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 VO2 (MD - 0.04 L/min, P < 0.00001) but had no significant effect on VO2max or blood lactate levels.

CONCLUSION: The available evidence suggests that dietary nitrate supplementation benefits performance-related outcomes for endurance sports.