Psychosis alters association between IQ and future risk of attempted suicide: cohort study of 1 109 475 Swedish menBMJ 2010; 340 doi: https://doi.org/10.1136/bmj.c2506 (Published 03 June 2010) Cite this as: BMJ 2010;340:c2506
- G David Batty, Wellcome Trust fellow123,
- Elise Whitley, medical statistician1,
- Ian J Deary, professor of differential psychology2,
- Catharine R Gale, reader in epidemiology4,
- Per Tynelius, statistician5,
- Finn Rasmussen, professor5
- 1Medical Research Council Social and Public Health Sciences Unit, University of Glasgow, Glasgow
- 2Centre for Cognitive Ageing and Cognitive Epidemiology, Department of Psychology, University of Edinburgh, Edinburgh
- 3The George Institute for International Health, University of Sydney, Sydney, Australia
- 4Medical Research Council Epidemiology Resource Centre, University of Southampton, Southampton
- 5Child and Adolescent Public Health Epidemiology Group, Department of Public Health Sciences, Karolinska Institute, SE-17176 Stockholm, Sweden
- Correspondence to: F Rasmussen
- Accepted 9 March 2010
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.
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.
Contributors: All authors contributed to the design and interpretation of the study, critically revised the manuscript, and approved the final version. EW did the statistical analyses, and GDB and EW wrote the first draft. EW, PT, and FR are the guarantors.
Funding: GDB is a Wellcome Trust fellow (WBS U.1300.00.006.00012.01), funding from which also supports EW. The Medical Research Council (MRC) Social and Public Health Sciences Unit receives funding from the UK MRC and the Chief Scientist Office at the Scottish Government Health Directorates. The Centre for Cognitive Ageing and Cognitive Epidemiology is supported by the Biotechnology and Biological Sciences Research Council, the Engineering and Physical Sciences Research Council, the Economic and Social Research Council, the MRC, and the University of Edinburgh as part of the cross council lifelong health and wellbeing initiative. FR is supported by the Swedish Research Council, the Labour Market Insurance Ltd (AFA), and the Swedish Council for Working Life and Social Research.
Competing interests: None declared.
Ethical approval: The Regional Ethics Committee, Stockholm, approved the study.
Data sharing: No additional data available.
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.