The expression of ACE2 has been detected in nasal epithelial cells, alveolar epithelial type II cells of lungs, and the luminal surface of intestinal epithelial cells

The nose, lungs, and intestine facilitate viral entry and serve as a potential site of viral invasion

However, it appears the expression of TMPRSS2 determines the ability of the virus to enter the cells

Research has suggested that age, sex, and genetic variants in the ACE2 gene can potentially affect ACE2 levels in the body

Children generally have higher levels of ACE2 than adults. Women have been found to have higher ACE2 levels than men due to the upregulation of ACE2 by estrogen

This could be the foundational reason men and post-menopausal women are more susceptible to COVID-19

One study of 534 subjects found that 67% of the variation in circulating ACE2 could be accounted for by genetic factors. Among different polymorphisms, it has been speculated that ACE2 rs2106809 might exhibit primary effects on the ACE2 levels. The circulating ACE2 levels tend to be greater in AA or AG genotype compared with that in the GG genotype.

How do you increase ACE2 expression? Potassium, vitamin D, and resveratrol. What was interesting about resveratrol is that it mitigated the effect of a high-fat diet by increasing the expression of ACE2 in animal studies. Betulinic acid (chaga mushroom) and oleanolic acid (olive oil) have also been studied as SARS-CoV-2 entry inhibitors.