When talking about a biological clock, we are usually referring to women. However, a study published in April 2014 by the medical journal JAMA Psychiatry, shows that men have a sort of biological clock as well that can affect psychiatric health of offsprings.

Conducted in Sweden the large study set out to examine the association between advancing paternal age and an offspring’s psychiatric well-being. Researchers collected and analyzed data from 2.6 million children born between 1973 and 2001, making it one of the largest and most comprehensive studies of the effects of paternal age.

Compared to younger fathers, older fathers’ children were found to be significantly more at risk for a host of psychiatric disorders. For example, the children of fathers ages 45 and over were three times more likely to have an autism spectrum disorder, 13 times more likely to have ADHD, and 25 times more likely to have bipolar disorder than the children of fathers aged 20 to 24.

Why does this occur?

The study’s author and associate professor in the Department of Psychological and Brain Sciences at Indiana University, Brian D’Onofrio, explains that as men get older and male sperm continues to replicate throughout a lifetime, there are more chances of having mutations in the base pairs of the DNA. Those genetic mutations are associated with psychiatric problems, such as autism, attention-deficit/hyperactivity disorder, and biopolar disorder.

A similar study conducted in Iceland in 2012, indicated that as many as 20% to 30% of cases of autism and schizophrenia may be linked to fathers’ advanced age. This study also concluded that, unlike conditions such as Down Syndrome, the mother’s age made no difference.

Comparing Apples to Apples

Most previous studies on the subject simply compare children born to young fathers with those of older fathers. D’Onofrio wanted to minimize the many factors in comparing younger men to older men that could compromise the results. He saw the earlier methods as “comparing apples and oranges.” Instead, D’Onofrio and his colleagues compared siblings to consider the outcomes when the same man has child in his younger years and then again later in life.