TABLE 3.

Summary of current knowledge, limitations and prospects for metabolomics and microbiome studies of obstructive sleep apnoea (OSA)

	Summary of findings	Limitations	Prospects
Metabolomics	Increased levels of anaerobic metabolites and oxidation products Disrupted lipid metabolism	Few relevant studies Small sample sizes Lack of strict control of confounding variables Sensitive to complications Lack of comparability due to different biofluids and platforms	Standardised technologies and software as gold standards for future studies Prospective studies strictly adjusting for confounding variables To explore functional annotation of unknown metabolites and microbiota in various body fluids or cavities To focus on microbial and metabolic signatures specific to OSA versus those common to other metabolic diseases To elucidate casual relationships between metabolomics and the microbiome More multi-omics studies using advanced approaches
Microbiome	Emergence of dysbiosis in cases of IH Decrease in the relative abundance of SCFA-producing bacteria in OSA-induced hypertension High susceptibility to OSA in Prevotella enterotype patients Changes in oral, nasal and lung microbiome profiles	Few relevant human studies Difficulty of extrapolating animal model results to patients Sensitive to external factors and complications Different analysis sites leading to differences in microbial profiles

IH: intermittent hypoxia; SCFA: short-chain fatty acid.