Women aren't the only ones who have more fertility problems as they get older -- a new animal study suggests that time can take its toll on men's fertility, too.
That's because the quality of sperm -- not just sperm count -- can decrease throughout the years, researchers from the Colorado Center for Reproductive Medicine said.
"This is not a study observing male factor infertility. Rather, this is a study about once fertile males becoming infertile because of age," study researcher Mandy Katz-Jaffe, PhD, scientific director of the National Foundation for Fertility Research, said in a statement. "We were able to document when sperm from older males begins to suffer quality problems, and to understand the impact of older sperm on reproductive outcome."
Researchers found that when mice reached the equivalent of 40 human years, just half of the mice (who were fully fertile when they were younger) were able to naturally impregnate a female mouse. And when the mouse reached the equivalent of 50 human years, only 10 percent of mice were able to successfully impregnate a female mouse.
"Everything about the performance of the sperm was less after midlife, suggesting we should be thinking about the age of our couples, not just the age of the female," study researcher Dr. William Schoolcraft, medical director of the Colorado Center for Reproductive Medicine, told the Chicago Tribune. "The issue is sperm quality, not sperm count."
Mice's fertility is very comparative to humans' fertility, researchers said -- however, more studies are needed to see if the effect is the exact same in humans.
This is certainly not the first study to examine whether a man's age can impact his fertility. Another study, presented just this week at the annual meeting of the American Society for Reproductive Medicine, shows that between ages 41 and 45, the chances a man can get a woman pregnant drops by 7 percent each year, the Telegraph reported. That research was based on an analysis of 570 in vitro fertilization treatments that occurred between 2008 and this year.
The New York Times reported on research that shows that for some men, fertility drops with older age, while for other men, older age increases the risk of conditions like autism and schizophrenia in their offspring.
The New York Times reported:
It's a touchy subject. ''Advanced maternal age'' is formally defined: women who are 35 or older when they deliver their baby may have ''A.M.A.'' stamped on their medical files to call attention to the higher risks they face. But the concept of ''advanced paternal age'' is murky. Many experts are skeptical about the latest findings, and doctors appear to be in no rush to set age guidelines or safety perimeters for would-be fathers, content instead to issue vague sooner-rather-than-later warnings.
Psychology Today reported that the coupling of a maternal age over 35 AND a high paternal age could negatively impact fertility more than a maternal age lower than 35 and a high paternal age.