Men have long been fathering children well into old age. Tony Randall entered daddyhood at age 77. Charlie Chaplin became a proud pop for the last time at age 73. Rod Stewart had his seventh child at 60 — and may still be on a roll.
But while it seems that older men and fatherhood are no odd couple, scientists have begun questioning the assumption that the biological clock is only a concern for women.
Unlike women, who have a marked decline in fertility in their 30s, men’s biological clocks appear to wind down gradually and progressively over the course of their lives. One study, for instance, found that sperm motility — their ability to be strong swimmers capable of reaching and fertilizing an egg — decreased by a steady 0.7 percent per year for men between the ages of 22 and 80.
Sperm counts appear to decline with age, too. But even men with reduced counts still may be able to father children since it takes just one sperm.
Sperm from older men also may be more likely to contribute to health problems in children. Recent studies have linked older fatherhood with increased risks of schizophrenia, autism, Down syndrome and other disorders in children. And in this case, “older” means as young as 40.
“Young people who want to have a family may want to start considering the age of the father as much as the mother,” says Dr. Dolores Malaspina, a fertility researcher and chair of the psychiatry department at New York University School of Medicine.
In 2001, Malaspina published a study showing that the chance of a child developing schizophrenia rose in concert with the father’s age. The risk was one in 141 for children of fathers under 25, and one in 47 for those with fathers 50 and older. Other studies have replicated those results. Researchers estimate as many as one in four cases of schizophrenia may be linked with a father’s age.
In another study, Malaspina linked paternal age with a greater chance of autism-related disorders — more than a fivefold increased risk for kids born to fathers 40 or older, compared with those born to dads younger than 30.
Since 1980, birth rates have increased 40 percent for fathers ages 35 to 49, while births involving men under 30 have declined. And Malaspina theorizes the rise in fathers’ ages may explain some of the upswing in autism diagnoses, though this hasn’t been proven.
The culprit behind a man’s ticking biological clock may be the so-called “copy error theory.” Imagine that you copied a document on a Xerox machine. And then you made a copy of the copy. And then a copy of the copy of the copy. With each new generation, the risk of blurs and imperfections increases. The same sort of thing happens with sperm. While women are born with all the eggs they’ll ever have, men constantly produce new sperm by replicating the previous generations of sperm, thus increasing the chance of mutation with each duplication.
Last year, Dr. Andrew Wyrobek, a medical biophysicist at Lawrence Berkeley National Laboratories in Berkeley, Calif., published a study that examined the sperm of 97 healthy men. Breaks in sperm DNA strands, called DNA fragmentation, rose steadily from ages 20 to 80. These breaks can cause fertility problems, pregnancy failures and an increase in some genetic diseases. For instance, genetic mutations in the sperm that can cause dwarfism, a disorder that affects bone growth, increase about 2 percent each year.
“Sperm cells, with the DNA tightly compacted in the sperm head, are one of the few cells in the body that don’t have the ability to repair themselves,” Wyrobek points out.
Exactly what this all means is hazy, as even Wyrobek readily acknowledges. Even if sperm levels decline with age, some men can father children into advanced years — an Australian mine worker made headlines in 1992 by becoming a father at 93 years, 10 months. And though the risk of genetic defects might increase with the father’s age, those risks remain relatively small and can vary from person to person.
What’s more, Dr. Rebecca Z. Sokol, president of the Society for Male Reproduction and Urology and a professor of clinical obstetrics and gynecology at the University of Southern California, says the studies linking a father’s age to abnormalities in sperm DNA and genetic defects are based on “very soft, preliminary data.” Some of the studies, she notes, didn’t control for factors such as alcohol use, which may influence the results.
A sperm shape-up plan
Given all this, making recommendations is dicey. Dr. Harry Fisch, director of the Male Reproductive Center at Columbia University Medical Center of New York-Presbyterian Hospital and the author of “The Male Biological Clock,” suggests middle-aged men who plan to become fathers should try to get their sperm in top form.
“If you want to run a marathon, you have to get in shape for it,” Fisch says. “In the same way, you have to train to have a baby.”
Mostly, the recommendations involve sound health practices that are beneficial at any age: quit smoking, avoid excess booze and empty calories, and shed extra pounds since obesity is related to male infertility.
Another tip: avoid hot tubs. Men’s testicles are outside the body in the scrotum to keep the sperm cooler than the core body temperature, and daily exposure to high levels of heat can cause a reversible decrease in sperm quality.
Fisch also advises older, aspiring fathers go in for a physical examination. Doctors can check for conditions such as varicoceles, dilated veins in the scrotum similar to varicose veins in the legs, which can obstruct sperm. Varicoceles, present in about 40 percent of infertile men, can be corrected with outpatient surgery.
Though more research is needed, Malaspina says it’s possible that — just like women — the prime time for becoming a dad is one's 20s and early 30s.
“Men," she says, "your biological clocks are ticking, too.”
Joe Mullich is a freelance writer in Sherman Oaks, Calif., who has written for Health, Men's Health and Salon.