A new study links the age of fathers to the likelihood of mental illness in their biological children.
Researchers from Indiana University and Sweden tracked all the people born in Sweden between 1973 and 2001 — a sample size of more than 2.6 million individuals. (Via The JAMA Network)
The study compared siblings — those born when their fathers were between 20 and 24 years old, and those born when their fathers were 45 or older.
The younger siblings — born when their fathers were 45 or older — were 24 times more likely to have bipolar disorder, 13 times more likely to have attention deficit hyperactivity disorder and more than three times more likely to have autism.
Younger siblings were also more likely to have psychosis, attempt suicide or develop substance abuse problems. Being born later also increased the probability they'd fail a grade or not progress through school.
The study's lead author said the associations were surprisingly strong, but told NBC there are a variety of factors at play here.
"This study shows that there’s a correlation between a father's age at childbearing and the children's psychiatric problems," Dr. Brian D'Onofrio said. "But this does not prove that advancing age causes those problems." (Via NBC)
The researchers believe the higher incidence of mental illness could be a result of genetic mutations.
Experts suspect that as men age, they're exposed to more environmental toxins, which might lead to DNA mutations in their sperm. (Via KNTV)
And as one epidemiologist told the Telegraph, the Indiana researchers didn't design the study to account for those potential outside factors.
"We don't know the relationship between father and children in this study, and for issues like suicide and substance abuse that is likely to have the biggest impact," Dr. Mark Pearce said. (Via The Telegraph)
But in discussing the study with The New York Times, a genetics professor at the University of North Carolina pointed out, "The last thing people should do is read this and say, 'Oh no, I had a kid at 43, the kid’s doomed.' The vast majority of kids born to older dads will be just fine."