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Low intelligence test scores in 18 year old men and risk of suicide: cohort study

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.38310.473565.8F (Published 20 January 2005) Cite this as: BMJ 2005;330:167
  1. D Gunnell, professor of epidemiology1,
  2. P K E Magnusson, researcher2,
  3. F Rasmussen, senior clinical lecturer and associate professor of epidemiology (finn.rasmussen{at}phs.ki.se)3
  1. 1 Department of Social Medicine, University of Bristol, Bristol BS8 2PR,
  2. 2 Department of Genetics and Pathology, Rudbeck Laboratory, Uppsala University, Sweden,
  3. 3 Child and Adolescent Public Health Epidemiology Group, Department of Public Health Sciences, Karolinska Institutet, SE-17176 Stockholm, Sweden
  1. Correspondence to: F Rasmussen
  • Accepted 9 November 2004

Abstract

Objective To examine the association between intelligence test scores in men, measured at age 18, and subsequent suicide.

Design Record linkage study of the Swedish military service conscription register (1968-94) with the multi-generation register, cause of death register and census data. Four tests were performed at conscription covering logic, language, spatial, and technical skills.

Setting Sweden.

Participants 987 308 Swedish men followed up for 5-26 years.

Main outcome measure Suicide.

Results 2811 suicides occurred during follow up. The risk of suicide was two to three times higher in those with lowest compared with the highest test scores. The strongest associations were seen with the logic test: for each unit increase in test score the risk of suicide decreased by 12% (95% confidence interval 10% to 14%). Associations were only slightly attenuated when we controlled for parents' socioeconomic position. Greatest risks were seen among poorly performing offspring of well educated parents.

Conclusions Performance in intelligence tests is strongly related to subsequent risk of suicide in men. This may be due to the importance of cognitive ability in either the aetiology of serious mental disorder or an individual's capacity to solve problems while going through an acute life crisis or suffering from mental illness.

Footnotes

  • Contributors DG, PKEM, and FR developed the core idea. FR and PKEM designed the study. FR prepared the cohort data and did the database linkages. PKEM conducted all statistical analysis. DG conducted the literature search and wrote the first draft of the paper. All authors critically reviewed and contributed to the final draft of the paper and all are guarantors.

  • Funding PKEM is funded by The Beijer Foundation.

  • Competing interests None declared.

  • Ethical approval The ethics committee at the Karolinska Institute, Stockholm, Sweden, approved the study.

  • Accepted 9 November 2004
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