Having a high IQ might reduce your risk of developing schizophrenia

US and Swedish scientists have determined that having high intelligence could actually protect a person with a genetic predisposition for schizophrenia from developing the condition, which goes against the conventional wisdom that brilliance and schizophrenia share a link.

Schizophrenia is a disabling brain disorder that affects language, perception and the sense of self. Onset of the condition begins in late adolescence and is marked by hallucinations, delusions and problems with feelings, behaviour and motivation.

According to the World Health Organisation (WHO), over 21 million people suffer from the condition and at least half of them are not receiving treatment and care for their condition.

Researchers from Virginia Commonwealth University in the US and Lund University in Sweden conducted the world's largest study of IQ and schizophrenia to date, studying over 1.2 million Swedish males born between 1951 and 1975.

Largest study into IQ and schizophrenia

The results of their research, entitled "IQ and Schizophrenia in a Swedish National Sample: Their Causal Relationship and the Interaction of IQ with Genetic Risk", has been published in the American Journal of Psychiatry.

The IQ of the participants was studied at ages 18 to 20, and any hospitalisation relating to schizophrenia was tracked for 24 years until 2010.

The researchers found that the men who had a lower IQ than their siblings had the highest risk for developing schizophrenia.

"If you're really smart, your genes for schizophrenia don't have much of a chance of acting," said Kenneth S. Kendler, MD, professor of psychiatry and human and molecular genetics at Virginia Commonwealth University who led the study.

Lower IQ can mean a higher risk

"What really predicted risk for schizophrenia is how much you deviate from the predicted IQ that we get from your relatives.

"If you're quite a bit lower, that carries a high risk for schizophrenia. Not achieving the IQ that you should have based on your genetic constitution and family background seems to most strongly predispose for schizophrenia."

Environmental factors that could diminish a person's IQ include early drug use, body size at birth and childhood trauma.

Of course, this does not mean that someone with a high IQ will never develop schizophrenia, but the commonly-held belief that brilliance and schizophrenia share a link is not true.

"The question is, might we see some upward bump at that high level of intelligence where really brilliant people have increased risk for the disease and we show no such trend," said Kendler.