We may wear face masks and carry hand sanitiser in our attempts to ward off Covid-19, but our bodies have an invisible protection that could be the most effective defense of all: our hormones.
This is something that menopause specialist Dr Louise Newson has been observing with female patients at her Newson Health Menopause and Wellbeing Centre in Stratford upon Avon. She has seen a pattern emerge among women who are taking HRT when it comes to their experiences of Covid-19.
"We've had several women who experienced less severe symptoms of Covid-19 than their male partners," Dr Newson explains. "I'm wondering if a woman's immune system when she is taking HRT is so good that it just deals with this virus more effectively."
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Dr Newson's anecdotal observation is something that has brought her together with Professor Tim Spector and NHS England to put her theory to a more robust test.
Professor Spector's Covid Symptom Study is the world's largest citizen science project. Currently, more than 3.6 million people have downloaded the app and are logging their daily symptoms. Now, hormonal questions have been added into the mix. "The app has been updated with specific questions about periods, hormone medications and menopause," says Dr Newson.
"We want to understand how hormones such as oestrogen might influence Covid-19 outcomes. Many studies have shown that Covid-19 affects men more severely than women, and we already know that oestrogen has a beneficial effect on the immune system. Oestrogen receptors are on every cell in a woman's body and this hormone affects how the cells respond and how they fight infections. It means women fight viruses better than men."
This isn't just true for the HRT-taking women who Dr Newson sees in her clinic. "Women who are pregnant have very high levels of oestrogen and progesterone, and they seem to have some protection against Covid-19," says Dr Newson. "So it makes sense for us to think, is it related? Is oestrogen dampening down the immune response to Covid-19 and protecting women who are pregnant, or taking the contraceptive pill, having regular periods or taking a form of HRT? I'm not naïve enough to think that lack of oestrogen is the only reason that people end up in intensive care, but I think it's a part of the picture that we can't ignore."
For Dr Newson's clinic patients of menopausal age, which is an average of 51 in the UK, it is particularly important to understand the oestrogen and Covid-19 connection.
"In women, the increased risk from Covid-19 starts in her late 50s, which is younger than the risk starts in men," says Dr Newson. "With the Covid Symptom Study we're looking to see whether this is related to the menopause, because if she's in her late 50s and not on taking HRT, then she will be oestrogen deficient – hence, perhaps, at higher Covid-19 risk."
It's a topic of special interest to those of us keen to raise awareness of the health benefits of HRT. As the founder of MPoweredwomen.net, a site dedicated to busting menopause taboos and giving women the facts not the fictions, I'm hopeful that this research might help dismiss, once and for all, the scaremongering that puts so many women off taking HRT.
I'm not alone. Dr Stephanie Goodwin, a London GP and menopause specialist is determined to change the HRT conversation.
"Too many women are put off taking HRT because of lack of knowledge and unfounded fears," she says. "The benefits of HRT far outweigh the risks. If the research being done by Dr Newson and Professor Spector can show that oestrogen helps with immunity against Covid-19, then that will be positive news for menopausal women."
Dr Goodwin has a personal interest in the research, having been struck by the virus herself last month. "As a woman on HRT, my own Covid 19 experience was very mild," she says. "I was certainly very happy with my immune response. If that is due to the oestrogen in my HRT, then that can only be a good thing."
The effects of oestrogen on Covid-19 have been signalled by other studies. "There's some research looking at women in Wuhan who have had Covid-19," says Dr Newson. "The women with lower oestrogen levels had more severe symptoms of the disease, which is really interesting."
Oestrogen and HRT is not, of course, an option for men. But oestrogen is not the only hormone being investigated for its positive effects on immunity against Covid-19. The role of testosterone is also being examined.
Professor Geoff Hackett is a Consultant in Urology and Professor in Sexual Medicine at Aston University. He's been studying the impact of testosterone levels on men's susceptibility to diabetes, heart disease and chronic kidney disease, for years. Now, the link with Covid-19 is under examination.
"Studies in Germany, Italy and China have been measuring the testosterone levels of men when they arrive in hospital with Covid-19," says Professor Hackett. "We know that Covid-19's entry into the man's body is via the testes, where it causes an attack on the immune system and a plummeting of testosterone levels. They drop like a stone."
The studies' results are stark. "The men who died were the ones with the lowest levels of testosterone on admission into hospital," says Professor Hackett. "If you've come into hospital with an already low testosterone level, this additional acute insult finishes you off. Covid-19 kills with something called a cytokine storm, when inflammation agents destroy the arteries and lungs. Because testosterone is an important anti-inflammatory, it has immunity effects against that storm."
Professor Hackett also points to a possible link between low testosterone levels and the higher death rates from Covid-19 in BAME communities. "Men from South Asia have testosterone levels that are about 10 per cent lower than equivalent UK men," he says. "Afro Caribbean men drop their testosterone much more steeply from the age of about 30. Everything fits because the exact groups of men with higher mortality rates are the exact groups who have lower levels of testosterone."
Professor Hackett is clear on what all middle-aged men should do. "Ask your GP to test your testosterone level," he says. "The likely symptoms will include low libido and sexual dysfunction. But other symptoms are lack of energy, lack of motivation, some loss of strength and poor sleep, particularly difficulty in getting off to sleep. Men might also have night sweats if their testosterone gets very low – something that women with low oestrogen know all about."
What is clear, from both Dr Newson and Professor Hackett, is that whether you're a man or a woman, your hormone health could be a key factor in managing your response to Covid-19.
"If taking oestrogen via HRT improves women's immunity then it means that a lot of menopausal women who are working on the front line can go back to work more confidently," says Dr Newson. "The HRT may improve their immunity and give them some protection."
As for the men. "Of course we need a vaccine if we can get it," says Professor Hackett. "But it looks as though a man has a much greater chance of surviving this enemy and others if he goes into the battle with a normal testosterone level."