SATURDAY, Feb. 14, 2009 (HealthDay News) -- It wasn't all that long ago that any suggestion that a man had a "biological clock" like a woman, and should father children sooner rather than later, would have been given short scientific shrift.
Not anymore. Today, a growing body of evidence suggests that as men get older, fertility can and does decline, while the chances of fathering a child with serious birth defects and medical problems increase.
Some studies have linked higher rates of serious health problems such as autism and schizophrenia in children born to men as young as their mid-40s.
And doctors and researchers are busy trying to figure out how men who choose to delay fatherhood -- either by choice or necessity, such as a lack of a partner -- can offset the effects of their biological clocks as those clocks wind down.
Interestingly, problems with reduced fertility can start long before middle age, said Dr. Harry Fisch, one of the pioneers in the field in male fertility and director of the Columbia University College of Physicians and Surgeons' Male Reproductive Center, in New York City.
"We know after age 30, testosterone levels decline about 1 percent per year," said Fisch, author of the book The Male Biological Clock.
Research done at the University of Washington has found that "as men age, DNA damage occurs to their sperm," said Dr. Narendra P. Singh, a research associate professor in the department of bioengineering, who co-authored a study on the subject.
Several other studies point to problems in the offspring of older fathers, as well as older men experiencing fertility problems.
For instance, Fisch and his colleagues found that if a woman and a man were both older than age 35 at the time of conception, the father's age played a significant role in the prevalence of Down syndrome. And this effect was most detectable if the woman was 40 or older -- the incidence of Down syndrome was about 50 percent attributable to the sperm.
Other researchers have found that children born to fathers 45 or older are more likely to have poor social skills, and that children born to men 55 and older are more likely to have bipolar disorder than those born to men 20 to 24 years of age at the time of conception.
On other fronts, researchers at Mount Sinai School of Medicine in New York City found that children of men aged 40 or older were about six times more likely to have autism. Still another study found that the children of fathers who were 50 or older when they were born were almost three times more likely to be diagnosed with schizophrenia.
Fisch is now focusing much of his attention on encouraging men to assess if their biological clock is ticking faster than it should. For instance, men who are overweight or obese tend to have more fertility problems than healthier men.
"It turns out that if you are too heavy, you have a lower sperm count," he said, adding that excess body fat causes testosterone levels to decline. The good news: Losing weight helps them return to normal.
Singh advises older men who want to become fathers to pay attention to lifestyle issues and practice healthy habits that will, in turn, keep their sperm healthy. That particularly means no smoking and no overuse of alcohol, he said.
Both Fisch and Singh said they don't think there's a "cutoff" point for fatherhood. And they said it's difficult to pinpoint the "ideal" age to father a child, especially since many couples today are marrying later and delaying starting a family.
But Fisch did say, "The sooner, the better."
To learn more about male reproductive health, visit the American Urological Association Foundation.