Clear differences: Although around the same number of men as women develop Covid-19, the death rate for men is around twice as high. A study in China found 2.4 times more deaths in men despite comparable previous illnesses and age distribution. In Europe too, more men than women die of SARS-CoV-2 infection. But why? So far, doctors can only speculate about the biological reasons.
The severity of infection with the SARS-CoV-2 coronavirus depends on several factors. Studies show that on average older people get Covid-19 more seriously than younger people and that the vast majority of severe cases suffer from pre-existing conditions such as high blood pressure, cardiovascular diseases, diabetes and obesity.
Men die of Covid-19 more often than women
But there is obviously another factor: gender. Evidence is now mounting that men are more at risk of Covid-19 than women. One team that has investigated the gender issue further is Jin-Kui Yang from Tongren Hospital in Beijing and his colleagues. They evaluated 43 of their own Covid cases and 1,059 case files of other Covid 19 cases treated in Wuhan.
The result: men and women were relatively equally represented in the diseases – but not in the deaths. Of these, 70 percent were men and just over 29 percent were women. “The mortality rate for men is 2.4 times higher than for women,” said Yang and his colleagues. “Men and women seem to be equally susceptible to Covid-19, but men are more likely to die from it.”
The same can be seen from European corona statistics: According to the WHO, 49 percent of around 380,000 Covid 19 cases registered in Europe are men – almost exactly half. However, 63 percent of those who died from the infection are men.
Is it because of the unhealthier lifestyle?
But why does it hit men harder? One hypothesis would be that men are already in poor health and have more previous illnesses. In fact, the incidence of cardiovascular disease, high blood pressure and the proportion of smokers among men is higher in most populations. However, in the study by Yang and colleagues, patients of both sexes had comparable previous illnesses, as they report. Men were not in worse shape than women before.
Hua Cai from the University of California at Los Angeles reports similarly after evaluating two further studies from China. He had examined whether it could be due to the proportion of smokers – in China 50 percent of men smoke but only around five percent of women. However, in the studies, only between one and twelve percent of the Covid-19 cases were smokers and the differences in the severity of the courses were not significant. That makes it unlikely that smoking is the explanation for the gender differences, said Cai.
Or the immune system?
But what is it then? A possible explanation is differences in the immune system. It has long been known that women have a stronger immune response to infections and vaccinations. Influenza and other viral diseases of the respiratory tract are therefore often more severe in men – the “male flu” is therefore quite real.
Researchers assume that this better protective effect in women is partly due to the sex hormones. Accordingly, estrogen and Co apparently promote the immune-mediated immune response to viruses – but only up to the menopause, as a 2011 study found.
From an evolutionary point of view, it could also be more favorable for viruses to make their female hosts less sick: mothers can then pass on the pathogens to their children. “For the pathogen, this additional transmission route makes the lives of hosts that allow vertical transfer more valuable,” explain London researchers Francisco Ubeda and Vincent Jansen, who investigated this phenomenon a few years ago.
Is the ACE2 receptor to blame?
But there could still be an explanation: the ACE2 receptor. This protein forms the docking site for SARS-CoV-2 and enables it to penetrate human cells. The receptor sits on cells of the lungs and the respiratory tract and also occurs in other organs such as the heart, nerves, intestines or kidneys. Doctors suspect that the number of these receptors affects how susceptible someone is to the virus.
And on this point, too, there seem to be differences between men and women, as Yang and his team report. “It has been shown that the levels of ACE2 in the blood of men are higher than in women – just as it is higher in diabetics and cardiovascular patients,” they report. The higher number of ACE2 receptors could also explain why more men died than women in the SARS pandemic: the pathogen at the time also docked on this receptor.
More studies needed
Overall, it seems plausible that there is a biological reason for the higher mortality rate among men in Covid-19. But the data is still too thin to be more than guessing what differences might be responsible.
“More clinical studies and basic research are needed to figure out the role of gender and other prognostic factors,” said Yang and his team. (Frontiers in Public Health, 2020; doi: 10.3389 / fpubh.2020.00152; The Lancet Respiratory Medicine, 2020; doi: 10.1016 / S2213-2600 (20) 30117-X; WHO Weekly surveillance Report)
Source: Frontiers, Lancet, Nature, WHO
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