for National Geographic News
Note to men: You've got a biological clock too, and it's ticking.
It's not just women who face decreased reproductive success with age. The genetic quality of sperm deteriorates as men get older, according to a new study.
Starting in their 20s, men face steadily increasing chances of infertility, fathering an unsuccessful pregnancy, and passing on to their children a genetic mutation that causes dwarfism, according to the study.
The finding comes as more and more men are delaying fatherhood. Since 1980 U.S. birth rates have increased up to 40 percent for men aged 35 to 49 and decreased up to 20 percent for men under the age of 30, according to the research.
Studies have also shown that it takes longer for older men to conceive.
"We [now] know the probability for certain types of DNA damage goes up with age, and we can give you a mathematical probability," said Andrew Wyrobek, a researcher at the Lawrence Livermore National Laboratory in Livermore, California.
The higher the percentage of a man's sperm that has DNA damage, the less likely he will be able to successfully father a healthy child, Wyrobek added.
(See our quick overview of human genetics.)
Wyrobek is a co-lead author of the new study, which appears in today's issue of the journal Proceedings of the National Academy of Sciences.
Researchers have long known that female fertility decreases with age. The longer women delay reproduction, the greater their risk of miscarriage and giving birth to children with diseases such as Down syndrome.
Female fertility abruptly ends with the onset of menopause.
"Our research suggests that men too have a biological time clock, only it is different," Brenda Eskenzai, a study co-author at the University of California, Berkeley's School of Public Health, said in a statement.
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