Children born to older fathers might be at higher risks for a variety of psychiatric problems and academic difficulties compared with children born to younger fathers, a new study said Wednesday.

Researchers from U.S.-based Indiana University studied people born in Sweden from 1973 to 2001 in collaboration with their colleagues from Karolinska Institute in Stockholm, capital of Sweden.

The researchers estimated the risk of psychiatric problems, including autism, attention-deficit/hyperactivity disorder (ADHD), psychosis, bipolar disorder, suicide attempt and substance abuse, as well as academic trouble like failing grades, low educational attainment and low IQ scores, used siblings, cousins and first- born cousins in comparison.

Compared to a child born to a 24-year-old father, a child born to a 45-year-old father is 3.5 times more likely to have autism, 13 times more likely to have ADHD, two times more likely to have a psychotic disorder, 25 times more likely to have bipolar disorder and 2.5 times more likely to have suicidal behavior or a substance abuse problem, the researchers said.

For most of these problems, the likelihood of the disorder increased steadily with advancing paternal age, suggesting there is no particular paternal age at childbearing that suddenly becomes problematic.

"We were shocked by the findings," said Brian D'Onofrio, lead author and associate professor of the Indiana University. "The specific associations with paternal age were much, much larger than in previous studies."

Previous research suggested sperm of older men have more genetic mutations, which may cause an increased risk of child psychiatric, intellectual and academic problems.

D'Onofrio said their study may have important social and public policy implications.

"The findings suggest that APA (advancing paternal age) represents a risk of numerous public health and societal problems. Regardless of whether these results should lead to policy changes, clarification of the associations with APA would inform future basic neuroscience research, medical practice and personal decision-making about childbearing," they wrote in their paper published in the U.S. journal JAMA Psychiatry.