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IQ and mental disorder in young men
Erik Lykke Mortensen1, Holger Jelling Sørensen, Hans Henrik Jensen
1Department of Health Psychology, Institute of Public Health, University of Copenhagen, Øster Farimagsgade 5A, PO Box 2099, 1014 Copenhagen K, Denmark. e.l.mortensen@pubhealth.ku.dk
The British Journal of Psychiatry : the Journal of Mental Science
|November 2, 2005
Summary
Low IQ scores are linked to several mental health conditions, including psychotic and non-psychotic disorders. This association suggests IQ may be a risk factor or consequence of mental illness.
Area of Science:
- Psychiatry
- Psychology
- Epidemiology
Background:
- Previous research on IQ and mental disorder risk primarily focused on schizophrenia.
- The relationship between general intelligence and a broader spectrum of mental disorders requires further investigation.
Purpose of the Study:
- To examine the association between early adulthood IQ test scores and the risk of various mental disorders.
- To determine if lower IQ is a predictor for developing specific psychiatric conditions.
Main Methods:
- Utilized data from 3289 men in the Copenhagen Perinatal Cohort, including military IQ test scores.
- Compared mean IQ scores of 350 individuals with psychiatric hospitalizations across nine diagnostic categories against 2939 controls.
- Information on psychiatric hospitalizations was sourced from the Danish Psychiatric Central Register.
Main Results:
- Significant associations were found between low IQ scores and schizophrenia, other psychotic disorders, adjustment disorders, personality disorders, and alcohol/substance-use disorders.
- The association for four non-psychotic disorders remained significant after adjusting for comorbid diagnoses.
- A positive correlation was observed between IQ scores and the time interval between testing and first psychiatric admission for most diagnostic categories.
- No significant association was found between low IQ scores and ICD mood disorders or neuroses.
Conclusions:
- Low IQ may serve as a causal factor contributing to the development of both psychotic and non-psychotic mental disorders.
- Alternatively, low IQ could be a consequence of developing mental illness.
- The findings highlight the complex interplay between cognitive function and mental health across a range of conditions.