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Cognitive function and other risk factors for mild traumatic brain injury in young men: nationwide cohort study

BMJ 2013; 346 doi: (Published 13 March 2013) Cite this as: BMJ 2013;346:f723
  1. Anna Nordström, associate professor1,
  2. Benoni B Edin, professor2,
  3. Sara Lindström, research scientist3,
  4. Peter Nordström, professor4
  1. 1Department of Community Medicine and Rehabilitation, Rehabilitation Medicine, Umeå University, SE-901 87 Umeå, Sweden
  2. 2Department of Integrative Medical Biology, Physiology Section, Umeå University
  3. 3Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA
  4. 4Department of Community Medicine and Rehabilitation, Geriatric Medicine, Umeå University
  1. Correspondence to: A Nordström anna.nordstrom{at}
  • Accepted 18 January 2013


Objective To investigate cognitive function and other risk factors for mild traumatic brain injury in young men.

Design Nationwide prospective cohort study.

Setting Sweden.

Participants 305 885 men conscripted for military service from 1989 to 1994.

Main outcome measure mild traumatic brain injuries in relation to cognitive function and other potential risk factors assessed at conscription and follow-up.

Results Men with one mild traumatic brain injury within two years before (n=1988) or after cognitive testing (n=2214) had about 5.5% lower overall cognitive function scores than did men with no mild traumatic brain injury during follow up (P<0.001 for both). Moreover, men with at least two mild traumatic brain injuries after cognitive testing (n=795) had 15% lower overall cognitive function scores compared with those with no such injury (P<0.001). Independent strong risk factors (P<1×10−10) for at least one mild traumatic brain injury after cognitive testing (n=12 494 events) included low overall cognitive function, a previous mild traumatic brain injury, hospital admission for intoxications, and low education and socioeconomic status. In a sub-cohort of twin pairs in which one twin had a mild traumatic brain injury before cognitive testing (n=63), both twins had lower logical performance and technical performance compared with men in the total cohort with no mild traumatic brain injury (P<0.05 for all).

Conclusion Low cognitive function, intoxications, and factors related to low socioeconomic status were strong independent risk factors for mild traumatic brain injuries in men. The low cognitive function in twin pairs discordant for mild traumatic brain injury suggests a genetic component to the low cognitive function associated with such injuries. The study included only men, so inferences to women should be made with caution.


  • Contributors: PN and AN developed the idea for the study. PN compiled and analysed the study estimates with help and input from AN, SL, and BBE. AN made initial drafts of tables and figures with input from PN, SL, and BBE. AN led the writing of the paper, with contributions from all other authors. PN is the guarantor.

  • Funding: The study was funded by the Swedish Research Council. The researchers conducted this study totally independently of the funding body.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: support from the Swedish Research Council for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: This study was approved by the regional ethics board in Umeå and by the National Board of Health and Welfare in Sweden.

  • Data sharing: No additional data available.

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