Dietary beetroot juice - effects on physical performance in COPD patients: a randomized controlled crossover trial

Abstract

Background and objective: Dietary beetroot juice (BR) supplementation has been shown to reduce the oxygen (O₂) consumption of standardized exercise and reduce resting blood pressure (BP) in healthy individuals. However, the physiological response of BR in chronic obstructive pulmonary disease (COPD) remains controversial. The objective was to test exercise performance in COPD, supplementing with higher doses of BR for a longer duration compared to previous trials in this patient group.

Methods: Fifteen COPD patients consumed concentrated BR (2×70 mL twice daily, each containing 300 mg nitrate) or placebo (PL) (2×70 mL twice daily, nitrate-negligible) in a randomized order for 6 consecutive days. On day 7, participants consumed either BR or PL 150 min before testing. BP was measured before completing 6-minute walk test (6MWT) and two trials of submaximal cycling. The protocol was repeated after a minimum washout of 7 days.

Results: Plasma nitrite concentration was higher in the BR condition compared to PL (P<0.01). There was no difference between the BR and PL conditions regarding the covered distance during the 6MWT (mean ± standard error of the mean: 515±35 m (BR) vs 520±38 m (PL), P=0.46), O₂ consumption of submaximal exercise (trial 1 P=0.31 vs trial 2 P=0.20), physical activity level (P>0.05), or systolic BP (P=0.80). However, diastolic BP (DBP) was reduced after BR ingestion compared to baseline (mean difference: 4.6, 95% CI: 0.1-9.1, P<0.05).

Conclusion: Seven days of BR ingestion increased plasma nitrite concentrations and lowered DBP in COPD patients. However, BR did not increase functional walking capacity, O₂ consumption during submaximal cycling, or physical activity level during the intervention period.

Keywords: beetroot juice; blood pressure; chronic obstructive pulmonary disease; exercise; nitrate; nitric oxide; nitrite.

Figure 1

Schematic overview of the study protocol (top) and the experimental protocol (bottom) completed during the habituation visit and at day 7 of each intervention period (indicated by dashed arrows). Note: *indicates the time when the measurements were performed. Abbreviations: BP, Blood Pressure; 6MWT, 6-minute walk test; BR, Beetroot juice; PL, Placebo; Borg-RPE, Borg scale for ratings of perceived exertion; NO₂⁻, Nitrite.

Figure 2

Flow of participants including enrollment, randomization, and completion.

Figure 3

Individual and mean plasma nitrite (nM) at the experimental day at arrival (0 min), 150 and 210 min after ingestion of either (A) placebo (PL) or (B) beetroot juice (BR). Nitrite was significantly higher in the BR period compared to PL (P<0.01), and nitrite increased after ingestion of BR, but not after PL (time P<0.01, interaction P<0.05). Note: *P<0.01, nitrite higher at 150 and 210 min after ingestion of BR compared to arrival (0 min).

Figure 4

Individual and mean distance covered in meters during 6MWT. Note: Data are presented as mean ± standard error of the mean (n=15). Abbreviation: 6MWT, 6-minute walk test.

Figure 5

Oxygen consumption during submaximal cycling (entire period). Notes: Data are presented as mean ± standard error of the mean (n=13). (A) Trial 1 (interaction P=0.31; time P<0.001) and (B) trial 2 after 10 min break (interaction P=0.20; time P<0.001). ***indicates a significant increase in oxygen consumption during the trial (P<0.001).

Figure 6

Individual and mean response in (A) systolic blood pressure (mmHg) and (B) diastolic blood pressure (mmHg) (n=15). Notes: *P<0.01 denotes difference between baseline and 150 min after ingestion of both placebo and BR. **P<0.05 denotes difference between baseline and 150 min after ingestion of BR. Abbreviations: BP, blood pressure; BR, beetroot juice.