The effect of dietary nitrate supplementation on the oxygen cost of cycling, walking performance and resting blood pressure in individuals with chronic obstructive pulmonary disease: A double blind placebo controlled, randomised control trial

Abstract

Background Chronic obstructive pulmonary disease (COPD) results in exercise intolerance. Dietary nitrate supplementation has been shown to lower blood pressure (BP), reduce the O2 cost of exercise, and enhance exercise tolerance in healthy volunteers. This study assessed the effects of dietary nitrate on the O2 cost of cycling, walking performance and BP in individuals with mild-moderate COPD. Methods Thirteen patients with mild-moderate COPD were recruited. Participants consumed 70 ml of either nitrate-rich (6.77 mmol nitrate; beetroot juice) or nitrate-depleted beetroot juice (0.002 mmol nitrate; placebo) twice a day for 2.5 days, with the final supplement ~3 hours before testing. BP was measured before completing two bouts of moderate-intensity cycling, where pulmonary gas exchange was measured throughout. The six-minute walk test (6MWT) was completed 30 minutes subsequent to the second cycling bout. Results Plasma nitrate concentration was significantly elevated following beetroot juice vs. placebo (placebo; 48 ± 86 vs. beetroot juice; 215 ± 84 µM, P=0.002). No significant differences were observed between placebo vs. beetroot juice for O2 cost of exercise (933 ± 323 vs. 939 ± 302 ml: min-1; P=0.88), distance covered in the 6MWT (456 ± 86 vs. 449 ± 79 m; P=0.37), systolic BP (123 ± 14 vs. 123 ± 14 mmHg; P=0.91), or diastolic BP (77 ± 9 vs. 79 ± 9 mmHg; P=0.27). Conclusion Despite a large rise in plasma nitrate concentration, two days of nitrate supplementation did not reduce the O2 cost of moderate intensity cycling, increase distance covered in the 6MWT, or lower BP.