Efficacy and safety of nitrate supplementation on exercise tolerance in chronic obstructive pulmonary disease: A systematic review and meta-analysis

BACKGROUND: Exercise intolerance was prevalent in people with chronic obstructive pulmonary disease (COPD) and had a detrimental effect on the quality of life. We aimed to evaluate the efficacy and safety of nitrate supplementation in exercise tolerance of people with COPD. METHODS: We searched medical databases including Cochrane Library, EMBASE, and PubMed from inception to October 2020 for randomized control trials in treating COPD with nitrate supplementation. RESULTS: Nine trials were identified. Compared with placebo, nitrate supplementation has no significant effect on the following variables: exercise endurance time (standard mean difference [SMD]: 0.06; 95% confidence interval [CI]: –0.39 to 0.52; P = .79), exercise capacity (SMD: 0.30; 95% CI: –0.21 to 0.80; P = .25), oxygen consumption (SMD: –0.04; 95% CI: –0.33 to 0.25; P = .80), resting systolic blood pressure (MD: –2.84; 95% CI: –8.46 to 2.78; P = .32), systolic blood pressure after exercise (MD: –4.66; 95% CI –15.66 to 6.34; P = .41), resting diastolic blood pressure (MD: 0.89; 95% CI: –4.41 to 6.19; P = .74), diastolic blood pressure after exercise (MD: –0.21; 95% CI: –5.51 to 5.10; P = .94), heart rate (MD: –2.52; 95% CI: –7.76 to 2.73; P = .35), and arterial oxygen saturation (MD: –0.44; 95% CI: –2.38 to 1.49; P = .65). No severe adverse effects from nitrate supplementation were reported in the included trails. CONCLUSION: Current evidence suggests that nitrate supplementation may be safe but ineffective for improving exercise tolerance in people with COPD.