Testosterone Level

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It is thought that high testosterone (androgen) levels may increase the ability of SARS COV-2 to enter the cells and thus result in a more severe illness, which might explain why men have worse clinical outcomes than women

The virus uses two human proteins TMPRSS2 (Transmembrane Protease Serine 2) and ACE2 to enter human cells. First the virus uses ACE2 to enter the host cell and then the viral spike protein is primed by TMPRSS2. So if the number of TMPRSS2 molecules in cells can be reduced by lowering testosterone then the severity of COVID-19 might be reduced, a study by Columbia University has found.

TMPRSS2 varies a great deal between individuals with a recent study reporting that lung cells of men have higher levels.  In addition another study of 122 men in hospitals in Madrid found that 79% had male pattern baldness which was a higher proportion than would be expected for their age. Androgens influence baldness which might make bald men particularly vulnerable. 

It could also affect older people as they also have higher levels of TMPRSS2.

Androgens also regulate the immune response so the level of these could be responsible for what happens when the body fights the virus. High levels may produce a cytokine storm which is caused by an overactive immune system which has been seen in many severe cases of COVID-19.