By the time they reach their 20s, sons born to older fathers and those who were born to younger men score about the same on intelligence tests, a new Danish study finds.
Whatever negative biological effects a father's age might have on his child may be offset by the benefits of being raised by a better educated and financially stable older father, researchers said.
"Our results are reassuring for older fathers," Liselotte Petersen, the study's lead author, said in an email.
"Our finding is that any potentially deleterious effects of older fathers on general cognitive ability, as young adults may be counter-balanced," Petersen, an associate professor at Aarhus University in Denmark, said.
Previous studies have suggested that the children of older fathers are more likely to be diagnosed with autism and schizophrenia. That led Petersen and her colleagues to suspect that the children of older fathers may also have lower intelligence scores.
For the study, they used data collected from 169,009 men born after 1955. The goal was to see if there were any differences in intelligence related to how old their fathers were at the time of their birth.
The researchers used the participants' scores from the intelligence test that's required for military service in Denmark. Each participant took the test when he was about 20 years old.
The participants' average score was 42, which is about the same as that of the general Danish population.
Initially, it appeared that the children born to teenagers or to fathers over age 35 scored lower on the intelligence test, compared to the kids of fathers in their mid to late 20s.
But the difference disappeared when Petersen and her colleagues adjusted those scores to account for the parents' education levels, the children's birth order, the mother's age and the year the test was administered.
Children of teenage fathers, however, scored on average about one point lower, compared to the kids of fathers aged 25 to 29.
Small changes in intelligence may impact people in subtle ways, the researchers write in PLOS ONE. But that difference would be magnified if it were applied across the entire population.
The new study, however, can't prove that a father's age will directly impact his child's intelligence.
Also, it's hard to compare the intelligence scores used in this study to scores in previous research, according to NYU Langone Medical Center's Dr. Dolores Malaspina, because the intelligence test used is unique to Denmark.
But, Malaspina, who has done similar work but wasn't involved in the new study, wrote in an email that this is a "compelling area of research."