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Older Fathers, Lower IQ in Kids?

Study Shows Children of Older Dads Had Lower Performance on Intelligence Tests
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Intelligence Tests for Children of Older Fathers

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 points.

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 specific recommendations.

"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 dispensing advice.

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]."

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