NZ researchers link low childhood IQ to depression

A new study of has revealed a connection between low childhood IQ and psychiatric disorders later in life in New Zealanders.

Researchers at the Harvard School of Public Health say of 1037 children born in Dunedin in 1972 and 1973 those with lower IQs had an increased risk of developing psychiatric disorders such as schizophrenia, depression and generalised anxiety disorder.

The children were members of the Dunedin Multidisciplinary Health and Development Study, which made its initial assessment of the children at age three, an online preview of new longterm study says.

The results are due to be published in The American Journal of Psychiatry in January.

The participants were also interviewed and tested on their overall health and behaviour at ages five, seven, nine, 11, 13, 15, 18, 21, 26 and at age 32.

"Lower childhood IQ predicted increased risk of schizophrenia, depression and generalised anxiety disorder," study lead author Karestan Koenen, assistant professor of society, human development, and health at Harvard University, said.

"Individuals with lower childhood IQ also had more persistent depression and anxiety and were more likely to be diagnosed with two or more disorders in adulthood."

No association was found between lower childhood IQ and substance dependence disorders, simple phobia, panic disorder or obsessive-compulsive disorder.

The researcher said the mechanism through which lower childhood IQ might lead to increased risk of adult anxiety disorders was not known, but suggested the lower IQ in childhood might reveal a difference in brain health that makes an individual more vulnerable to certain mental disorders.

Another possible mechanism was stress - people with lower childhood IQ were less equipped to deal with complex challenges of modern daily life, which may make them more vulnerable to developing mental disorders.

The findings may be helpful in treating individuals with mental health disorders, according to the researchers.

"Lower childhood IQ was associated with greater severity of mental disorders including persistence over time and having two or more diagnoses at age 32," said Prof Koenen.

"Since individuals with persistent and multiple mental disorders are more likely to seek services, cognitive ability may be an important factor for clinicians to consider in treatment planning.

"Individuals with lower cognitive ability may find it harder to follow instructions and comply with treatment regimens. By taking clients' cognitive ability into account, clinicians may improve treatment outcome."

The results may also be helpful in prevention planning.

"Educators and paediatricians should be aware that children with lower cognitive ability may be at greater risk of developing psychiatric disorders," Prof Koenen said.

"Early detection and intervention aimed at ameliorating mental health problems in these children may prevent these problems from carrying over into adulthood."

- NZPA