Older fathers may face higher risks than previously thought for having children with psychiatric problems, including bipolar disorder, autism and attention deficit.
In the largest study to examine the potential links, American and Swedish researchers examined data on more than 2.6 million Swedes born from 1973 to 2001. Men over 24 who fathered children faced increasing odds for having children with psychiatric problems or academic difficulties, with the greatest risks seen among those 45 and older.
The results add to evidence challenging the notion that sperm are timeless, but this kind of research is not proof and children of older fathers are by no means certain to have problems.
Absolute risks were small – less than one per cent of children of older fathers had autism, attention deficit-hyperactivity disorder or bipolar disorder; and less than four per cent had schizophrenia or fell victim to substance abuse or attempted suicide.
There’s no reason to ring the alarm bells that older men should not have children unless the results are replicated in additional research and molecular evidenceis found
Academic difficulties were more common but still did not affect most children of older fathers.
Even so, the magnitude of increased risks faced by children born to fathers aged 45 and older versus fathers aged 20 to 24 was surprising, said lead author Brian D’Onofrio, an associate professor in the psychological and brain sciences department at Indiana University.
Compared with children of the youngest fathers, those fathered by men 45 and older faced risks almost 25 times greater for bipolar disorder; 13 times greater for ADHD; more than three times greater for autism; almost three times greater for suicide attempts; and about two times greater for schizophrenia and substance abuse.
The study was published online in JAMA Psychiatry.
Molecular geneticist Simon Gregory, an associate professor at Duke University, called the new study impressive because of its size and depth – the authors had access to a registry of most births in Sweden over more than 20 years, along with reams of data on psychiatric treatment, education and social welfare.
But he said “there’s no reason to ring the alarm bells” that older men should not have children unless the results are replicated in additional research and molecular evidence is found.
D’Onofrio said the researchers took into account several factors that could have influenced the results, including the mother’s age at conception, parents’ education and history of psychiatric problems, and siblings’ health, and still found strong risks linked with older men.
“People frequently ask me ‘What’s the safe age to father children?’ but the answer is not clear-cut,” he said. “There is no threshold where on one side it’s safe and, on the other side, it’s problematic.”
He is among scientists who think the reason risks may increase with advancing age is that sperm are continually produced throughout men’s lives and mutations may occur each time cells divide to create new sperm.
By contrast, women are born with a set number of eggs that become susceptible to certain genetic mutations, including those that cause Down’s syndrome, as women age. Other research has suggested women’s age might play a role in autism and other disorders, but fathers’ advanced age was not considered a potential risk until fairly recently.
Christopher Pittenger, a Yale University expert in psychiatric disorders, called the results convincing and said it was likely that many genetic mutations linked with older age contributed to the conditions studied, but that other factors also played a role.