New research adds to a growing body of evidence that suggests men are far more vulnerable to severe Covid-19 than women are.
Although both genders fall ill in the same numbers, men are 2.5 times more likely to get severe disease and die, the study from China showed.
The finding comes as scientists in New York and California are starting to test a novel hypothesis that sex hormones might play a part in disease severity.
Last week, doctors on Long Island started treating Covid-19 patients with oestrogen to boost their immune systems, The New York Times reported. And beginning next week, physicians in Los Angeles will start treating male patients with progesterone, a hormone that is predominantly found in women. Progesterone has anti-inflammatory properties and might prevent the immune system from overreacting, the researchers explained.
Hormones may not be the answer
"There's a striking difference between the number of men and women in the intensive care unit, and men are clearly doing worse," Dr Sara Ghandehari, a pulmonologist and intensive care physician at Cedars-Sinai in Los Angeles, told the Times. She is the principal investigator for the progesterone study.
But experts who study sex differences in immunity warned that hormones may not be the answer. Even elderly women with Covid-19 are outliving their male peers, despite drastic reductions in levels of hormones for women after menopause, they noted.
In the study from China, published on 29 April in the journal Frontiers in Public Health, the differences between men and women showed up early in the coronavirus pandemic.
"Early in January, we noticed that the number of men dying from Covid-19 appeared to be higher than the number of women," explained researcher Dr Jin-Kui Yang, a physician at Beijing Tongren Hospital.
"This raised a question: Are men more susceptible to getting or dying from Covid-19? We found that no one had measured gender differences in Covid-19 patients, and so began investigating," Yang said in a journal news release.
More research needed
Included in the study were 43 patients treated by Yang's team, plus data on an additional 1 000 Covid-19 patients. The researchers also looked at the records of 524 SARS patients from 2003.
According to one large Covid-19 dataset, more than 70% of the patients who died were male, which meant that men had 2.5 times the death rate of women.
Being a man was also a risk factor for more severe illness, regardless of age.
Men who had SARS were also more likely to die, compared with women, Yang's team noted. Also, men had higher levels of the ACE2 protein involved in both sicknesses, which may be an explanation.
Although more research is needed, Yang recommended that "additional supportive care and prompt access to the intensive care unit may be necessary for older male patients".