Having a lower IQ increases the risk of developing schizophrenia, according to a recent study.
Based on an examination of more than 1.2 million Swedish men, Kenneth Kendler, MD, of Virginia Commonwealth University in Richmond, and colleagues found that each 1-point decrease in an individual’s IQ score is associated with a 3.7% increased risk of developing schizophrenia.
The men, who were born between 1951 and 1975, had their IQ tested when they were between the ages of 18 and 20. Potential schizophrenia diagnosis was assessed until 2010.
A negative monotonic relationship between IQ and schizophrenia was observed, starting with a relatively steep slope in those in the low IQ range, and then a decline in slope as IQ scores increased, the team reported in The American Journal of Psychiatry.
The study undermines an argument that there is a fine line between genius and schizophrenia. “Risk for schizophrenia in our highest IQ category was lower than that in the next highest group,” the researchers wrote.
They also found that a theory that the relationship between IQ and schizophrenia can be affected by genetic or environmental factors is unfounded. “Within pairs of relatives with differing IQs, the association between intelligence and schizophrenia was as strong as in the general population,” the researchers say.
The risk for developing schizophrenia is significantly affected by an individual’s IQ, show results of a study of over 1 million Swedish men.
Researchers found that each 1-point decrease in IQ score was associated with a 3.8% increase in the risk of developing schizophrenia.
“The observed IQ-schizophrenia association does not, to any appreciable degree, appear to result from declines in intelligence in individuals undergoing an insidious onset of schizophrenia at the time of testing”, note Kenneth Kendler (Virginia Commonwealth University, Richmond, Virginia) and co-authors in The American Journal of Psychiatry.