Monday, August 24, 2009

Best before (34)

Best before
Posted 12 hours ago
Do men have a best-before date when it comes to fathering kids? Ridiculous, most of us would answer. Just look at these celebrity old guys who became dads in their 50's, 60's, and beyond: Charlie Chaplin at 73; former Prime Minister Pierre Trudeau at 72, Pablo Picasso at 68; Larry King at 65; Warren Beatty at 63; and Dave Letterman at 56.
"Women are born with a fixed number of oocytes," says Dr. Bernard Robaire, describing the female germ cells crucial to reproduction. The McGill University researcher who is funded by the Canadian Institutes of Health Research or CIHR, says that men have no such limitation. Unlike women who, after the age of 35 find it more difficult to get pregnant, men produce 1,000 sperm a heartbeat - about 100 million sperm each day.
Theoretically speaking, then, men can go forth and multiply forever - or as long as their hearts beat. "The argument has always been that because men keep producing sperm that are fresh all the time it makes no difference whether you have sperm from an 85 year old man or a 35 year old man," says Robaire.
However, there's a growing body of research that suggests there may be limits to men's fertility, too. Recent studies have shown that men over the age of 40 have a lower chance of producing children than their younger counterparts. And they have an elevated risk of having children with autism, bipolar disease and schizophrenia.
In addition to concerns about mental illness, some studies have also shown that children born to older fathers score lower on intelligence tests. One study found that the incidence of down syndrome was related to sperm approximately 50% of the time.
"What we found was that if you put old males with young females the development of the embryos was different," says Robaire, explaining his work with lab rats. "We found a change in the weight of the embryos, but what was most striking was an increase in the post-natal death right after birth. Development was not normal.
"It seems that, as men age, the quality of their sperm changes," he explains. "The sperm's swimming ability changes, and the quality of its DNA decreases." So even though men continue to produce fresh sperm, the quality suffers because the sperm, which come from aging stem cells in the testes, accumulate oxidative damage over time.
"Fertility doesn't decline - only the quality of the sperm," he stresses. So is there a biological clock for men? "Yes, because a biological clock doesn't just refer to the number of sperm produced but also their quality." Robaire adds that there are many older men who produce children who are normal in every way. Nonetheless, studies show that the best age for perfect sperm is under 40.
With older men increasingly fathering children, the issue of sperm quality needs to be heard, says Robaire. "All our worries are about women having kids over the age of 35. But a man's sperm quality decreases with age and so therefore do the chances of his children being normal."

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