High intelligence linked to reduced risk of schizophrenia

People with high intelligence may be less likely to develop schizophrenia, particularly those who have a genetic susceptibility to the condition. This is according to a new study published in The American Journal of Psychiatry.

The researchers, including first author Dr. Kenneth S. Kendler of the Virginia Commonwealth University, say their findings challenge past studies indicating that people who are intelligent are more likely to be mentally ill.

“If you’re really smart, your genes for schizophrenia don’t have much of a chance of acting,” says Dr. Kendler.

Schizophrenia is a disabling brain disorder that affects around 2.4 million adults in the US. Onset of the condition usually occurs in early adolescence, and it is characterized by hallucinations, delusions, abnormal thoughts and agitated body movements.

The exact causes of schizophrenia are unclear, but scientists have established that the disorder is familial; around 1% of the general population have schizophrenia, but it occurs in around 10% of people who have have a first-degree relative – such as a parent, brother or sister – with the condition.

In this study, Dr. Kendler and colleagues set out to assess the association between IQ and subsequent schizophrenia risk among the general population and those have a genetic predisposition for the disorder.

Not achieving predicted IQ ‘most strongly predisposes for schizophrenia’

The team assessed the IQ at ages 18-20 years of 1,204,983 Swedish males who were born between 1951 and 1975.

The researchers used Cox proportional hazard models to calculate how IQ influences schizophrenia risk among the general population and among cousin, half-sibling and full-sibling pairs, some of which had a relative with the condition.

Up until 2010, the team monitored any schizophrenia-related hospital admissions among the participants.

The results of the analysis revealed that individuals with a low IQ were more likely to develop schizophrenia than those with a high IQ. This relationship was strongest among participants with a family history of the disorder; among cousin, half-sibling and full-sibling pairs, the individual with the lowest IQ was at highest risk for schizophrenia.