Children born to an older father run a greater risk of developing a bipolar disorder than other kids, a Swedish study showed on Tuesday.
"Children whose father was 55 years old or more (at the time of conception) run about a 37-percent greater risk of suffering from (bipolar disorder) than children whose fathers were in their 20s," Emma Frans, a researcher at Karolinska Institute in Stockholm, told AFP.
Bipolar disorder, also known as manic depression, is a severe mood disorder involving alternating episodes of mania and depression.
The study surveyed more than 13,000 patients in Sweden diagnosed with bipolar disorder, and found that the older their fathers were the more likely they were to have the condition.
Frans said the explanation was genetic.
"Unlike women, men's reproductive cells continue to divide throughout their lifetime, which increases the risk of DNA copy errors over the years," she said.
The offspring of older mothers also had an increased risk, but it was less pronounced that the paternal effect, the study said.
Older fathers have previously been identified as one of the factors behind other disorders such as schizophrenia and autism.
About one percent of the Swedish population suffers from bipolar disorder, the study said.