Children of older fathers have lower IQ scores, study shows

Children of older fathers scored lower than offspring of younger fathers on IQ tests and a range of other cognitive measures at 8 months old, 4 years old and 7 years old, according to a study that adds to a growing body of evidence suggesting risks to postponing fatherhood.

The study, released Monday, is the first to show that children of older fathers do not perform as well on cognitive tests at young ages. Although the differences in scores were slight and usually off by a few points on average, authors of the report called the findings "unexpectedly startling."

"The older the dads were, the slightly worse the children were doing," said Dr. John McGrath, the paper's senior author and a professor of psychiatry at the Queensland Brain Institute in Brisbane, Australia. "The findings fit in a straight line, suggesting there may be some steady beat of mutations happening in the dad's sperm."

Earlier studies have found a higher incidence of schizophrenia and autism among offspring of men who were in their mid-40s or older when they had children. A 2005 study showed that 16- and 17-year-olds with older fathers scored lower on nonverbal IQ tests, as did offspring of teenage fathers.

The new study, published in the online journal PLoS Medicine, reanalyzed data from the federally sponsored Collaborative Perinatal Project, which gathered data from more than 50,000 pregnant women seen at 12 university clinics from 1959 to 1965.

Researchers analyzed the scores of 33,437 children who, as part of the project, had been tested at regular intervals in a variety of cognitive skills, including thinking and reasoning, concentration, memory, understanding, speaking and reading, as well as motor skills. Fathers in the study were age 14 to 66, while mothers were 12 to 48.

Regardless of the mothers' ages, children whose fathers were at least 50 had lower scores on all tests, except those assessing physical coordination, than those whose fathers were 20, researchers found. And the older the fathers, the more likely the children were to have lower scores, they found.

By contrast, children with older mothers generally performed higher on the cognitive measures, a finding in line with most other studies, suggesting that these children may benefit from the more nurturing home environments associated with the generally higher income and education levels of older mothers, researchers said.

"I think there has been a bit of a cultural bias against even looking at this issue, but finally people are willing to entertain this," said Dr. Dolores Malaspina, a New York University Medical Center psychiatry professor who has written studies on the risk of schizophrenia among children of older fathers as well as the lower nonverbal IQ scores found among teenagers with older fathers.

"It turns out the optimal age for being a mother is the same as the optimal age for being a father," Malaspina said. "The fact that men can stay fertile longer is a different issue."