The effect of acute normobaric hyperoxia on cognition: A systematic review, meta-analysis and meta-regression

This systematic review, meta-analysis and meta-regression examined the effect of acute normobaric hyperoxic breathing on cognition in healthy humans. 23 studies were included providing 76 effect estimates (EE). Hyperoxic breathing improved memory accuracy (22 EEs; g = 0.34) and speed (9 EEs; g = 0.59), attention accuracy (7 EEs; g = 0.59) and speed (7 EEs; g = 0.51), reaction speed (8 EEs; g = 0.82), crystallised intelligence (7 EEs; g = 0.73), executive function (6 EEs; g = 0.88) and information processing (10 EEs; g = 0.62). However, the overall quality of evidence was low (average Rosendal score of 47%) and there was a large range of study heterogeneity, with prediction intervals often crossing 0; therefore, reducing the reliability of the magnitude of these favourable effects. Oxygen percentage, 100% compared with 22-99% oxygen, temporal position of administration to task performance, and study quality did not influence the overall weighted mean effects for most cognitive domains. Altogether, despite beneficial results, further high quality research is required prior to recommending hyperoxic breathing to enhance cognition.