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Children who experience severe trauma are three times more likely to suffer from schizophrenia when they grow up, a new study found.

For many years research in mental health has focused on the biological factors behind conditions such as schizophrenia, bipolar disorder and psychotic depression. But the results of the research add to a growing body of evidence that childhood maltreatment or abuse can raise the risk of developing mental illnesses in adulthood.

Lead researcher Richard Bentall from the University of Liverpool's Institute of Psychology, Health and Society, said, "The causes of psychotic disorders, particularly schizophrenia, are a source of controversy amongst psychiatrists, psychologists and doctors. There is also disagreement about how the disorders are defined. It's not unusual, for example, for a patient to be diagnosed with schizophrenia by one psychiatrist, but as bipolar by another."

"Our findings suggest that studies on the neurological and genetic factors associated with these conditions, which are not yet fully understood, are more like to advance our knowledge if we take into account a patient's life experiences. We need to know, for example, how childhood trauma affects the developing brain, as well as whether there are genetic factors that increase vulnerability or resilience to traumatic events."

The research brought together and analysed the findings from more than 30 years of studies looking at the association between childhood trauma and the development of psychosis. The team looked at more than 27,000 research papers to extract data from three types of studies; those addressing the progress of children known to have experienced adversity; studies of randomly selected members of the population; and research on psychotic patients who were asked about their early childhood.

Across all three types of studies the results led to similar conclusions. Children who had experienced any type of trauma before the age of 16 were approximately three times more likely to become psychotic in adulthood compared to those selected randomly from the population. Th authors found a relationship between the level of trauma and the likelihood of developing illness in later life. Those that were severely traumatized as children were at a greater risk, in some cases up to 50 times increased risk, than those who experienced trauma to a lesser extent.

The team also conducted a new study which looked at the relationship between specific psychotic symptoms and the type of trauma experienced in childhood. They found that different traumas led to different symptoms. Childhood sexual abuse, for example, was associated with hallucinations, while being brought up in a children's home was associated with paranoia. The research further suggests a strong relationship between environment and the development of psychosis, and provides clues about the mechanisms leading to severe mental illness.

"Now that we know environment is a major factor in psychosis and that there are direct links between specific experiences and symptoms of the condition, it is even more vital that psychiatric services routinely question patients about their life experience. Surprisingly, some psychiatric teams do not address these issues and only focus on treating a patient with medication," said Bentall.

The researchers will now look the psychological and brain processes involved in the links between different types of trauma and particular psychotic symptoms. Future research will also aim to discover why symptoms of psychosis may only be expressed in later life, when the initial trigger many have been many years before in childhood.

The research is published in Schizophrenia Bulletin.