Children with low IQs could have a higher risk of developing mental disorders such as schizophrenia in adulthood, according to US research.
Studies have linked IQ and mental health, but little is known about how childhood IQ affects the long-term development of mental illness.
This latest study examined 1,037 children born in New Zealand between 1972 and 1973.
IQs were tested once they reached the age of three, and measured again at the ages of seven, nine and 11.
Interviews and tests on overall health and behaviour were carried out every two years between the ages of five and 15 and then again at the ages of 18, 21, 26 and 32.
The researchers then looked for signs of psychiatric disorders in adulthood, between the ages of 18 to 32.
Schizophrenia prevalence was 8.5 per cent among people with a childhood IQ below 85, compared with 2.8 per cent in those with an IQ higher than 115.
No link was found between low childhood IQ and substance-dependence disorders or obsessive-compulsive disorder.
Lead researcher Dr Karestan Koenen, from the Harvard School of Public Medicine in Boston, said: 'Individuals with a lower childhood IQ also had more persistent depression and anxiety and were more likely to be diagnosed with two or more disorders in adulthood.
'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,' she said.
The researchers said low childhood IQ may reveal a difference in the healthy functioning of the brain that makes an individual more vulnerable to certain mental disorders.
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