Effect of Inorganic Nitrate on Exercise Capacity in Heart Failure With Preserved Ejection Fraction

The researchers tested whether a single dose of inorganic nitrate (12.9 mmol, delivered as concentrated beetroot juice) could improve exercise capacity in people with heart failure with preserved ejection fraction (HFpEF), compared to an identical-tasting placebo drink that had the nitrate removed.

Intervention: 140 mL of nitrate-rich beetroot juice (BEET IT Sport, containing 12.9 mmol of inorganic nitrate)

Comparator: 140 mL of identical nitrate-depleted placebo beetroot juice

Primary outcome: Exercise efficiency (total work performed divided by total oxygen consumed)

Secondary outcomes: Peak oxygen uptake (peak V̇O2), total work performed during exercise, vasodilatory reserve (change in systemic vascular resistance from rest to peak exercise), cardiac output response to exercise, arterial wave reflections (augmentation index), and skeletal muscle mitochondrial oxidative function

Sample size: 17 subjects completed the study (all analyses based on this number)

Population: Adults with symptomatic heart failure with preserved ejection fraction (HFpEF)

Key characteristics:

• Mean age: 65 ± 11 years
• 71% male (12 men, 5 women)
• All had preserved left ventricular ejection fraction (>50%)
• All had evidence of elevated filling pressures (E/e' ratio >8 plus at least one other sign)
• Mean body mass index: 33.5 ± 6.9 kg/m² (obese range)
• 53% had hypertension, 41% had diabetes, 41% had coronary artery disease
• All on stable medical therapy

Setting: Single academic medical center (Hospital of the University of Pennsylvania and Philadelphia Veterans Affairs Medical Center)

Exclusion criteria: Noncardiac conditions limiting exercise (orthopedic issues, peripheral artery disease, neuromuscular disorders), gait instability, nonsinus rhythm, significant valvular disease, significant lung disease, recent acute coronary syndrome or revascularization (within 60 days), or any condition compromising safe exercise

Plasma nitrate/nitrite levels: Blood samples taken 2 hours after drink ingestion, centrifuged, and stored at -80°C for later batch analysis

Peak oxygen uptake (peak V̇O2): Measured via breath-by-breath expired gas analysis using a Parvo Medics True One 2400 metabolic cart during maximal-effort supine cycle ergometry. Peak V̇O2 was averaged over the final 30 seconds of exercise.

Total work performed: Calculated from the graded exercise protocol (starting at 12.5 W for 3 minutes, increasing to 25 W for 3 minutes, then increasing by 25 W every 3 minutes thereafter until exhaustion)

Exercise efficiency: Ratio of total work performed (in kJ) to total oxygen consumed (in L O2)

Cardiac output: Calculated from left ventricular outflow tract (LVOT) Doppler velocity-time integral measured via echocardiography at rest and immediately at peak exercise cessation

Systemic vascular resistance: Calculated as mean arterial pressure divided by cardiac output, measured at rest and peak exercise

Arterial wave reflections (augmentation index): Measured via radial arterial tonometry using a high-fidelity Millar tonometer, expressed as a percentage (lower = better, less wave reflection)

Skeletal muscle mitochondrial oxidative function: Assessed via near-infrared spectroscopy (NIRS) during a forearm exercise protocol (not fully detailed in abstract but mentioned in methods)

Blood pressure: Measured with a validated oscillometric device (Omron HEM-705CP) every 10 minutes for 2 hours after drink ingestion

NT-pro-BNP: Measured from stored blood samples using Orthoclinical Diagnostic Vitros 3600 (upper limit of normal: 124 pg/mL)

Study design: Randomized, double-blind, placebo-controlled crossover trial

Randomisation: Subjects were randomly assigned to receive either nitrate-rich beetroot juice or placebo first, then crossed over to the other arm after a washout period.

Blinding: Both the investigators and subjects were blinded to treatment assignment. The placebo drink was identical in appearance and taste but had the nitrate removed. All data quantification (cardiopulmonary exercise testing, echocardiography) was performed by investigators blinded to treatment condition.

Washout period: At least 5 days between treatment arms (mean: 11.8 days, range: 5–42 days)

Duration: Single-dose study – subjects consumed the drink 3 hours before exercise testing. Each subject completed two testing sessions (one per arm) separated by the washout period.

Timing of measurements: Blood pressure was measured every 10 minutes for 2 hours post-drink. Blood draw occurred at 2 hours post-drink. Exercise testing began at 3 hours post-drink.

Statistical approach: Paired comparisons between nitrate and placebo conditions (crossover design). Data presented as mean ± standard deviation or median with interquartile ranges. P-values reported for primary and secondary outcomes.

What this design can and cannot prove:

Can prove:

• Causal effect of a single dose of inorganic nitrate on exercise performance within individuals (crossover design controls for between-person variability)
• Acute physiological mechanisms (vasodilation, cardiac output, arterial stiffness) within the 3-hour window post-ingestion

Cannot prove:

• Long-term effects of chronic nitrate supplementation (single-dose study only)
• Whether effects persist, diminish, or increase with repeated dosing
• Whether effects translate to real-world functional improvements (e.g., walking distance, quality of life)
• Whether effects are clinically meaningful for hard outcomes (hospitalization, mortality)
• Whether effects differ by sex, age, or comorbidities (small sample, limited subgroup analysis)

Major methodological strengths:

• Double-blind, placebo-controlled design eliminates placebo effect and observer bias
• Crossover design reduces between-subject variability (each person serves as their own control)
• Blinded data quantification reduces measurement bias
• Validated, objective outcome measures (not self-report)

Major methodological weaknesses:

• Very small sample size (n=17) – limits generalizability and increases risk of false positives
• Single-dose design – cannot assess chronic effects or tolerance
• Single-center study – may not generalize to other populations or settings
• Short washout period (minimum 5 days) – possible carryover effects, though nitrate has short half-life
• No assessment of dietary nitrate intake control between sessions (subjects asked to avoid mouthwash but not standardized diet)
• Supine cycle ergometry – not representative of most daily activities (walking, stair climbing)
• No assessment of subjective exercise tolerance or symptoms (only objective measures)

Primary outcome – Exercise efficiency:

• No significant change: Nitrate vs. placebo (data not reported as significant in abstract; authors state "efficiency was unchanged")

Secondary outcomes – Exercise capacity:

• Peak V̇O2: 12.6 ± 3.7 vs. 11.6 ± 3.1 mL O2·min⁻¹·kg⁻¹ (nitrate vs. placebo); P = 0.005 (approximately 9% increase)
• Total work performed: 55.6 ± 35.3 vs. 49.2 ± 28.9 kJ; P = 0.04 (approximately 13% increase)

Vascular outcomes:

• Systemic vascular resistance reduction with exercise: −42.4 ± 16.6% vs. −31.8 ± 20.3% (nitrate vs. placebo); P = 0.03 (greater vasodilation with nitrate)
• Cardiac output increase with exercise: 121.2 ± 59.9% vs. 88.7 ± 53.3%; P = 0.006 (greater cardiac output reserve with nitrate)
• Aortic augmentation index (resting): 132.2 ± 16.7% vs. 141.4 ± 21.9%; P = 0.03 (lower wave reflections with nitrate, indicating less arterial stiffness)

Biochemical outcomes:

• Plasma nitrate metabolites: Median 326 vs. 10 μmol/L (nitrate vs. placebo); P = 0.0003 (massive increase confirming absorption)

Mitochondrial function:

• Tended to improve with nitrate but did not reach statistical significance (exact P-value not reported in abstract)

Blood pressure:

• Not explicitly reported as a primary outcome, but nitrate is known to lower blood pressure (data not shown in abstract)

Exercise capacity improvement: On average, people could exercise to a peak oxygen consumption about 1.0 mL O2·min⁻¹·kg⁻¹ higher after nitrate – roughly a 9% improvement. To put this in perspective, this is similar to the improvement seen with several months of supervised exercise training in heart failure patients.

Total work: People performed about 6.4 kJ more total work after nitrate – equivalent to approximately 1.5 minutes of additional cycling at 25 Watts, or about 150 extra meters walked on a flat surface.

Vasodilation: The blood vessels dilated about 33% more during exercise after nitrate (42% vs. 32% reduction in resistance), meaning the heart could pump blood more easily to working muscles.

Cardiac output: The heart's ability to increase output during exercise was about 37% greater after nitrate (121% vs. 89% increase from rest), meaning more oxygenated blood reached the muscles.

Arterial stiffness: The augmentation index dropped by about 9 percentage points (from 141% to 132%), indicating the heart faced less resistance from reflected pressure waves – a meaningful reduction comparable to some blood pressure medications.

Practical translation: For a person with HFpEF who can typically walk about 400 meters in 6 minutes, a 9-13% improvement might translate to walking an additional 35-50 meters before needing to stop – noticeable but not transformative.

What the authors acknowledge:

• Small sample size (n=17)
• Single-dose design – cannot assess chronic effects
• Supine cycle ergometry may not reflect upright daily activities
• No assessment of submaximal exercise endurance (only maximal effort)
• Potential for type II error (false negative) on some secondary outcomes due to small sample

Critical reader observations:

• Industry funding: The beetroot juice was provided by James White Drinks Ltd (manufacturer of BEET IT Sport), though the company had no role in study design or analysis
• No dietary standardization: Subjects were not placed on a low-nitrate diet before testing, so baseline nitrate intake varied and could have influenced results
• No assessment of oral microbiome: Nitrate-to-nitrite conversion depends on oral bacteria; subjects were asked to avoid mouthwash but oral flora was not characterized
• Short washout period: Minimum 5 days may be insufficient if there are any long-lasting effects on mitochondrial function or vascular remodeling
• No subjective measures: No assessment of perceived exertion (Borg scale), breathlessness, or quality of life – only objective lab measures
• Sex imbalance: 71% male – results may not generalize equally to women with HFpEF
• No placebo run-in: No assessment of whether subjects could distinguish active from placebo (though blinding appeared effective)
• Single time point: All measurements taken at 3 hours post-dose – effects may peak earlier or later in different individuals
• No assessment of adverse effects: Beetroot juice can cause beeturia (red urine) and gastrointestinal upset, but these were not systematically reported
• Population specificity: Results apply only to HFpEF patients with preserved ejection fraction >50% and elevated filling pressures – not generalizable to other forms of heart failure or healthy individuals

For someone running their own n=1 experiment:

What to test

• Intervention: Concentrated beetroot juice (or sodium nitrate supplement) providing approximately 12-13 mmol (about 800-900 mg) of inorganic nitrate
• Dose timing: Consume 2.5-3 hours before exercise (peak plasma nitrate occurs around 2-3 hours post-ingestion)
• Dose form: 140 mL of concentrated beetroot juice (e.g., BEET IT Sport, BeetElite, or homemade concentrated beetroot juice) or sodium nitrate capsules (available as supplements)
• Alternative: 300-500 mL of regular beetroot juice (lower concentration, may need larger volume)

Minimum meaningful duration

• Acute effect: Single dose can be tested in one session (3-hour protocol)
• Chronic effect: For sustained benefits, test daily supplementation for 7-14 days minimum (to assess tolerance, adaptation, and cumulative effects)
• Washout: At least 3-5 days between conditions (nitrate half-life is ~5-6 hours, but vascular effects may persist longer)

What to measure

• Primary metric: Exercise endurance or capacity (e.g., time to exhaustion on a fixed workload, distance walked in 6 minutes, or total work in kJ on a cycle ergometer)
• Secondary metrics:
  • Resting blood pressure (brachial cuff, seated, after 5 minutes rest)
  • Heart rate response to submaximal exercise (e.g., heart rate at a fixed workload)
  • Rating of perceived exertion (Borg scale 6-20) at a fixed time point during exercise
  • Oxygen saturation (pulse oximeter) during and after exercise
• Optional advanced metrics:
  • Pulse wave velocity or augmentation index (if you have access to a SphygmoCor or similar device)
  • Near-infrared spectroscopy (NIRS) for muscle oxygenation (if available)
  • Blood nitrate/nitrite levels (commercial lab testing)

Key confounds to control for

• Dietary nitrate intake: Standardize diet for 24-48 hours before each test (avoid beetroot, spinach, arugula, celery, lettuce, radishes, and cured meats)
• Oral hygiene: Do not use mouthwash or antibacterial toothpaste on test days (kills nitrate-reducing bacteria)
• Time of day: Test at the same time of day (circadian variation in vascular function)
• Pre-exercise meal: Standardize what and when you eat (avoid high-fat meals that impair vascular function)
• Hydration: Maintain consistent hydration status (dehydration affects blood volume and exercise capacity)
• Medications: Avoid phosphodiesterase-5 inhibitors (Viagra, Cialis) for 48 hours before testing (interaction with nitrate pathway)
• Caffeine: Standardize or avoid caffeine on test days (vasoactive)
• Exercise timing: Avoid strenuous exercise 24 hours before testing (residual fatigue and vascular effects)
• Menstrual cycle (for women): Test during the same phase of cycle (hormonal effects on vascular function)
• Temperature: Test in a temperature-controlled environment (heat affects vasodilation)

What a positive result would look like

• Exercise capacity: ≥8-10% improvement in time to exhaustion, distance walked, or total work performed (the study found ~9-13% improvement)
• Blood pressure: ≥3-5 mmHg reduction in resting systolic blood pressure (typical nitrate effect)
• Heart rate: Lower heart rate at a fixed submaximal workload (indicating improved cardiovascular efficiency)
• Perceived exertion: Borg scale rating 1-2 points lower at the same workload or time point
• Recovery: Faster return to resting heart rate after exercise (e.g., heart rate drops 10-15 bpm faster in first 2 minutes of recovery)

Example positive result: "After beetroot juice, I cycled 12.5 minutes at 50W before exhaustion, compared to 11.0 minutes after placebo – a 14% improvement. My heart rate at 5 minutes was 8 bpm lower, and my perceived exertion was 1 point lower on the Borg scale."

Caveat: If you don't see an effect, consider that nitrate responsiveness varies by individual (