Psychosis alters association between IQ and future risk of attempted suicide: cohort study of 1 109 475 Swedish men

Objectives To explore associations between IQ measured in early adulthood and subsequent hospital admissions for attempted suicide and to explore the role of psychosis and examine associations of IQ with specific methods of attempted suicide. Design Cohort study. Setting Sweden. Participants 1 109 475 Swedish men with IQ measured in early adulthood followed up for an average 24 years. Main outcome measures Hospital admission for attempted suicide. Results 17 736 (1.6%) men had at least one hospital admission for attempted suicide by any means during follow-up. After adjustment for age and socioeconomic status, lower IQ scores were associated with an elevated risk of attempted suicide by any means (hazard ratio per standard deviation decrease in IQ=1.57, 95% confidence interval 1.54 to 1.60), with stepwise increases in risk across the full IQ range (P for trend<0.001). Similar associations were observed for all specific methods of attempted suicide. Separate analyses indicated that associations between IQ and attempted suicide were restricted to participants without psychosis and that IQ had no marked impact on risk of attempted suicide in those with psychosis. Conclusions Low IQ scores in early adulthood were associated with a subsequently increased risk of attempted suicide in men free from psychosis. A greater understanding of the mechanisms underlying these associations may provide opportunities and strategies for prevention.