Dad's Age May Lower Junior's IQ

Older fathers may have less intelligent offspring.

March 9, 2009, 11:21 AM

March 9, 2009— -- Though the media have been abuzz in recent years over the phenomenon of cougars -- older women dating much younger men -- a new study hints that pairings of older mothers and younger fathers might be optimal for the children's IQs.

The study of more than 33,000 children in the United States looked at parental age and how it affected scores on intelligence tests at 8 months, 4 years and 7 years of age. While the children of older fathers scored slightly lower, the children of older mothers tended to perform slightly better.

"In general, you would predict that the offspring of older parents would do better, because the parents tend to have better socioeconomic position, stability, education, health literacy, etc.," said Dr. John McGrath, a psychiatrist and epidemiologist at the Queensland Brain Institute in Brisbane, Australia, and one of the study's authors.

"This is exactly what we see for the offspring of older mothers. This would probably be driven by understandable socio-cultural factors. Thus, the fact that we see the opposite pattern for fathers' age is startling."

The deficits of the children of older fathers -- whose sperm will degrade as it replicates over time, in contrast to eggs, which are formed early in a woman's development -- are worrisome, McGrath said, because of the trend of men waiting longer to have children.

That might even pose a problem to future generations.

"Over time, many societies are delaying parenthood," he said. "Worryingly, if the adverse health and educational outcomes we see are due to new mutations in dad's sperm cell, these will probably be transmitted to the next generation."

Given the size of the study, the small deficits found in the children of older fathers were still significant. But while other researchers called the findings interesting, they expressed skepticism at how well the findings would translate to today, because the sample of children in the study was taken between 1959 and 1965.

Older Dads' Involvement May Be Key in Kids' IQ

The finding, then, may be how an uninvolved father can impair a child's development.

"Fathers born during this time [1909 to 1915, based on the years of the study] were fairly uninvolved in parenting and certainly more so with age," said Melanie Killen, a professor of human development at the University of Maryland. "Thus, fathers were not providing important cognitive stimulation for children through play and social interaction that is highly related to performance on the [intelligence tests]."

Killen said that age means something different now, as well.

"Being 50 in 1960 means something very different from being 50 today, particularly in terms of early nutrition and development," she said. "It doesn't surprise me that children born in the 1960s with 'older' dads may have missed important opportunities for cognitive developmental engagement and stimulation."

She added that older mothers may have been better positioned to help make up those gaps.

"Older mothers, however, would be significantly related to more advanced cognitive development given that they would have more maturity to handle the more developmentally important cognitive stimulation roles that a 'single' parent plays, given the expectations of parenting during this time."

Dr. Susan Klugman, a prenatal geneticist at Mount Sinai School of Medicine in New York City, said that the study should be replicated with children born now. She noted that one complication might be that people smoked more when the data were taken, and that might have resulted in an increase in defects in the sperm.

A potential problem with reading too much into the study, noted Alan E. Kazdin, a professor of psychology and child psychiatry at Yale, is that it only followed children through the age of 7.

Because of that, he noted, some of the findings may not show what happens to these children throughout their lives.

"Older parents sometimes provide more compensatory advantages [if their financial means are better] and experiences, and that these findings, while important, did not show that the results had any practical consequences in childhood or adulthood."

One Less Worry for Older Moms?

Perhaps the most important result from the study, noted Mark Reinecke, chair of psychology for child development at the Northwestern University School of Medicine, is that it might alleviate the fears of older women considering having children.

To them, he said, "the findings are reassuring. A great deal has been written about the risks of having children after 40 years of age. These findings allay these concerns, at least a bit."

Reinecke noted that other factors would play a greater role in the child's ultimate success.

"Beyond this, I would emphasize the importance of maintaining a nurturing, secure, predictable, and intellectually stimulating home environment. ... That's the key during the early years," he said.

But the benefits that come with age do have a tradeoff, noted Dr. John Constantino, a child and adolescent psychiatrist at the Washington University School of Medicine in St. Louis.

"There is a point at which maternal emotional maturity gets overshadowed by increased risk of birth defects in offspring," he said.

McGrath cautioned that while his study's findings need closer scrutiny, it is too soon to make any recommendations based on it.

"I am sure your viewers and readers will want some type of guidance," he told, "but, it is too early to make any recommendations. Research needs to be replicated and confirmed in different settings, etc. For the moment, our study suggests that paternal age, like maternal age, also should be 'on the radar screen' for the research community."

"As the research evidence builds, then we can put this knowledge into the public health equation. ... Our small study is one part of the jigsaw."

Michelle Schlief of ABC News contributed to this report.