Female Covid-19 patients face less severe disease complications and a lower risk of dying than male patients thanks to hormones and chromosomes that contribute to a stronger immune response, say researchers.
"The highlight of our study is how the sex differences in Covid-19 are linked to ACE2," said senior author Gavin Oudit from the University of Alberta in Canada.
ACE2 is the enzyme that acts as the receptor allowing SARS-CoV-2 to enter the body, but it is also key in protecting against cardiovascular, lung and kidney diseases.
"Because of their chromosomes, women have two copies of the ACE2 gene and men have only one copy," Oudit said.
This does protect them from the complications associated with the virus.
In the study, published in the American Journal of Physiology-Heart and Circulatory Physiology, the research team explained that ACE2 is an X chromosome-linked gene.
To avoid duplication, one X chromosome tends to be inactivated, but due to its location ACE2 escapes inactivation, meaning women have twice as many active genetic instructions to make ACE2.
Another gene that is twice as strong in women due to this X-inactivation escape is called Toll-like receptor seven, a key part of the innate immune system.
"The stronger presence of Toll-like receptor seven in women explains why women's immune systems are stronger than men's and can tolerate virus infection better, including the common cold," Oudit said.
"The man-cold phenomenon is real," Oudit added.
In the study, the researchers report that men face more severe illness and poorer outcomes around the world.
They noted that women likely face more exposure to SARS-CoV-2 than men -- for example, 70 per cent of healthcare workers are female -- but this is not reflected in their outcomes.
"Due to gender issues, women face more risk, so it's reassuring to know that their outcomes are not any worse; in fact they are clearly better than men's," Oudit said.