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IQ and risk for schizophrenia: a population-based cohort study
A S David1, A Malmberg, L Brandt
1Department of Psychological Medicine, King's College School of Medicine and Dentistry, London.
Psychological Medicine
|December 24, 1997
Summary
Low intellectual ability (IQ) is a significant risk factor for developing schizophrenia and other psychoses. This association appears causal, not due to early symptoms or other factors.
Area of Science:
- Psychiatry
- Cognitive Neuroscience
- Epidemiology
Background:
- Investigating the link between cognitive function and psychosis risk.
- Examining low IQ as a potential predictor of schizophrenia and other psychotic disorders.
Purpose of the Study:
- To quantify the association between low IQ and the subsequent development of psychosis.
- To explore the relationship in a large population-based cohort.
Main Methods:
- A cohort of 50,000 Swedish male conscripts (1969-1970) was followed until 1983.
- Cognitive abilities (verbal, visuospatial, general knowledge) and psychosocial factors were assessed at conscription.
- Psychiatric diagnoses were obtained from the Swedish National Register of Psychiatric Care.
Main Results:
- A downward shift in IQ scores was observed in individuals later diagnosed with schizophrenia.
- A linear relationship was found between low IQ and increased schizophrenia risk, even after adjusting for confounders.
- Lower IQ also increased the risk for non-schizophrenic psychoses, though less markedly.
Conclusions:
- Confirms low intellectual ability as a significant risk factor for schizophrenia and other psychoses.
- The association is unlikely to be explained by prodromal decline or known confounders.
- Suggests a potential direct causal link where cognitive impairment influences psychosis, or an indirect link via shared underlying factors like abnormal brain development.