MedWire News: Having an older father increases the risk of developing bipolar disorder, indicate the results of a Swedish study published in the journal Archives of General Psychiatry.

Bipolar disorder is associated with few risk factors other than a family history of mental illness. Still, many bipolar patients do not have family members with the disease, suggesting there are other contributing factors.

Lead investigator Dr Emma Frans, from the Karolinska Institute in Stockholm, and team explored the potential association between father's age and the risk of bipolar disorder in 13,428 patients. All participants had been hospitalised on at least two separate occasions.

After adjusting for factors such as mother's age, economic and social status, and family history of psychotic disorder, the team found that children of men aged 55 years and older were 1.5 times more likely to develop bipolar disorder than children of men aged 20-24 years.

The effects of the father's age were even stronger in patients who developed bipolar disorder at a young (less than 20 years) age. In this group, study findings showed that advancing parental age was associated with more than a 2.5 times greater odds of developing bipolar disorder.

The research team concludes that, similar to other severe mental illness such as schizophrenia and autism, advanced age in the father increases the risk that children will develop bipolar disorder. This increased risk is believed to be driven mainly by genetic factors.