The study, published in the journal Trends in Endocrinology and Metabolism, analysed existing research to look at reasons why Covid-19 symptom severity and mortality are more frequent in men than in women and in older people.

 

"The paper suggests female reproductive steroids play a protective role," said study author Graziano Pinna from the University of Illinois at Chicago in the US.

 

Female reproductive steroids, estrogen and progesterone and its physiologically active metabolite, allopregnanolone, provide anti-inflammatory functions, reshape competence of immune cells, stimulate antibody production and promote respiratory epithelial cell repair,

 

It also inhibits the ACE2 receptor, the door of access for the novel coronavirus (SARS-CoV-2) to infect the organism, suggesting they may protect against Covid-19 symptoms,

 

Pinna became interested in the role of reproductive steroids in Covid-19 pathology in March when early case reports showed Covid positive pregnant women who had no Covid symptoms, had escalated symptoms -- severe enough to require intensive care -- immediately after giving birth.

 

The severity of symptoms coincided with a rapid drop of estradiol, progesterone, and allopregnanolone.

 

"Hormones that help sustain the pregnancy -- like progesterone -- are 100 times more concentrated in a pregnancy's third trimester," Pinna said.

 

Estradiol, allopregnanolone, and progesterone all have important anti-inflammatory functions and are involved in resetting the immune system.

 

"This suggests that pregnant women became symptomatic, and some were even admitted to the ICU, after delivering their babies because of the rapid drop in these hormones. The correlation was really striking," he added.

 

Pinna's paper also discusses the importance of reproductive hormones in stimulating the production of antibodies and promoting lung cell repair after virus infection and fighting against the 'cytokine storm'.

 

Cytokine storm is -- an immune response where the body starts to attack its own cells and tissues rather than just fighting off the virus.

 

"Progesterone and allopregnanolone can block the incredible overreaction of the inflammatory system, repressing it and avoiding the over-expression of pro-inflammatory cytokines," said Pinna.