Men May Have Biological Clocks, Too
Some researchers say a man's age may affect not only his ability to father a child -- but the health of his offspring.
Lifestyle: Another Break in the Sperm Chain
While the aging sperm machine may be one theory, McCulloh says there is an equally strong possibility that it may not be the aging process at all that's at fault, but rather what a man does over his lifetime that matters most.
"It is very difficult to separate the effects of natural aging from environmental effects like smoking, drinking, drug use, and radiation exposure. There are a whole battery of environmental assaults that may accumulate over time, causing at least some of the reproductive issues we now attempt to link solely to age," says McCulloh.
Silverman agrees, suggesting that much the way lifestyle practices affect the health of other systems in the body, such as the heart, so too might they affect male reproduction. "The longer a man lives, the more exposure he has -- which might make a difference," says Silverman.
At least one study indicated that oxidative damage -- one type of environmental assault -- can increase chromosomal damage in sperm.
In animal research published in 2005 in the journal Fertility and Sterility, researchers found that not only was the DNA of sperm susceptible to oxidative damage, but the older the male, the more susceptible the sperm was to developing breaks in the DNA.
It is this kind of genetic upset that experts say could be behind some of the birth defects and other problems that until recently were thought to be exclusively related to the mother.
The American Society of Reproductive Medicine now recommends that sperm donors be men that are "ideally less than 40 years of age to minimize the potential hazards of aging."
What Men Can Do
While evidence seems clear that at least the possibility of a male biological clock exists, not everyone believes it comes with a fertility alarm. Indeed, some experts cling steadfastly to the notion of omnipotent and virtually indestructible sperm at any age.
"I'm not at all convinced [age is a factor]. These are not prospective studies and you cannot pick the disease state and then work backwards. You can't do it that way because you're going to come up with the wrong conclusion. You may have the observation, but you don't have the link," asserts Andrew McCullough, MD, director of sexual health and male infertility at NYU Medical Center in New York City.