Having very young or very old parents makes you more likely to have bipolar disorder, research suggests.
An international team of researchers looked at data for almost 14million people from existing studies, comparing rates of the condition to parent age.
They found a U-shaped curve, where the youngest and oldest ages were associated with the highest risk.
Fathers over the age of 45 were almost 30 cent more likely to have a child that became bipolar later in life, compared to fathers aged 25 to 29.
Women over 35 were also 20 per cent more likely to have a child with bipolar disorder.
In younger parents below the age of 20, there was a 23 per cent (for mothers) and 29 per cent (for fathers) increased risk.
Study leader Dr Giovanna Fico, a psychiatrist at the University of Barcelona, said: ‘What we have found is slightly unusual because both younger and older parents carry an increased risk of having a child with bipolar disorder.
‘The increased risk is moderate, but real.’
Having a father who was over the age of 45 and a mother who was over 35 when you were born significantly increases your chance of having of bipolar disorder. Children of very young parents are also more at risk
WHAT IS BIPOLAR?
Bipolar disorder is a brain disorder which causes unusual and often sudden changes in mood and energy levels.
WHAT ARE THE SYMPTOMS?
Moods of those with bipolar disorder range from periods of extreme elation and energy (known as a manic episode) to periods of extreme somberness and lack of energy (known as a depressive episode).
HOW IS IT DIAGNOSED?
According to the International Bipolar Foundation, sufferers are diagnosed with rapid cycling if they have four or more manic, hypomanic, or depressive episodes in any 12-month period.
This severe form of the condition occurs in around 10 to 20 percent of all people with bipolar disorder.
WHAT CAUSES IT?
Currently it is unknown what is the cause of bipolar disorder, which affects around 5.7 million US adults aged 18 or older.
Scientists say genetics could play a role or that those with a a family history of bipolar disorder are more likely to have it.
Dr Fico said researchers ‘don’t really know’ why young and old parents carry the risk.
She said that for younger parents, it could be due to environmental factors like socio-economic problems, a lack of support, as well as stress.
In older parents, it may be down to genetic factors.
Bipolar disorder is one of the most common serious mental illnesses, where people suffer huge mood swings from elation to extreme depression.
It carries a high-risk of suicide and premature death, and is known to have a strong genetic link.
If either parent has bipolar disorder, there is a 15 to 30 per cent chance this will be passed down to their children.
The researchers, from Spain, Italy, Australia and the Netherlands, reviewed studies from around the world which looked at bipolar disorder and age.
The studies included a total of 13,424,760 participants — with 217,089 who had the disorder.
Professor Maj Vinberg, professor of psychiatry at the University of Copenhagen, who was not involved in the research, said the link between age and bipolar risk could be because younger people with the disorder are more likely to have unprotected sex during their manic phases, and therefore pass it on.
He said: ‘The study raises several exciting research questions, including the possibility of early prevention and intervention.
‘For example, in the daily clinical settings, it is crucial to be aware that young individuals with bipolar disorder in their manic phases have more risky sexual behavior, which can associate with an increased pregnancy risk.’
Dr Fico added: ‘We must stress that this risk is moderate, and it must be kept in perspective.
‘However, for those already at risk, age is another factor that should be taken into consideration, and so it may be that doctors need to counsel both younger and older couples if they have a risk of bipolar disorder.’
Very young or very old parents also have a higher risk of an autistic child, Dr Fico said.
The findings were published in the journal European Neuropsychopharmacology.
Bipolar disorder affects around 5.7million US adults, and 3million people in the UK.