Psychological Medicine

Original Articles

The epidemiology of chronic fatigue in the Swedish Twin Registry

a1 Department of Laboratory Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden
a2 Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
a3 Department of Psychology, University of Southern California, CA, USA
a4 Departments of Genetics, Psychiatry & Epidemiology, University of North Carolina at Chapel Hill, NC, USA

Article author query
evengard b   [PubMed][Google Scholar] 
jacks a   [PubMed][Google Scholar] 
pedersen nl   [PubMed][Google Scholar] 
sullivan pf   [PubMed][Google Scholar] 


Background. Chronic fatigue syndrome (CFS) remains an idiopathic and controversial entity.

Method. We screened 31405 individual members of the Swedish Twin Registry (aged 42–64 years) for the symptoms of fatiguing illness via a telephone questionnaire. We refined self-reported symptoms via data from several national registries and from physician review of all available medical records in order to approximate closely the dominant case definition of CFS.

Findings. The 6-month prevalence of CFS-like illness was 2·36% (95% CI 2·19–2·53) and was markedly higher in women than men, odds ratio 3.92 (95% CI 3·24–4·72) with no significant association with age or years of education. There was a highly significant association with occupation that disappeared after accounting for gender.

Interpretation. CFS-like illness may be more common that previously acknowledged. There is a marked increase in risk by gender. Previous reports that CFS is more prevalent in individuals in certain occupational categories were not confirmed and may have been due to confounding by gender.

c1 FRANZCP, Department of Genetics, CB #7264, 4109D Neurosciences Research Building, University of North Carolina, Chapel Hill, NC, 27599-7264, USA. (Email: