The effects of dietary nitrate supplementation on endurance exercise performance and cardiorespiratory measures in healthy adults: a systematic review and meta-analysis

Background Nitrate supplementation is thought to improve performance in endurance sports. Objective To meta-analyze studies evaluating the effect of nitrate supplementation on endurance sports performance among adults. Data sources We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, Web of Science and CINAHL without language restrictions. Methods We included studies that: 1) compared nitrate supplementation with placebo; 2) enrolled adults engaging in an endurance-based activity; and 3) reported a performance measure or surrogate physiologic outcome. We evaluated risk of bias using the Cochrane Collaboration tool and pooled data with a random-effects model. We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to evaluate confidence in estimates. Results We included 73 studies ( n = 1061). Nitrate supplementation improved power output (MD 4.6 watts, P < 0.0001), time to exhaustion (MD 25.3 s, P < 0.00001), and distance travelled (MD 163.7 m, P = 0.03). We found no significant difference on perceived exertion, time trial performance and work done. Nitrate supplementation decreased VO 2 (MD − 0.04 L/min, P < 0.00001) but had no significant effect on VO 2max or blood lactate levels. Conclusion The available evidence suggests that dietary nitrate supplementation benefits performance-related outcomes for endurance sports.