Lower I.Q. Scores Among Children of Older Fathers
By RONI CARYN RABIN
Published: March 9, 2009
Children of older fathers scored lower than offspring of younger dads on I.Q. tests and a range of other cognitive measures at eight months, four years and seven years of age, according to a new study that adds to a growing body of evidence suggesting there are risks to postponing fatherhood.
The study is the first to show that children of older fathers don’t perform as well on cognitive tests at very young ages. Although the differences in scores were slight and usually just off by a few points on average, researchers called the findings “unexpectedly startling."
“The older the dads were, the slightly worse the children were doing,” said Dr. John J. 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- to late 40s or older when they had children. A study published in 2005 reported that 16- and 17-year-olds with older fathers scored lower on non-verbal I.Q. tests, as did the offspring of teenage fathers.
The new study, published on Monday in the journal PLoS Medicine, re-analyzed data from the Collaborative Perinatal Project, which gathered information from pregnant women seen at 12 university clinics in the United States between 1959 and 1965.
The researchers analyzed the scores of 33,437 babies resulting from these pregnancies. They had been tested at regular intervals on a variety of measurements of cognitive skills, including thinking and reasoning, concentration, memory, understanding, speaking and reading, as well as on motor skills.
Regardless of their mothers’ ages, children whose fathers were 50 years old had lower scores on all of the measures, except for those assessing physical coordination, than those whose fathers were 20, the 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 that is in line with most other studies, suggesting these children may benefit from 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, professor of psychiatry at New York University Medical Center, who authored the studies finding an increased risk for schizophrenia among children of older fathers, as well as studies that found lower non-verbal I.Q. scores among teens with older dads.
“It turns out the optimal age for being a mother is the same as the optimal age for being a father. The fact that men can stay fertile longer is a different issue."