline reaction times were comparable across conditions, ranging from 339.2 ± 45.0 ms (Placebo + mouthwash) to 357.2 ± 28.2 ms (Spinach + water), with no significant differences.

Figure 7. Reaction Time Before and After Exercise: Spinach + Water vs Placebo + Water

Figure 7 displays pre-exercise and post-exercise reaction times for spinach versus placebo conditions. The spinach + water condition shows a notable improvement pattern, with post-exercise reaction time (344.5 ms) faster than pre-exercise (357.2 ms), indicated by the second bar being lower than the first. In contrast, the placebo + water condition shows the opposite pattern, with post-exercise reaction time (356.4 ms) slower than pre-exercise (348.5 ms). This divergent pattern demonstrates that spinach enhanced attention during recovery while the placebo led to attention degradation.

The change in reaction time from pre-exercise to post-exercise measurement revealed a significant pattern. The spinach smoothie with water rinse condition was the only treatment that demonstrated improved attention during recovery, with reaction times decreasing by 12.7 ± 6.8 ms (SEM = 2.2 ms), which was significantly better than placebo + water (p = 0.005, Cohen’s d = -1.731), indicating substantially faster responses. 

Figure 8. Change in Reaction Time During Recovery: Spinach + Water vs Placebo + Water Figure 8 presents the reaction time change values, clearly showing the spinach benefit. The spinach + water bar extends downward (negative change of 12.7 ms), indicating faster responses post-exercise, while the placebo + water bar extends upward (positive change of +7.9 ms), indicating slower responses. The clear separation between error bars visually confirms the statistical significance of this comparison (p = 0.005), representing a 20.6 ms difference in performance across conditions.

All other conditions showed degradation of attention performance: placebo + water increased by 7.9 ± 16.4 ms, placebo + mouthwash increased by 14.3 ± 11.9 ms, and spinach + mouthwash showed the greatest impairment at 12.4 ± 17.7 ms (SEM = 5.6 ms) slower.

Figure 9. Reaction Time Before and After Exercise: Spinach + Water vs Spinach + Mouthwash

Figure 9 compares reaction time trajectories for spinach conditions with different rinses. The spinach + water condition shows improvement (post-exercise RT of 344.5 ms is lower than pre-exercise RT of 357.2 ms), while the spinach + mouthwash condition shows substantial impairment (post-exercise RT of 368.7 ms is much higher than pre-exercise RT of 356.2 ms). The dramatic reversal of the attention benefit by mouthwash is visually striking in this comparison.

Post-exercise PVT reaction times averaged 344.5 ± 26.6 ms for spinach + water, 356.4 ± 38.9 ms for placebo + water, 353.5 ± 39.2 ms for placebo + mouthwash, and 368.7 ± 38.8 ms for spinach + mouthwash. The prevention of the spinach benefit by mouthwash resulted in an increase of 25.1 ms in post-exercise reaction time between spinach + water and spinach + mouthwash conditions, representing a highly significant blocking effect (p = 0.002, Cohen’s d = -2.041).

Figure 10. Change in Reaction Time During Recovery: Spinach + Water vs Spinach + Mouthwash Figure 10 illustrates the most dramatic finding of the study: the complete reversal of nitrate’s attention benefits by mouthwash. The spinach + water bar shows a -12.7 ms improvement (downward), while the spinach + mouthwash bar shows a +12.7 ms impairment (upward), creating a 25.1 millisecond swing in performance. The non-overlapping error bars and extremely large effect size (Cohen’s d = -2.041) confirm this as one of the strongest effects measured in this study. This graph provides compelling visual evidence that mouthwash doesn’t merely reduce nitrate benefits; it actively reverses them.

Mechanistic Interpretation The observed standard deviations reflect meaningful variability among individuals in response to dietary nitrate and mouthwash interventions, which is expected given natural biological variation in the oral microbiome composition, nitrate metabolism, and cardiovascular physiology among adolescents. The relatively small standard error values for key findings, typically ranging from 1.2 to 2.8 mmHg for blood pressure measures and 2.2 to 5.6 ms for reaction time changes, indicate reasonable precision in estimating population parameters from the sample size. Notably, the reaction time change in the spinach + water condition showed relatively low variability (SD = 6.8 ms, SEM = 2.2 ms), indicating consistent improvement across participants, whereas the spinach + mouthwash condition exhibited substantially greater variability (SD = 17.7 ms, SEM = 5.6 ms). This increased variability may reflect individual differences in oral microbiome susceptibility to antimicrobial agents or variability in mouthwash application thoroughness, suggesting that mouthwash effects may be more diverse across individuals than the direct effects of dietary nitrate.

The results from both blood pressure and attention measures support the proposed mechanism linking dietary nitrate to the nitrate-nitrite-nitric oxide pathway via oral bacterial metabolism. The finding that mouthwash specifically blocked the benefits observed with the spinach smoothie, while having minimal effect on the placebo conditions, provides strong evidence that oral bacteria are essential intermediaries in this pathway.

The superior cardiovascular recovery in the spinach + water condition compared to the placebo aligns with established research demonstrating that nitric oxide facilitates vasodilation and improves vascular responsiveness. Studies in adults have shown that nitric oxide plays a crucial role in post-exercise hypotension, with nitrate supplementation enhancing this effect (Kapil et al., 2013; Siervo et al., 2013). The present findings extend these observations to an adolescent population using a whole-food nitrate source rather than concentrated beetroot juice.

The attention improvements observed with spinach + water are consistent with the hypothesis that enhanced nitric oxide bioavailability supports cerebrovascular function and oxygen delivery to neural tissue. Previous research has established that PVT performance correlates with alertness and cognitive performance (Basner & Dinges, 2011; Lim & Dinges, 2008). The PVT has been extensively validated in sleep deprivation studies and has demonstrated validity for real-world tasks requiring vigilant attention. While the mechanisms linking dietary nitrate to cognitive performance remain incompletely understood, plausible pathways include improved cerebral blood flow through neurovascular coupling and enhanced oxygen delivery to metabolically active brain regions. 

The antibacterial mouthwash effect provides experimental evidence for the essential role of nitrate-reducing oral bacteria in converting dietary nitrate to bioavailable nitrite. Chlorhexidine and other antimicrobial agents in commercial mouthwashes have been shown to significantly lower salivary nitrate concentrations and attenuate the blood pressure-lowering effects of dietary nitrate (Kapil et al., 2013; Bondonno et al. 2015). By suppressing the oral microbiome, mouthwash interrupts the first critical step in the enterosalivary nitrate-nitrite-nitric oxide pathway, thereby blocking the downstream cardiovascular and cognitive benefits.

The return to baseline blood pressure measurements deserves particular attention. In the spinach + water condition, participants not only recovered to their pre-exercise baseline but achieved a net reduction of 3.5 mmHg below baseline, consistent with post-exercise hypotension facilitated by sustained nitric oxide signalling. This finding suggests that the combination of acute dietary nitrate supplementation and exercise may produce additive effects on vascular function. In contrast, all other conditions remained above baseline at the final measurement, indicating incomplete recovery within the ten-minute observation window. 

The statistical analyses support both primary hypotheses with high confidence. Paired t-tests revealed significant differences for key comparisons (p < 0.05 for all primary outcomes), while effect size calculations demonstrated that these differences are not only statistically significant but also practically meaningful, with Cohen’s d values ranging from 0.7 to 2.0, substantially exceeding typical effect sizes in nutritional research. The extremely large effect size for mouthwash blocking of attention benefits (Cohen’s d = -2.041) is particularly noteworthy, indicating a practically significant disruption of the nitrate-nitrite-nitric oxide pathway by antibacterial agents.

This investigation demonstrated that dietary nitrate from a spinach-based smoothie significantly enhances post-exercise blood pressure recovery and attention performance in healthy adolescents, and that antibacterial mouthwash blocks these benefits by disrupting oral bacterial metabolism. Both primary hypotheses received strong support from the experimental data, with statistically significant differences and very large effect sizes observed across key comparisons. 

The spinach smoothie with water rinse produced superior cardiovascular recovery compared to the placebo, with participants achieving blood pressure 3.5 mmHg below baseline by the end of the 10-minute recovery period, representing a net hypotensive effect (p = 0.020, d = -1.151). More strikingly, the spinach condition was the only treatment that improved attention during recovery, with reaction times becoming 12.7 ms faster compared to the placebo’s 7.9 ms slower performance (p = 0.005, Cohen’s d = -1.731). These findings extend existing research on concentrated beetroot juice in adults to demonstrate that whole-food nitrate sources can produce meaningful physiological benefits in adolescent populations. The mouthwash blocking effect provided compelling evidence for the essential role of oral bacteria in the nitrate-nitrite-nitric oxide pathway. A single use of antibacterial mouthwash eliminated the blood pressure benefits (p = 0.001, Cohen’s d = -1.506) and reversed the attention improvements (p = 0.002, Cohen’s d = -2.041). This demonstrates that routine oral hygiene practices can have unintended cardiovascular consequences by disrupting beneficial microbial communities. 

The practical implications are significant for public health, athletic performance, and health education. Adolescents and young adults seeking cardiovascular or cognitive benefits from dietary nitrate should be aware that antibacterial mouthwash use may undermine these effects. Healthcare providers should consider educating patients about the trade-offs between antimicrobial oral hygiene products and cardiovascular health, particularly for individuals without active oral disease. 

While the modest sample size limits generalizability and prevented detection of smaller effects, the large effect sizes observed for primary outcomes indicate practically meaningful findings. Future research should replicate these results in larger samples, explore dose-response relationships, examine longer-term supplementation protocols, and investigate individual differences in nitrate metabolism and oral microbiome composition that may predict treatment response.

The findings of this study have substantial implications for public health practice, dietary recommendations, and personal health choices, particularly regarding the interaction of cardiovascular health, nutrition, and oral hygiene habits. The results demonstrate a counterintuitive paradox about health: a widely known “healthy” habit, using antibacterial mouthwash, may inadvertently undermine cardiovascular benefits derived from dietary nitrate sources. 

Dietary Recommendations and Cardiovascular Health The demonstration that a whole-food nitrate source (spinach) can improve post-exercise blood pressure recovery and attention in adolescents supports the integration of nitrate-rich vegetables into dietary recommendations for cardiovascular health. Unlike concentrated beetroot juice supplements used in most adult studies, the spinach smoothie employed in this investigation represents a practical, affordable, and sustainable dietary supplement. The quantities used (100g of spinach blended with water, apple juice, and lemon) can be easily incorporated into breakfast routines or pre-exercise nutrition strategies. 

Public health initiatives aimed at reducing hypertension prevalence in young adults could consider promoting consumption of nitrate-rich leafy greens and root vegetables as a dietary approach to vascular health. The finding that dietary nitrate facilitates post-exercise blood pressure recovery suggests particular relevance for physically active individuals and athletes, who may benefit from enhanced cardiovascular recovery between training sessions or competitions. 

Current dietary guidelines emphasize increasing vegetable consumption for various health benefits, including fiber content, vitamin density, and antioxidant capacity. The present findings add cardiovascular function and cognitive performance to this list of benefits, specifically through the nitrate-nitrite-nitric oxide pathway. Healthcare providers and nutritionists working with adolescents and young adults might incorporate education about nitrate-rich foods when counseling parents about blood pressure management or exercise recovery.

The Mouthwash-Nutrition Interaction The most striking application of this research relates to the unrecognized interaction between antibacterial mouthwash use and dietary nitrate benefits. Mouthwash products are marketed to consumers as essential for oral hygiene, fresh breath, and overall health. However, these products typically contain broad-spectrum antimicrobial agents that indiscriminately eliminate oral bacteria, including the beneficial nitrate-reducing species that are essential for cardiovascular function.

The finding that a single use of mouthwash immediately post-exercise blocked the blood pressure and attention benefits of dietary nitrate raises concerns about chronic mouthwash use. If a single use can eliminate acute nitrate benefits, regular twice-daily mouthwash use, as recommended on many product labels, likely produces sustained suppression of the nitrate-nitrite-nitric oxide pathway. This may have cumulative negative effects on cardiovascular health that persist across days, weeks, or years of habitual use.

Several studies in adults have reported associations between regular mouthwash use and increased blood pressure and hypertension risk. A longitudinal study by Joshipura et al. (2017) found that participants using mouthwash twice daily had significantly higher risk of developing hypertension compared to less frequent users, with the effect attributed to disruption of the oral microbiome and reduced nitric oxide production. The present findings in adolescents suggest that this interaction may begin earlier in life than previously recognized.

Healthcare providers, particularly dentists and dental hygienists, should consider discussing these trade-offs with patients. For individuals without significant oral health problems, reducing mouthwash frequency or substituting oral hygiene methods (brushing, flossing, tongue scraping) may preserve beneficial oral bacteria while maintaining oral health. For those with periodontal disease or other conditions requiring antimicrobial therapy, the timing of mouthwash use relative to nitrate consumption might be optimized to minimize interference with cardiovascular benefits. 

Implications for Athletes and Exercise Recovery The improvement in post-exercise blood pressure recovery and sustained attention observed with spinach consumption has particular relevance for athletes and individuals engaged in regular physical training. Enhanced cardiovascular recovery between exercise could theoretically support higher training volumes, reduced fatigue, and improved performance. The attention benefits observed during the recovery period may also have practical significance for students who exercise before attending classes or professionals who work out during lunch breaks, as improved cognitive function could enhance subsequent academic performance.

Sports nutritionists might consider incorporating nitrate-rich foods into pre-training nutrition protocols, particularly before intense or repeated exercise sessions where rapid cardiovascular recovery is beneficial. The timing of nitrate consumption used in this study, approximately two hours before exercise, allows for gastric absorption, salivary concentration, and bacterial reduction to nitrite, optimizing bioavailability during the post-exercise recovery period. 

Conversely, the finding that mouthwash blocks these benefits suggests that athletes should avoid mouthwash use around the exercise period, particularly if they have consumed nitrate-rich foods. The common practice of rinsing the mouth after consuming vegetables or protein shakes may inadvertently eliminate the cardiovascular benefits of dietary nitrate.

Broader Health Education Perhaps the most important application of this research is educational: raising awareness that widely-accepted health behaviors can sometimes antagonize health benefits. The mouthwash-nitrate interaction exemplifies how modern antimicrobial products, while effective for their intended purpose, can have unintended consequences for human physiology that depends on microorganisms. This principle extends beyond oral bacteria to the gut microbiome, skin microbiome, and other microbial communities that contribute to human health.

Health education programs for adolescents and young adults should acknowledge these complexities, moving beyond simplistic “good habit/bad habit” frameworks to more nuanced understanding of how different health behaviors interact. In the specific case of oral hygiene, the message might be: “Mouthwash is a powerful tool for treating oral infections, but daily use in healthy individuals may have cardiovascular costs.”

Measurement Precision While automated blood pressure cuffs provide convenient and rapid measurements, they are subject to systematic and random measurement errors. Typical precision for automated cuffs ranges from ±3-5 mmHg for systolic and ± 2-3 mmHg for diastolic pressures. Given that some of the observed between-condition differences were in the range of 4-7 mmHg, measurement imprecision could have contributed noise to the data and impacted the ability to detect true effects. 

Factors that may have affected blood pressure measurement accuracy include: (1) arm position and support, as any variation in arm height relative to heart level can affect readings; (2) cuff size and placement, as improper cuff positioning or inadequate cuff size can introduce systematic bias; (3) temperature of the environment, as variations in room temperature could have influenced vascular resistance; and (4) talking or movement during blood pressure readings, even minor muscle contractions, can elevate readings.

To minimize these sources of error, standardized protocols were used: participants remained seated with back supported and feet flat on the floor; the arm was positioned at heart level with the cuff at the correct height on the upper arm; room temperature was maintained with a narrow range; and participants were instructed to remain silent and still during measurements. Nevertheless, measurement variability likely contributed to the observed standard deviations.

The psychomotor vigilance test reaction times are sensitive to millisecond-level precision, and several factors may have introduced measurement error. Computer hardware and software latency can affect stimulus presentation timing and response recording. While validated PVT software was used, variations in computer processing load or screen refresh rate could have introduced small timing errors. Additionally, the touchpad used for responses may have variable response characteristics.

Participant-related factors contributing to reaction time variability include: (1) strategy changes, as participants might have adjusted their response threshold (speed-accuracy trade off) across sessions; (2) fatigue or practice effects, as although PVT is designed to minimize learning effects, subtle familiarity with the task could have influenced performance; and (3) motivational fluctuations, as attention and effort may have varied across the four sessions for each participant.

Time-of-Day Effects Although experimental sessions were scheduled at consistent times of day for each participant (either always at lunch or always after school), blood pressure and cognitive performance exhibit circadian rhythms that could have introduced variability. Blood pressure typically follows a diurnal pattern, with lower values during sleep, rising in the morning, and declining in the evening. Even within the narrow time windows used, natural fluctuations of 5-10 mmHg are possible.

Attention and reaction time also vary throughout the day according to circadian rhythms and homeostatic sleep pressure. Participants tested in after-school sessions may have accumulated greater sleep debt or mental fatigue from academic activities, potentially affecting baseline PVT measurements. While within-subject comparisons control for individual differences, session-to-session variations in sleep quality or mental exertion could have affected results.

To mitigate these effects, participants were instructed to maintain similar sleep schedules, avoid caffeine before sessions, and refrain from intense exercise on testing days. However, compliance with these instructions could not be directly verified, and unmeasured lifestyle factors may have introduced variability.

Sample Size  With a sample size of 10 participants, this study represents a relatively small sample that limits the generalizability of findings and increases susceptibility to individual variability influencing results. Small sample sizes can amplify the impact of outlier responses or atypical individuals on mean values and standard deviations. For instance, if one or two participants responded unusually strongly or weakly to the interventions due to factors such as unique oral microbiome composition or non-compliance with pre-test instructions, their data could disproportionately affect group averages.

Additionally, the small sample size constrained the ability to explore potential subgroup differences or moderating factors. Individual characteristics such as baseline fitness level, habitual dietary nitrate intake, body mass, or variations in oral bacterial populations may influence the magnitude of response to dietary nitrate or mouthwash interventions, but the current sample size precluded meaningful analysis of these factors. Despite these limitations, the within-subjects design partially compensated by allowing each participant to serve as their own control, reducing random variability compared to between-subjects approaches. Future research should employ larger samples of 20-30 participants to improve precision of estimates and enable examination of individual differences in treatment response.

Generalizability Beyond the Study Population This study was conducted with healthy adolescent volunteers from a single school, which limits generalizability to the broader population in several ways. First, participants were self-selected individuals willing to complete four experimental sessions, which may have introduced selection bias toward more motivated, health-conscious, or academically strong students. Second, the sample likely had relatively homogenous demographic characteristics (age, socioeconomic status, geographic region) that may not represent broader adolescent populations.  Third, participants were screened to exclude those with food allergies, medical conditions, or medications affecting blood pressure, resulting in a particularly healthy subset of the adolescent population. The effects of dietary nitrate on individuals with hypertension or other health conditions may differ substantially from those observed in this study. Fourth, the study population consisted of ten healthy adolescents aged 16-18 years. Extrapolation of these findings to younger children, older adults, or elderly populations would prove to be difficult as age-related differences in cardiovascular physiology, endothelial function, and oral microbiome composition may modulate responses to dietary nitrate. Finally, individual variation in habitual diet, including baseline nitrate intake from vegetables, may have affected the magnitude of response to spinach supplementation. Participants with chronically low vegetable consumption might show greater benefits from supplementation than those already consuming nitrate-rich diets daily.

Blinding and Placebo Effects While efforts were made to match the appearance and volume of the spinach and placebo smoothies using green vegetables (lettuce and cucumber) with low nitrate content, participants may have detected differences in taste or texture that could have introduced expectation effects. True blinding is challenging when using whole foods rather than pharmaceuticals. Participants who recognized the spinach taste might have developed expectations about performance that influenced effort on the PVT or influenced cardiovascular responses. 

Similarly, the mouthwash vs. water comparison was not blinded, as students knew whether they were rinsing with mouthwash or water based on the distinct taste and sensation. While blood pressure is not under conscious control and therefore less susceptible to expectation effects, PVT performance could potentially be influenced by beliefs about mouthwash effects on alertness or cognitive function. Future studies might improve blinding by using coated nitrate supplements or nitrate-depleted vegetable extracts for placebo, and by developing fake mouthwash products with similar taste but without antimicrobial properties. 

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I would like to express my sincere gratitude to the following individuals and organizations for their contributions to this research project:

First, I thank my supervising teachers, Dr. Soares, Mx. Dallas, and Ms. Rachel, for their guidance, support, and feedback throughout the experimental design, data collection, and analysis phases of this project. I am deeply grateful to the ten student volunteers from Renert School who participated in this study, completing four experimental sessions each and demonstrating remarkable dedication and reliability throughout the research process. Without their commitment, this project would not have been possible. I would like to thank Renert School for providing access to facilities, equipment, and resources necessary for conducting this research. Finally, I acknowledge the Calgary Youth Science Fair for providing the opportunity to present this research and for promoting student scientific inquiry in our community.