Children of older fathers have lower intelligence scores than those born to younger men, perhaps because of cumulative damage to men’s sperm during their lives, Australian and U.S. researchers found.
Children born to fathers who were age 20 scored an average of 2 points higher on an IQ test than children born to 50-year-old fathers, according to the study of data collected on 33,437 children from 1959 through 1965.
Average IQ among children dropped steadily on a number of tests as their fathers’ ages rose, according to the research published today in Public Library of Science, Medicine, an online journal.
More men and women are becoming parents at later ages, probably for career and financial reasons, said Mary Cannon, a psychiatrist at the Royal College of Surgeons in Dublin who wasn’t involved in the analysis.
Children of older fathers have been shown previously to be at higher risk for some ailments. More research into the health effects of this trend is needed, she said in a commentary in the same journal.
“The body of evidence implicating paternal age as a risk factor for a range of adverse offspring outcomes should not be ignored,” Cannon said.
The study looked at intelligence test scores of children at ages 8 months, 4 years and 7 years. The children were the only offspring of their parents. Results were adjusted for factors that might affect their performance on tests, such as family income, said John McGrath, a psychiatrist at the University of Queensland in St. Lucia, Australia, who led the analysis.
The data confirmed earlier reports that children of older mothers perform better on intelligence tests, a finding that has been attributed to higher income and education among women who wait to have their first child.
That trend holds true even though children born to women age 40 and older are at increased risk for Down syndrome, a genetic disorder that affects the brain, heart and other organs, McGrath said.
