CHICAGO — 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 1973-2001. Men who fathered kids after age 24 faced increasing odds for having children with psychiatric or academic difficulties, with the greatest risks seen at age 45 and up.

The results add to evidence challenging the notion that men’s sperm are timeless, but this kind of research isn’t proof. And by no means are children of older dads certain to have problems. Absolute risks were small – less than 1 percent of kids of older dads had autism, attention deficit-hyperactivity disorder or bipolar disorder; and less than 4 percent had schizophrenia or fell victim to substance abuse or attempted suicide.

Academic difficulties were more common but still didn’t affect most kids of older dads.

Even so, the magnitude of increased risks faced by kids born to dads aged 45 and older versus dads aged 20 to 24 was surprising, said lead author Brian D’Onofrio, an associate professor in brain sciences at Indiana University.

Compared with kids of the youngest dads, 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.

The study was published online in JAMA Psychiatry.