Susceptibility of men to SARS-CoV-2 may be caused by sex differences in ACE2 expression

Experts have noted important aspects regarding the clinical symptoms of coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). For instance, the clinical symptoms are clearly different between the sexes. Men have higher SARS-CoV-2 infection rates than women. COVID-19 symptoms are also likely to be more severe in men than in women. Consequently, SARS-CoV-2-infected men experience fatal complications. The research results of medical experts highlight two possible reasons for the difference in COVID-19 clinical symptoms between the sexes: the risk derived from lifestyle patterns and the biological (immune response) risk. However, with regard to COVID-19, researchers are still unable to answer many questions regarding why the infection and fatality rates of men are higher than those of women. In this review, the authors report differences in blood levels of angiotensin-converting enzyme 2 as a reason for the differences between the sexes seen in COVID-19 symptoms including the most up-to-date information.