WebMD Medical News
Louise Chang, MD
March 9, 2009 -- Children born to older fathers don't perform as well on
tests of thinking skills during infancy and early childhood, while those born
to older mothers have higher scores on the same tests, a study shows.
This latest study follows previous research showing a link between older
fathers and health problems such as birth defects, autism, and schizophrenia,
suggesting that the "biological clock" isn't just a concern of
"The links emerged in the 1990s that the offspring of older fathers had
an increased risk of schizophrenia, [and] since then data has accumulated also
linking paternal age to autism and more recently bipolar disorder," says
study researcher John McGrath, MD, PhD, a professor at the Queensland Brain
Institute of the University of Queensland, Brisbane, Australia.
"We wondered if it was a more generic process," he says, and that
triggered their current research to look at potential links between a father's
age and child development, including IQ.
The study is published this week in PLoS Medicine.
McGrath's team analyzed data from a large study called the U.S.
Collaborative Perinatal Project, which recruited pregnant women from 12 sites
in the U.S. from 1959 to 1965. The data from this ongoing project has been a
"treasure trove" for researchers, McGrath says.
His team looked at more than 33,000 children born between 1959 and 1965 and
then looked at their results on cognitive tests administered at ages 8 months,
4 years, and 7 years. The tests evaluated the children's ability to think and
reason, measuring such skills as concentration, learning, speaking, reading,
arithmetic, memory, and motor skills such as coordination.
Finally, they looked for links with the father's age, the mother's age, and
in one analysis also adjusted for socioeconomic factors such as family income
and parental education.
The average age of the fathers in the study was 28.4 and ranged from 14 to
66. The mother's average age was 24.8 and ranged from 12 to 48.
In recent years, according to the paper, it has become very common for
couples to delay having children until their late 30s.
The older the father, the more likely the child was to score lower on the
tests, except for one measure of motor skills.
When they looked at the mother's age, however, they found that the older the
mother, the higher the children scored on the thinking skills tests. (That
finding, reported in earlier studies as well, may be due to a more nurturing
home environment if the mother is older, but this study suggests children of
older fathers don’t reap the same benefit.)
However, when the researchers adjusted for such factors as the parents'
socioeconomic status, including income and education, it modified the effect of
both parents' ages on the intelligence tests. For instance, the average score
on the Stanford Binet Intelligence Scale was nearly 6 points lower for children
born to fathers age 50 compared to those born to fathers age 20. But when the
socioeconomic factors were taken into account, the difference dropped to 2.2
While the study findings may suggest the best combination of parents is an
older woman with a younger man, McGrath says it's too early to make any
"For the moment, our study suggests that paternal age, like maternal
age, also should be 'on the radar screen'" for researchers, he says. As
research accumulates, he says, "we can put this knowledge into the public
health equation," weighing it along with many other factors before
What's behind the link between older fathers and lower IQ? "There is a
growing body of evidence suggesting that the sperm of older dads develop more
mutations, that is, spelling mistakes in the DNA code," McGrath says. His
team is researching this idea further in animal studies comparing young mice
with older ones.
Still, it's important to put the paternal age in perspective, McGrath says.
"The significance of the effect linking paternal age and child cognition is
small compared to many other socio-cultural factors -- for example good
prenatal nutrition, good nutrition for the offspring, good education, nurturing
home life, excellent teaching and school opportunities [and so on]."
"We have known about the paternal age effect for many years," says
Harry Fisch, MD, director of the Male Reproductive Center and director of
urologic microsurgery at Columbia University Medical Center of New York
Presbyterian Hospital. Yet, he says, "We are just starting to scratch the
Testosterone levels begin to decline slowly at age 30, Fisch says. Ideally,
men should father children "sooner rather than later," he says.
"The 20s and early 30s are ideal, but real life intervenes," he
says, making that time frame not feasible due to lack of a partner, difficulty
getting pregnant, financial restraints, or a host of other factors.
In a perspective on the study, published in the same issue of PLoS
Medicine, Mary Cannon, MD, of the Royal College of Surgeons in Dublin,
Ireland, says it is important to take socioeconomic factors into account when
looking at the effect of a father's age (as well as a mother's).
She points out that taking into account the socioeconomic factors is not a
precise science, and that if researchers could truly adjust for every relevant
socioeconomic variable, the effect of the father's age on the child's
intelligence might be wiped out completely. She, too, calls for more
SOURCES:John McGrath, MD, PhD, professor, Queensland Brain Institute, University of
Queensland, Brisbane, Australia.Harry Fisch, MD, director, Male Reproductive Center; director of urologic
microsurgery, Columbia University Medical Center, New York Presbyterian
Hospital.Saha, S. PLoS Medicine, vol 6; online March 2009.Cannon, M. PLoS Medicine, vol 6; online March 2009.
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