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

Background and objective: Dietary beetroot juice (BR) supplementation has been shown to reduce the oxygen (O-2) 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 (2x70 mL twice daily, each containing 300 mg nitrate) or placebo (PL) (2x70 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), O-2 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, O-2 consumption during submaximal cycling, or physical activity level during the intervention period.