Men with longer ring fingers face a lower risk of dying from Covid-19 and are more likely to suffer mild symptoms, researchers claim.
Academics found coronavirus death rates in countries where men have shorter ring fingers were up to a third higher.
Ring finger length is determined by how much testosterone a foetus is exposed to when growing in the womb, the experts said.
The more testosterone a male is exposed to in the womb, the longer their ring finger will be, it is believed.
Testosterone is thought to be protective against severe Covid-19 by increasing the number of ACE-2 receptors in the body.
Scientists believe the coronavirus, officially called SARS-CoV-2, enters the body and causes infection through these receptors.
But studies have also suggested that high levels can protect against lung damage, meaning people with few receptors are at higher risk of viral infections.
The new study, carried out by Swansea University, found men with low testosterone levels are twice as likely to die of Covid-19 than men with higher levels.
Academics found coronavirus death rates in countries where men have shorter ring fingers were higher. The case fatality rate was an average of 4.9 (per 100,000) in the top 10 countries with the shortest finger length, including in Bulgaria, Argentina and Turkey. It was an average of 2.7 in the top 10 countries with the longest finger length, including Malaysia, Mexico and Russia
How to see if you have a long ring finger: Measure the index finger and the ring finger to the closest millimetre. The first measurement is divided by the second measurement to get the digit ratio. The smaller the digit ratio, the longer the ring finger is. The country with the smallest average male right hand digit ratio was Malaysia, with 0.976. The higher the digit ratio, the shorter the ring finger is. Bulgaria has the highest male right hand digit ratio, with 0.99
Researchers found that in countries where the right hand digit ratio was smaller, including Malaysia, Russia and Mexico, the case fatality rate was lower (left side)
Mounting evidence has shown men are more likely to die from the coronavirus than women – but scientists have been unable to determine exactly why this is.
In England and Wales, the Covid-19 death rate for men is 97.5 per 100,000 people compared to 46.5 for females, according to the Office for National Statistics.
Scientists believe men are less likely to wash their hands, may not seek medical help, and have more underlying health conditions that make them more vulnerable.
But testosterone could be one of the key reasons why so many men are dying from coronavirus, doctors believe.
Swansea University experts added to the theory that men who have low testosterone levels are at more at risk of Covid-19 than other men.
They looked at data of 200,000 people in 41 countries where the researchers had already measured the finger lengths of volunteers.
Some researchers believe finger lengths reflect a foetus’s exposure to testosterone and other hormones that guide development in the womb.
The index finger and the ring finger was measured to the closest millimetre. The first measurement is divided by the second measurement to get the 2D:4D ratio.
The smaller the digit ratio, the longer the ring finger is. The country with the smallest average male right hand digit ratio was Malaysia, with 0.976.
The higher the digit ratio, the shorter the ring finger is. Bulgaria has the highest male right hand digit ratio, with 0.99.
WHY ARE MALES MORE AT RISK OF COVID-19?
Several studies have reported a higher fatality rate in men compared with women.
Scientists hypothesise that men are less likely to wash their hands often, may not seek medical help, have a genetically disadvantaged immune system compared to women, or have more underlying health conditions that make them more vulnerable.
The disparity between adult men and women has largely been put down to behaviours, including drinking alcohol, smoking, and eating unhealthily.
Dr James Gill, a locum GP and honorary clinical lecturer, Warwick Medical School, said theories lie on the assumption that simply men don’t look after their bodies as well, with higher levels of smoking, alcohol use, obesity and other deleterious health behaviours.
These would put men at a higher risk of health conditions – which has been confirmed to be detrimental to COVID-19 outcomes.
The sex differential in smoking is especially marked in some countries such as China, where 50 per cent of men smoke compared to five per cent in women.
However, Dr Gill said: ‘Whilst smoking is a plausible factor, globally, across various different cultures, where smoking rates do differ, we are still seeing the sustained difference in mortality between men and women.
‘Whilst we don’t have a definitive answer on why there is a difference between how men and women respond a COVID19 infection at the immunological level – yet – currently it is a fair assumption that there will be a significant interplay between the biology and the environmental facts.’
The slight increase in boys being infected with coronavirus compared to girls cannot be the result of behaviours such as smoking.
Philip Goulder FMedSci, professor of immunology in the Department of Paediatrics, University of Oxford, explained how males and females have genetically different immune responses, which would be present from birth.
He said: ‘It is becoming increasingly recognised that there are substantial differences in the immune system between males and females and that these have significant impact on outcome from a wide range of infectious diseases.
‘Several factors contribute to this, but these include the fact that females have two X chromosomes compared to one in males, and a number of critical immune genes are located on the X chromosome.
‘In particular, the protein by which viruses such as coronavirus are sensed is encoded on the X chromosome. As a result, this protein is expressed at twice the dose on many immune cells in females compared to males, and the immune response to coronavirus is therefore amplified in females.’
This effect can be seen in how the body responds to vaccines.
The immune response throughout life to vaccines and infections is typically more aggressive and more effective in females compared to males, Professor Goulder said.
Researchers found that in countries where the male digit ratio was smaller, including Malaysia, Russia and Mexico, the case fatality rate of Covid-19 was lower.
And in countries where the male digit ratio was higher, including the UK, Bulgaria and Spain, the case fatality rate was higher.
Case fatality rate is how many people who die from Covid-19 after being diagnosed.
In the UK, official figures show the virus has a case-fatality ratio of around 11 per cent.
It is different to the mortality rate, which takes into consideration everyone who has ever been infected, including those with none or mild symptoms.
Case fatality rate at this stage of the pandemic is not considered entirely accurate because it relies on testing strategies identifying all cases, and this varies from country to country.
The case fatality rate for each nation in the study included women. However, the link between finger length and deaths was still there when women were removed from the statistics.
The findings were more significant when looking at the right hands of men than their left hands.
Women’s finger length didn’t seem to affect death rates, according to the study, published in the journal Early Human Development.
When looking specifically at the left hand, the top 10 countries with the longest male ring finger had an average case fatality rate of 3.1 per cent, compared to the 10 countries with the shortest ring finger, with an average fatality rate of 5 per cent.
And for the right hand, the top 10 countries with the longest ring finger had an average case fatality rate of 2.7 per cent, compared to the 10 countries with the shortest ring finger, with an average fatality rate of 4.9 per cent.
Lead researcher Professor John Manning, said this may give Australia, New Zealand, Austria and East Asian nations, where male ring fingers are longer, ‘a biological advantage’, The Sun reports.
He added: ‘Our findings may be men with long ring fingers will experience mild symptoms and could return to work.’
The researchers said that finger length is an indicator of how much testosterone a foetus was exposed to while growing.
Professing Manning said: ‘The theory is that someone with high prenatal testosterone — and a long ring finger — has greater levels of ACE2.
‘These concentrations are large enough to oppose the virus.’
Cell receptors called ACE-2, which coat the surfaces of cells, are what the coronavirus attaches to in order to infect our healthy cells.
It’s thought that the more of these receptors you have, the more entry points there are for the virus.
However, ACE-2 receptors are thought to limit disease progression once the coronavirus is in the body.
The virus is known to cause lung damage by depleting the numbers of ACE-2 receptors once inside the body.
HOW CAN YOU MEASURE YOUR 2D:4D RATIO?
A relatively long ring finger is a sign of exposure to higher levels of testosterone in the womb, while a relatively long index finger points to greater amounts of oestrogen.
One theory is that for a short time in foetal development, there are testosterone receptors on the fingers and that the ring finger may have more of these receptors and grow faster when exposed to it.
So, how do you measure your 2D:4D ratio?
For readers, there are several ways to figure out their 2D:4D ratio.
The new research uses an electronic caliper.
Respondents were asked to place their hands on a flat surface, palms facing upwards, and straighten out their fingers.
A researcher then measured the length of the index and ring fingers on both hands.
This measurement should be taken from the center of the fold between the finger and palm up to the very tip of the finger.
That way the upper lip of the caliper does not press against the finger.
Therefore, it seems that people who express high levels of ACE-2 may in fact be protected against disease severity.
Professor Manning wrote in his paper: ‘The ACE-2 gene is more strongly expressed in females compared to males.
‘These associations suggest a negative correlation between ACE-2 expression and Covid-19 fatality.
‘The down-regulation of ACE-2 may therefore be associated with poor prognosis from Covid-19.
‘Research suggests that testosterone in men (and estrogen in women) up-regulates ACE-2.’
The paper concludes: ‘A strong positive association between male 2D:4D (digit ratio) and mortality may provide a biomarker for male Covid-19 susceptibility and identify those for whom it would be advisable to exercise social distancing.’
A recent study found men with low testosterone levels that contract Covid-19 are at far greater risk of dying from the virus, a study has found.
Samples from the 45 Covid-19 patients in a German hospital were tested for 12 hormones, including testosterone and dihydrotestosterone.
Professor Gülsah Gabriel from the Leibniz Institute for Experimental Virology in Hamburg, who was involved in the research, told MailOnline: ‘The majority of male Covid-19 patients had low testosterone levels.
‘Of those male Covid-19 patients who died, the majority also had low testosterone levels.
‘Thus, low testosterone levels in men seem to be a risk factor for severe and even fatal disease outcome in men upon infection with so-called “cytokine inducing” respiratory viruses.’
Testosterone is known to help regulate the body’s immune response but when a man has low levels of testosterone, the immune system is not kept in check and can go haywire following infection.
This leads to a so-called cytokine storm which happens when the immune system goes out of control as it tries to kill the pathogen.
A cytokine storm eventually begins damaging the body itself and, if left unchecked, can be fatal.
Of the male Covid-19 patients sent to ICU at the German hospital, more than two thirds (68.6 per cent) recorded low levels of testosterone.
In contrast, the majority of female patients (60 per cent) had elevated testosterone levels.
While low levels of testosterone can not control the immune response in men, the study found that in female Covid-19 patients, higher testosterone levels were linked to a more significant inflammatory response.
WHAT HAVE STUDIES ON FINGER LENGTH SHOWN?
AFFAIRS – Women with long index fingers are more likely to have affairs
New research has shown women with long index fingers on their left hands are more likely to have affairs, a study has shown.
The findings have surprised scientists as having a longer index finger is associated with having more typical female characteristics.
The longer index finger and shorter ring finger have been linked to being exposed to higher levels of female sex hormones in the womb.
It was assumed that women who were ‘more feminised’ would be more likely to be satisfied with their romantic relationships, and to be less impulsive.
Being more exposed to the sex hormone oestrogen in the womb leads to women’s index fingers growing longer than their ring finger.
By contrast, being exposed to more of the male sex hormone testosterone in the womb has a more ‘masculinising’ effect – and results in a longer ring finger and a shorter index finger.
SEXUALITY – Women with longer ring fingers are more likely to be lesbian
Last month research found that women whose ring fingers are longer than their index digits more likely to be lesbian.
Researchers at Essex University looked at sets of identical twins where one of the siblings was heterosexual.
They found that the homosexual twin tended to have a greater difference between the length of their index and ring finger, with the difference most pronounced among women.
Previous research has indicated that exposure to the male hormone testosterone in the womb could be linked to differences in finger length and also to sexuality.
Women’s index and ring fingers are typically of similar length while in men there is a greater difference.
Both men and women are exposed to the ‘male’ hormone testosterone in the womb.
VOICE – Babies are more likely to have squeaky voices if the index finger is longer than their ring finger
Earlier this year scientists found there could be a link between the length of a child’s fingers and the pitch of their voice.
A baby is more likely to grow to have a squeaky voice if the index finger on their right hands is longer than the ring finger, the research suggested.
Similarly, scientists said the connection is probably the result of a lack of testosterone in the womb.
Testosterone is known to be key to early body growth and plays an important role in how vocal pitch develops during puberty.
JOB – Women with long ring fingers are more likely to have a traditionally female job
A woman’s choice of career is linked to the length of her fingers, according to a study.
Women whose index finger was short compared to their ring finger were more likely to have what was regarded as a traditionally male job, such as a lawyer or a manager in industry, the researchers found.
And those whose index finger was longer than their ring finger were more likely to be employed in a stereotypically female career, such as nursing or primary school teaching.
For the study, researchers from the National Research University in Russia analysed data from 1,500 men and women whose fingers were measured using digital callipers.
They found that significant differences in the 2D:4D differences were observed only for women and mostly for the left hand.
SHARING – Children with longer ring fingers are less likely to share
Children who have index fingers shorter than their ring fingers are less likely to share their toys, research suggests.
Evidence already exists to show they are more aggressive – but the new study shows they are also more selfish – and won’t even share with friends.
It is known those who have an index finger that is shorter than their ring finger are exposed to greater amounts of testosterone in the womb because the hormone affects the development of finger length.
Anthropologists argue that higher levels of the hormone during pregnancy leads to a ‘masculinisation effect’ in both boys and girls. Testosterone levels remain high as children age.
Austrian experts observed the habits of dozens of boys and girls given the choice of who gets glittery stickers to make the conclusion.