The children of older fathers may be up to 25 times more likely to develop bipolar disorder and 13 times more likely to develop autism, a new study indicates.

The research, which was carried out by US and Swedish scientists, found that children appear to have an increased risk of experiencing a range of psychiatric and academic problems if their fathers are older at the time of their conception.

They noted that in recent years, the average age that people have decided to have children has been increasing and the implications for this are still unclear.

And research in this area has tended to focus on the age of the mother. As a result, they decided to investigate more closely the potential effect of paternal age on the health of children.

They examined data relating to every child born in Sweden between 1973 and 2001 and found a major association between paternal age at the time of conception and a number of educational problems and mental health disorders, including bipolar disorder, ADHD (attention deficit hyperactivity disorder) and a low IQ.

The study found, for example, that a child born to a 45-year-old father is at least three times more likely to have autism, 13 times more likely to have ADHD and 25 times more likely to have bipolar disorder, compared to a child born to a 24-year-old.

They are also two-and-a-half times more likely to have an addiction problem or display suicidal behaviour.

Academic problems found among the children included low IQ scores and low grades.

According to the study's lead author, Dr Brian D'Onofrio, of Indiana University in the US, the researchers were ‘shocked' by these findings.

"The specific associations with paternal age were much, much larger than in previous studies. In fact, we found that advancing paternal age was associated with greater risk for several problems, such as ADHD, suicide attempts and substance use problems, whereas traditional research designs suggested advancing paternal age may have diminished the rate at which these problems occur," he noted.

Dr D'Onofrio insisted that these findings ‘are more informative' than others for a number of reasons, including the sheer number of people studied.

The theory that the researchers worked under was that unlike women, who are born with all their eggs, men produce new sperm continually throughout their lives. Every time sperm replicate, there is the potential for a mutation in the DNA to occur. As men get older, they are exposed to a range of environmental toxins, which have previously been shown to cause mutations in sperm DNA.

Furthermore, studies have found that the sperm of older men tend to have more genetic mutations.

"While the findings do not indicate that every child born to an older father will have these problems, they add to a growing body of research indicating that advancing paternal age is associated with increased risk for serious problems. As such, the entire body of research can help to inform individuals in their personal and medical decision making," Dr D'Onofrio added.

Details of these findings are published in the journal, JAMA Psychiatry.