Men who contract Covid-19 treble their risk of developing erectile dysfunction, according to new research.
Doctors at the University of Rome asked 100 men, with an average age of 33, to report recent problems with sexual function.
Nine per cent of those who had not had Covid said they'd had difficulties.
But among those who had been infected the figure was 28 per cent, according to a report in the journal Andrology.
Researchers said the virus is known to cause inflammation in the endothelium — the inner lining of blood vessels throughout the body.
Arteries supplying the genitals are small and narrow, so any inflammation is likely to disrupt blood flow and impede a man's sexual response.
This is the latest piece of research to find that, in many ways, men fare worse with a Covid infection than women — they are more prone to serious symptoms and 1.7 times more likely to die of the virus.
Some experts have suggested differences in levels of the sex hormones oestrogen and testosterone may partly explain this.
Men who contract Covid-19 treble their risk of developing erectile dysfunction, according to research by the University of Rome
On average, women in the UK live 3.7 years longer than men, even in non-Covid times — and oestrogen is thought to be key, improving women's immune function and helping to protect the cardiovascular system.
High testosterone levels may increase some risks to the cardiovascular system, which is put under huge pressure by coronavirus.
Could a toxic soup of chemicals in everyday life be destroying men's ability to father children?
That is the latest claim from a U.S. expert, Dr Shanna Swan, who made headlines in 2017 with research that suggested human sperm counts are plummeting.
Dr Swan, a professor of environmental medicine and public health at the Icahn School of Medicine, New York, made her original claim in the journal Human Reproduction Update.
Her analysis of previous research evidence concluded that men's reproductive problems are increasing by at least 1 per cent a year in Western countries.
These problems include declining sperm counts, falling testosterone levels and increasing rates of testicular cancer.
Now, in a new book entitled Count Down, Dr Swan blames this crisis on male babies being harmed in the womb by their mothers' exposure to hormone-altering chemicals in food and many consumer items.
These chemicals include phthalates (used to make plastics more flexible and found in hundreds of products including toys, detergents, food packaging, personal-care products and electronic devices), bisphenol A (in plastic food containers) and flame retardants (used in furnishings, carpets and cars).
Dr Swan says these chemicals began to be produced in increasing quantities from 1950, after which male fertility began to drop.
'Sperm counts have declined by 50 per cent in just 40 years,' she says. 'It's difficult to deny how alarming this is.'
But new research offers another insight: not about how our sex hormones may help us fight Covid, but how the virus may interfere with their production, causing knock-on effects.
'One of the devious ways the virus gets into the body is by its spike protein binding to a receptor found at quite high concentrations not only in the lungs but in the reproductive organs,' explains Dr Channa Jayasena, a consultant in reproductive endocrinology and andrology at Hammersmith Hospital in London.
'When Covid-19 binds to these receptors, they can no longer perform their normal function.'
These ACE2 receptors are found throughout the body, most widely in the lungs and cardiovascular system as well as at high levels in the testes.
While the evidence is thin, Dr Jayasena suggests Covid-19 may leave men with lowered testosterone levels and could affect women's menstrual cycles and menopause, too.
All this has a potential impact on both fertility and general health, as sex hormones are involved in processes throughout the body, from muscle growth to immune function.
A review of 24 studies on male fertility and Covid-19, published last year in the World Journal of Men's Health, noted that patients who had suffered a moderate Covid infection had significantly lower sperm concentration, often for months after recovery, compared with those whose infection had been only mild.
But what came first, the low sperm count or the infection?
Shortly afterwards, another study, published in the journal The Aging Male, showed that not only might men with lower testosterone levels be at higher risk of getting Covid-19, but that the virus could indeed lower men's testosterone levels.
Mike Kirby, a former professor of general practice in Hertfordshire and editor of The Aging Male, suggests this means doctors should be ready to check testosterone levels in male Covid patients and, if necessary, provide testosterone replacement.
He says that without it, those men are at higher risk of cardiovascular problems, type 2 diabetes, muscular weakness and depression, and loss of sexual desire, function and fertility.
While this may be true, it is not yet clear whether coronavirus is affecting sex-hormone levels more than any other viral infection might, says Dr Jayasena, adding that in any case, any lowering of those hormones may well be temporary.
'If you had severe flu, then it might take at least another several weeks for your testes to start working properly,' he says.
'A man's sperm count can drop to zero during flu and it can take three months to recover fully. So I think it's reasonable to suggest a similarly severe illness such as Covid would do at least that.'