Older fathers may face higher risks than previously thought for having children with psychiatric problems, including bipolar disorder, autism and attention deficits, according to 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 who fathered children after age 24 faced increasing odds for having children with psychiatric problems or academic difficulties, with the greatest risks seen at age 45 and older.
The results add to evidence challenging the notion that men's sperm are timeless, but this kind of research is not proof. And by no means are children of older fathers certain to have problems. Absolute risks were small: fewer than 1 per cent of children of older fathers had autism, attention deficit hyperactivity disorder (ADHD) or bipolar disorder; and fewer than 4 per cent had schizophrenia or fell victim to substance abuse or attempted suicide. 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 in the United States.
Compared with children of the youngest fathers, those fathered by men at age 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.
Molecular geneticist Simon Gregory, an associate professor at Duke University in the US, called the 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. Still, Gregory said there was "no reason to ring the alarm bells that older men shouldn't have kids" unless the results were replicated in additional research and molecular evidence was found.
D'Onofrio said the researchers took into account several factors that could have influenced the results, including the mothers' age at conception, parents' education and history of psychiatric problems, and siblings' health.
"People frequently ask me, 'What's the safe age"' to father children, but the answer is not clear-cut, D'Onofrio said. "There is no threshold where on one side it's safe and on the other side it's problematic."
He thinks the reason risks may increase with age is that sperm are continually produced throughout men's lives and mutations may occur each time cells divide to create new sperm. The study was published online on Wednesday by JAMA Psychiatry.