Senile sperm and the male biological clock
Itís long been a pub boast that a man can still produce children at 90, while women only have until the menopause. But now research suggests menís reproductive health may be just as much at the mercy of time as womenís.
US researchers at the University of Washington, in Seattle, found that men also have a form of biological clock, and that beyond the age of 35 they are far less likely to produce any children. Damage to sperm increases with age, reducing the likelihood of successful fertilisation and of full pregnancy, researchers say. And if a child is born to an older father, its chances of having a defect are also greatly increased.
This could be worrying news because the number of men over 40 becoming fathers has grown by 50 per cent in the past five years - and in 1999, 1 in 10 children born had a father over the age of 40.
So is it really true that sperm grows senile? And what can we do about it?
There is a large body of evidence that sperm effectiveness diminishes with age, but the subject still remains hugely under-researched. One man who has been working on the subject for a number of years is Dr Chris Ford, a senior research fellow at St Michael's Hospital, in Bristol.
Dr Ford doesn't like the media tag of male biological clock. "Men don't have a biological clock as such. There is no dramatic change, but there is lots of evidence that their fertility declines with age. It is not an undisputed fact at the moment, though."
Not undisputed, but increasingly obvious. Dr Ford's studies two years ago showed that the chance of conceiving within six months of trying falls by 2 per cent for every year the man is over 24. He points out that his conclusion was criticised because it did not fully take into account the age of the female partner in his study, but he wasn't surprised by the Seattle findings, cautiously calling them "feasible".
But that's not all
On top of this, another report published this month showed that genetic mutations in sperm increase with a man's age. This time, the study attempted to find out why a rare genetic disease - Apert syndrome - was more common in children born to older fathers.
Incredibly, US researchers at the McKusick-Nathans Institute for Genetic Medicine in Baltimore agreed with the Seattle report, again pinpointing the age at which men's fertility begins to decline as 35. From that age, it is said, the likelihood of disorders in offspring increases "rapidly".
"It makes sense that the mutations causing these diseases would occur more frequently in older men, and indeed that's what we saw for Apert syndrome," said director Ethylin Jabs.
So why are sperm more damaged with age? It appears to be down to a process called apoptasis. It's not a case of the body, or in this case the testes, going wrong - it's more to do with the fact that a careful balance is lost.
The researcher in charge of the Seattle report, Dr Narenda Singh, explained that sperm cells are frequently produced damaged or unhealthy, no matter what a man's age is. However, in young men these sperm are found, separated and destroyed in a process called apoptosis.
What happens in older men is that the process becomes less efficient and so greater numbers of imperfect sperm are present in semen. This then raises the chances of a faulty or mutated sperm getting to the egg first, and so makes miscarriage or foetal abnormality more likely.
There may still be hope, grandad
It is not just body processes that are at work, however. Dr Ford is joined by Professor Ian Craft of the London Fertility Centre and Dr William Keye, president of the American Society of Reproductive Medicine, in believing that lifestyle has an equally important role in male fertility.
There is strong evidence that smoking damages sperm, partly through reducing oxygen to the testicles and partly through the toxicity of smoke taken into the body. A healthy lifestyle reduces the general ingestion of toxins and therefore is also thought to improve sperm quality.
Dr Ford's latest research - to be published soon in the International Journal of Andrology - shows that what job a man does can also affect his fertility levels. The paper concludes that people in the printing industry take much longer to conceive, and the most logical explanation is that they breathe in significantly higher concentrations of toxic chemicals.
So is that it? If you are a 40-year-old, chain-smoking printer you might as well give up on having kids now? No. All the studies highlight how long it takes to conceive - not that it doesn't happen at all. It certainly appears that older men will take longer to father a child on average than younger men, but this is not the same as saying men have a biological clock.
The main concern is that, like women, as men grow older they have an increased chance of producing a child with some form of defect or abnormality. The chance is still small, however, and with fertilisation technology racing ahead faster than many are comfortable with, the chance of this is likely to grow smaller each year.
British Fertility Society
London Fertility Centre