Children who experience the death of a family member may have an increased risk of developing psychosis later in life, a new study indicates.

Psychosis refers to a mental state in which a person is detached from reality and experiences a number of abnormal symptoms such as hallucinations, delusions and incoherent thoughts. The most well known psychotic condition is probably schizophrenia.

European and US researchers set out to investigate the potential link between severe stress, as a result of the loss of a loved one in childhood, and psychosis later in life.

Data on children born in Sweden between 1973 and 1985 was analysed - this amounted to almost 950,000 children. Among these, one in three experienced the death of a family member before they had reached the age of 13. While most of these deaths were from natural causes, a small number was due to suicide and accidents.

The researchers also looked at exposure to this type of stress when the children were still in the womb.

The study found no increased risk of psychosis if the child was exposed to this kind of stress prenatally, i.e. while still in the womb. However it did find a small but significant increased risk if the child experienced the death of someone in their immediate family, i.e. a parent or sibling, up to the age of 13.

Furthermore, the younger they were at the time of the death, the higher the risk of subsequent psychosis. The biggest risk was found in children aged three or under.

The risk of developing psychosis later on was greatest if the family member had died by suicide. This was followed by accidents and then natural causes.

"Our research shows childhood exposure to death of a parent or sibling is associated with excess risk of developing a psychotic illness later in life. This is particularly associated with early childhood exposure. Further investigation is now required," commented Prof Kathryn Abel of the University of Manchester in the UK.

Details of these findings are published in the British Medical Journal.