Rationale: Dietary nitrate supplementation improves skeletal muscle oxygen utilisation and vascular endothelial function. We hypothesised that these effects might be sufficient to improve exercise performance in patients with COPD and hypoxia severe enough to require supplemental oxygen.

Methods: We conducted a single-centre, double-blind, placebo-controlled, cross-over study, enrolling adults with COPD who were established users of long-term oxygen therapy. Participants performed an endurance shuttle walk test, using their prescribed oxygen, 3 hours after consuming either 140 mL of nitrate-rich beetroot juice (BRJ) (12.9 mmol nitrate) or placebo (nitrate-depleted BRJ). Treatment order was allocated (1:1) by computer-generated block randomisation.

Measurements: The primary outcome was endurance shuttle walk test time. The secondary outcomes included area under the curve to isotime for fingertip oxygen saturation and heart rate parameters during the test, blood pressure, and endothelial function assessed using flow-mediated dilatation. Plasma nitrate and nitrite levels as well as FENO were also measured.

Main results: 20 participants were recruited and all completed the study. Nitrate-rich BRJ supplementation prolonged exercise endurance time in all participants as compared with placebo: median (IQR) 194.6 (147.5–411.7) s vs 159.1 (121.9–298.5) s, estimated treatment effect 62 (33–106) s (p<0.0001). Supplementation also improved endothelial function: NR-BRJ group +4.1% (−1.1% to 14.8%) vs placebo BRJ group −5.0% (−10.6% to –0.6%) (p=0.0003).

Conclusion: Acute dietary nitrate supplementation increases exercise endurance in patients with COPD who require supplemental oxygen.