Causal Relationships Between Short-Chain Fatty Acids and L-isoleucine Biosynthesis and Susceptibility and Severity of COVID-19: Evidence from Mendelian Randomization.

Recently, we read a paper by Qiu and colleagues with interest, who reported potential causal candidates for COVID-19 in 123 blood metabolites by Mendelian randomization (MR).1 In Journal of Infection and other journals, the association between altered gut microbiota composition and Coronavirus disease 2019 (COVID-19) has been broadly discussed, whereas such association was based on observational studies without clear cause or consequence effect established, likely to be potentially biased by confounders.