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Open Access 01-12-2023 | Nitrate | Systematic Review

Limited Effects of Inorganic Nitrate Supplementation on Exercise Training Responses: A Systematic Review and Meta-analysis

Authors: Austin C. Hogwood, Kara C. Anderson, Joaquin Ortiz de Zevallos, Craig Paterson, Arthur Weltman, Jason D. Allen

Published in: Sports Medicine - Open | Issue 1/2023

Abstract

Background

Inorganic nitrate (NO₃⁻) supplementation is purported to benefit short-term exercise performance, but it is unclear whether NO₃⁻ improves longer-term exercise training responses (such as improvements in VO_2peak or time to exhaustion (TTE)) versus exercise training alone. The purpose of this systematic review and meta-analysis was to determine the effects of NO₃⁻ supplementation combined with exercise training on VO_2peak and TTE, and to identify potential factors that may impact outcomes.

Methods

Electronic databases (PubMed, Medscape, and Web of Science) were searched for articles published through June 2022 with article inclusion determined a priori as: (1) randomized placebo-controlled trials, (2) exercise training lasted at least three weeks, (3) treatment groups received identical exercise training, (4) treatment groups had matched VO_2peak at baseline. Study quality was assessed using the Cochrane Risk-of-Bias 2 tool. Standardized mean difference (SMD) with 95% confidence intervals (CI) were calculated using restricted maximum likelihood estimation between pre- and post-training differences in outcomes. Moderator subgroup and meta-regression analyses were completed to determine whether the overall effect was influenced by age, sex, NO₃⁻ dosage, baseline VO_2peak, health status, NO₃⁻ administration route, and training conditions.

Results

Nine studies consisting of eleven trials were included: n = 228 (72 females); age = 37.7 ± 21 years; VO_2peak: 40 ± 18 ml/kg/min. NO₃⁻ supplementation did not enhance exercise training with respect to VO_2peak (SMD: 0.18; 95% CI: -0.09, 0.44; p = 0.19) or TTE (SMD: 0.08; 95% CI: − 0.21, 0.37; p = 0.58). No significant moderators were revealed on either outcome. Subset analysis on healthy participants who consumed beetroot juice (BRJ) revealed stronger trends for NO₃⁻ improving VO_2peak (p = 0.08) compared with TTE (p = 0.19), with no significant moderators. Sunset funnel plot revealed low statistical power in all trials.

Conclusions

NO₃⁻ supplementation combined with exercise training may not enhance exercise outcomes such as VO_2peak or TTE. A trend for greater improvement in VO_2peak in healthy participants supplemented with BRJ may exist (p = 0.08). Overall, future studies in this area need increased sample sizes, more unified methodologies, longer training interventions, and examination of sex as a biological variable to strengthen conclusions.

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Title: Limited Effects of Inorganic Nitrate Supplementation on Exercise Training Responses: A Systematic Review and Meta-analysis
Authors: Austin C. Hogwood
Kara C. Anderson
Joaquin Ortiz de Zevallos
Craig Paterson
Arthur Weltman
Jason D. Allen
Publication date: 01-12-2023
Publisher: Springer International Publishing
Keyword: Nitrate
Published in: Sports Medicine - Open / Issue 1/2023
Print ISSN: 2199-1170
Electronic ISSN: 2198-9761
DOI: https://doi.org/10.1186/s40798-023-00632-1

At a glance: The STEP trials

Springer Medicine

Limited Effects of Inorganic Nitrate Supplementation on Exercise Training Responses: A Systematic Review and Meta-analysis

Abstract

Background

Methods

Results

Conclusions

At a glance: The STEP trials

Springer Medicine

Abstract

Background

Methods

Results

Conclusions

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