ABSTRACT
PURPOSE: This study aimed to systematically review the effect of nitrate supplementation on blood oxygen saturation. METHODS: We searched PubMed, Scopus, and Cochrane Library databases from their inception up to October 2022. Two reviewers independently conducted two stages of the screening process to include a randomized controlled trial with nitrate supplementation versus placebo intervention assessing oxygen saturation among lowlanders going to either real or simulated high altitude environments. We used the Cochrane Risk of Bias 2.0 tool to assess the risk of bias in the included studies. Fixed-effect model meta-analyses were conducted for laboratory-based studies. Random-effect meta-analyses were conducted for real-world studies. RESULTS: We found 7 trials that met the eligibility criteria. A meta-analysis of studies with some bias concerns showed an increase of 1.26% in the SpO2 with 44% I2 during submaximal exercise at simulated high altitudes (GRADE: low). On the contrary, a meta-analysis of studies without heterogeneity showed that nitrate supplementation aggravated oxygen saturation decline (-2.64%, p=0.03, GRADE: high) during rest in real high-altitude environments. A meta-analysis also showed that nitrate supplementation did not affect Acute Mountain Sickness (AMS) symptoms (GRADE: high). CONCLUSION: Our results suggest that nitrate supplementation did not provide benefits for AMS prevention during rest at high altitudes. The low-quality evidence showing small beneficial effects of nitrate supplementation during exercise calls for further studies.
