Ergogenic Effect of Nitrate Supplementation in Clinical Populations: A Systematic Review and Meta-Analysis.

Inorganic nitrate (NO) supplementation, via its conversion to nitric oxide (NO), has been purported to be ergogenic in healthy individuals. Many disease states are characterized by reduced NO bioavailability and are expected to derive a benefit from NO. This systematic review and meta-analysis evaluate the current literature on the ergogenic effect of NO supplementation in individuals with cardiopulmonary and metabolic diseases (CPMD). Relevant databases were searched up to December 2023 for randomized, placebo-controlled crossover trials for aerobic exercise outcome variables with CPMD. Twenty-two studies were included, and 46% reported ergogenic benefits of inorganic nitrate supplementation. NO supplementation had no effect on aerobic performance with respect to maximal (SMD = 0.11, 95% CI: -0.12 to 0.34, = 0.34) and submaximal (SMD = 0.16, 95% CI: -0.13 to 0.46, = 0.27) TTE, VO (SMD = 0.002, 95% CI: -0.37 to 0.38, = 0.99), or 6MW (SMD = 0.01, 95% CI: -0.29 to 0.28, = 0.96). When the studies were limited to only cardiovascular disease conditions, NO supplementation had trivial effects on aerobic performance with respect to Timed Trials (SMD = 0.14, 95% CI: -0.04 to 0.33, = 0.13), VO (SMD = -0.02, 95% CI: -0.32 to 0.27, = 0.87), and small effects on Distance Trials (SMD = 0.25, 95% CI: -0.18 to 0.69, = 0.25). Sunset funnel plots revealed low statistical power in all trials. The results of this systematic review revealed that 46% of the individual studies showed a positive benefit from inorganic nitrate supplementation. However, the meta-analysis revealed a trivial effect on physical function in CPMD populations. This is likely due to the large heterogeneity and small sample sizes in the current literature.