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Intelligence in early adulthood and subsequent hospitalization for mental disorders
Catharine R Gale1, G David Batty, Per Tynelius
1MRC Epidemiology Resource Centre, University of Southampton, Southampton, United Kingdom.
Epidemiology (Cambridge, Mass.)
|November 13, 2009
Summary
Lower intelligence is a significant risk factor for all mental disorders, increasing hospital admission rates. This association with lower IQ scores also correlates with greater illness severity and comorbidity across various psychiatric conditions.
Area of Science:
- Psychiatry and Psychology
- Epidemiology
- Cognitive Science
Background:
- Lower intelligence is a known risk factor for specific mental disorders.
- The relationship between premorbid intelligence and the risk for all mental disorders, as well as illness severity, remains unclear.
- This study investigates the association between premorbid intelligence and hospital admission rates for the full spectrum of mental disorders.
Purpose of the Study:
- To examine the association between premorbid intelligence and the risk of hospital admission for all mental disorders.
- To investigate the link between premorbid intelligence and the total admission rates for mental disorders, as a potential indicator of clinical severity.
- To determine if lower intelligence is a risk factor across the entire range of mental disorders and for illness severity.
Main Methods:
- A cohort of 1,049,663 Swedish men was studied.
- Participants underwent intelligence testing during military conscription.
- Follow-up data on hospital admissions for mental disorders, with diagnoses from the International Classification of Diseases, were collected over a mean of 22.6 years.
Main Results:
- Risk of hospital admission increased with each point decrease in IQ score for all mental disorder categories.
- A one standard deviation decrease in IQ was associated with significantly elevated hazard ratios for schizophrenia, nonaffective psychoses, mood disorders, neurotic disorders, adjustment disorders, personality disorders, and alcohol- and substance-use disorders.
- Lower intelligence was also linked to increased comorbidity and higher total admission rates, suggesting greater clinical severity.
Conclusions:
- Lower premorbid intelligence is a robust risk factor for the entire spectrum of mental disorders.
- The findings indicate a significant association between lower intelligence and increased mental disorder risk and clinical severity.
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