Meta-Analysis

. 2021 Jul 9;18(1):55.

doi: 10.1186/s12970-021-00450-4.

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

Chloe Gao¹, Saurabh Gupta², Taranah Adli³, Winston Hou⁴, Reid Coolsaet⁵, Abigail Hayes⁶, Kevin Kim^{7

8}, Arjun Pandey⁴, Jacob Gordon⁴, Gurneet Chahil^{9

10}, Emilie P Belley-Cote^{9

11}, Richard P Whitlock^{12

13

14

15}

Affiliations

¹ Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
² Department of Surgery, McMaster University, Hamilton, Ontario, Canada.
³ Faculty of Biomedical Sciences, University of Western Ontario, London, Ontario, Canada.
⁴ Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.
⁵ University of Guelph, Guelph, Ontario, Canada.
⁶ Queen's University, Kingston, Ontario, Canada.
⁷ Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.
⁸ Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, Ontario, Canada.
⁹ Population Health Research Institute, Hamilton, Ontario, Canada.
¹⁰ Saint James School of Medicine, Park Ridge, USA.
¹¹ Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
¹² Department of Surgery, McMaster University, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹³ Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹⁴ Population Health Research Institute, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹⁵ David Braley Cardiac, Vascular and Stroke Research Institute, 237 Barton St. E., Hamilton, Ontario, L8L 2X2, Canada. richard.whitlock@phri.ca.

PMID: 34243756
PMCID: PMC8268374
DOI: 10.1186/s12970-021-00450-4

Meta-Analysis

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

Chloe Gao et al. J Int Soc Sports Nutr. 2021.

. 2021 Jul 9;18(1):55.

doi: 10.1186/s12970-021-00450-4.

Authors

Affiliations

¹ Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
² Department of Surgery, McMaster University, Hamilton, Ontario, Canada.
³ Faculty of Biomedical Sciences, University of Western Ontario, London, Ontario, Canada.
⁴ Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.
⁵ University of Guelph, Guelph, Ontario, Canada.
⁶ Queen's University, Kingston, Ontario, Canada.
⁷ Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada.
⁸ Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, Ontario, Canada.
⁹ Population Health Research Institute, Hamilton, Ontario, Canada.
¹⁰ Saint James School of Medicine, Park Ridge, USA.
¹¹ Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
¹² Department of Surgery, McMaster University, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹³ Department of Health Research Methods, Evidence and Impact, McMaster University, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹⁴ Population Health Research Institute, Hamilton, Ontario, Canada. richard.whitlock@phri.ca.
¹⁵ David Braley Cardiac, Vascular and Stroke Research Institute, 237 Barton St. E., Hamilton, Ontario, L8L 2X2, Canada. richard.whitlock@phri.ca.

PMID: 34243756
PMCID: PMC8268374
DOI: 10.1186/s12970-021-00450-4

Abstract

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 VO_2max or blood lactate levels.

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

Keywords: Endurance exercise; Nitrate supplementation; Systematic review and meta-analysis.

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Conflict of interest statement

Dr. Whitlock reports grants from Bayer, Roche, and Boeringer-Ingelheim outside the submitted work. He also reports speaker honorarium from Boeringer-Ingelheim and consultancy for AtriCure and PhaseBio outside the submitted work.

Dr. Belley-Cote reports grants from Bayer and Roche outside this submitted work.

The other authors have no conflict of interest.

Figures

**Fig. 1**
Possible mechanisms of effect of nitrate on athletic performance

**Fig. 2**
PRISMA flow diagram for study selection

**Fig. 3**
Forest plot for power output in watts for nitrate supplementation versus placebo. Square markers represent mean difference for individual studies, with square size proportional to the weight given to each study in the meta-analysis. Horizontal lines indicate 95% confidence intervals (CI). The solid diamond represents the estimated 95% confidence interval for effect size of all meta-analyzed data

**Fig. 4**
Forest plot for time to exhaustion in seconds for nitrate supplementation versus placebo. Square markers represent mean difference for individual studies, with square size proportional to the weight given to each study in the meta-analysis. Horizontal lines indicate 95% confidence intervals (CI). The solid diamond represents the estimated 95% confidence interval for effect size of all meta-analyzed data

**Fig. 5**
Forest plot for distance travelled in metres for nitrate supplementation versus placebo. Square markers represent mean difference for individual studies, with square size proportional to the weight given to each study in the meta-analysis. Horizontal lines indicate 95% confidence intervals (CI). The solid diamond represents the estimated 95% confidence interval for effect size of all meta-analyzed data

**Fig. 6**
Forest plot for VO₂ in litres/minute for nitrate supplementation versus placebo. Square markers represent mean difference for individual studies, with square size proportional to the weight given to each study in the meta-analysis. Horizontal lines indicate 95% confidence intervals (CI). The solid diamond represents the estimated 95% confidence interval for effect size of all meta-analyzed data

**Fig. 7**
Forest plot for VO_2max in litres/minute in kilojoules for nitrate supplementation versus placebo. Square markers represent mean difference for individual studies, with square size proportional to the weight given to each study in the meta-analysis. Horizontal lines indicate 95% confidence intervals (CI). The solid diamond represents the estimated 95% confidence interval for effect size of all meta-analyzed data

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

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

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