Are women really the stronger sex?
Statistics show men are more likely to die from Covid-19 and it’s down to fundamental differences in our chromosomes, as JANE SYMONS discovers
WITH twice as many men as women dying from Covid-19, the pandemic is proving that “man flu” is not a myth and – when it comes to immunity – women really are the stronger sex.
But having a hyper-vigilant and very aggressive immune system has its downsides – it puts women at greater risk of autoimmune conditions such as multiple sclerosis, rheumatoid arthritis and coeliac disease.
Now, some experts believe these sex-based divides in health and immunity hold the key to conquering not only coronavirus, but many health challenges.
X VERSUS Y
When the first figures emerged from China they showed that although coronavirus infection rates were almost the same for men and women, two-thirds of those dying were men. Initially, this was put down to the fact that 62 per cent of Chinese men have smoked, compared to just three per cent of women there.
But this theory began to unravel as similar patterns in Covid-19 deaths emerged in Europe and America, where many more women smoke.
Professor Sarah Hawkes, director of the Centre for Gender and Global Health at University College London, says: “What Covid-19 is throwing into stark relief is that there are differences. But it is important to understand the difference between sex and gender – sex is biological, while gender relates to socially constructed differences.”
Gender differences in lifestyle factors such as smoking, diet and alcohol consumption explain some of the health disparities between men and women. But biology, particularly having two X chromosomes, ensures women really are the fittest when it comes to survival.
Dr Sharon Moalem, an awardwinning genetics researcher and bestselling author who has spent decades studying this phenomenon, explains: “X chromosomes contain around 1,000 different genes and many are involved in the immune system.
“But the male Y chromosome has only around 70 genes, which are mostly involved in sperm production.”
As a result, women not only have two different versions of many immune system genes, these genes also work together and swap genetic information. Dr Moalem says: “It’s like having a toolbox with two of every tool; two different size screwdrivers, two hammers and two wrenches.
“On top of this, female cells work together, side by side.They have the ability to make a tool and share it with their sister cell,” he adds. Hormones play a part, too. Dr Kyle Sue, Clinical Assistant Professor in Paediatrics and Family Medicine at the University of Alberta in Canada, says: “Oestrogen tends to be protective, in that it increases the work the immune system is able to do to fight infection, whereas testosterone seems to do the opposite.”
And these differences mean that men and women are dealt very different hands when it comes to health.
The XX-factor gives females an advantage before they are even born. Early miscarriage is more common when women conceive a boy, while pregnancy complications such as preeclampsia and placental problems are also more common when women are carrying a boy.
Around 55 per cent of babies born before 32 weeks are boys and this rises to around 60 per cent for very premature babies. Boys born prematurely are also more likely to suffer lasting damage such as cerebral palsy and cognitive damage.
One reason for this could be premature girls have higher levels of catecholamine, a fight-or-flight hormone which primes the body for physical activity.
The most obvious example of female survival superiority is life expectancy. The Office for National Statistics calculates that, on average, a toddler will live to be 79.3 years old if they’re a boy, but 82.9 years if they’re a girl. Similarly, a 65-year-old man can expect to live another 18.6 years but a woman the same age will have another 21. Only one in five men makes it to their 90th birthday, compared to one in three women. Danish researchers who studied records from seven famines and epidemics found women are
“the life-expectancy champions” and lived longer in every case.
HEART OF THE MATTER
Men have a 29 per cent higher risk of developing heart disease and are more likely to have cardiac disease before their 50s.
In part this is because of lifestyle: they are more likely to be overweight, drink to excess and smoke. But hormones are a factor, too. Until menopause, women are protected by their higher levels of oestrogen, with studies confirming the hormone reduces oxidative stress, blood pressure and fibrosis, as well as improving the elasticity of blood vessels. Conversely, testosterone appears to increase cardiac risk by suppressing HDL cholesterol.
Yet men are more likely to survive their first heart attack. As heart disease is still seen as a “male” problem, women often delay seeking help and, when they do, they are 50 per cent more likely to be misdiagnosed.
Symptoms vary, too. Men usually report crushing chest pain, while women sometimes describe this as tightness or dismiss it as indigestion.
Having an aggressive immune system puts women at greater risk of autoimmune disorders. MS is three times more common in women than men; for every nine women with lupus, only one man is affected; and, under the age of 50, the incidence of rheumatoid arthritis is four to five times higher in women. But Dr Moalem says women still have an edge. “Even though they are more likely to be affected by autoimmune conditions, compared to the men who get them, women do much better.” One study found men had an average MS severity score of 5.11 while the average for women was just 3.02.
Studies of vaccines, including the MMR, the BGC for TB and the combined tetanus, diphtheria and pertussis shot show women have a much stronger immune response. A large American study of flu jabs found women got two or three times more protection than men from the same dose. Women are also more likely to have side effects, prompting some experts to argue they should have lower doses.
Women are more likely to seek help for pain problems and appear to be more susceptible to migraine and neuropathic pain.
There is also evidence that men and women feel pain in different ways. Some studies suggest women have a higher pain threshold. When they have access to self-administered opioids following surgery, men give themselves higher doses – even though studies show women need higher doses of morphine to get the same relief.
BODY OF EVIDENCE
Men have a higher proportion of muscle, so burn more calories. Men need 2,500kcal a day, while women need only 2,000.Women are more efficient at storing fat, and have six to 11 per cent more body fat. It’s an evolutionary safeguard to ensure they could conceive and breastfeed when food was in short supply.
Because women have more body fat and less water, if a man and woman of the same weight drink the same amount of alcohol, the woman will have higher blood alcohol reading.
● Help scientists find out why men are more at risk of Covid19 by joining the CovidenceUK study (qmul.ac.uk/covidence)