IQ and mental disorder in young men.
BACKGROUND
Most research investigating the relationship between IQ and risk of mental disorder has focused on schizophrenia.


OBJECTIVE
To illuminate the relationship between IQ test scores in early adulthood and various mental disorders.


METHODS
For 3289 men from the Copenhagen Perinatal Cohort, military IQ test scores and information on psychiatric hospitalisation were available. We identified 350 men in the Danish Psychiatric Central Register, and compared the mean IQ test scores of nine diagnostic categories with the mean scores of 2939 unregistered cohort controls.


RESULTS
Schizophrenia and related disorders, other psychotic disorders, adjustment, personality, alcohol and substance-use-related disorders were significantly associated with low IQ scores, but this association remained significant for the four non-psychotic disorders only when adjusting for comorbid diagnoses. For most diagnostic categories, test scores were positively associated with the length of the interval between testing and first admission. ICD mood disorders as well as neuroses and related disorders were not significantly associated with low IQ scores.


CONCLUSIONS
Low IQ may be a consequence of mental disease or a causal factor in psychotic and non-psychotic disorders.
Mortensen
Erik Lykke
EL
Department of Health Psychology, Institute of Public Health, University of Copenhagen, Øster Farimagsgade 5A, PO Box 2099, 1014 Copenhagen K, Denmark. e.l.mortensen@pubhealth.ku.dk
Sørensen
Holger Jelling
HJ
Jensen
Hans Henrik
HH
Reinisch
June Machover
JM
Mednick
Sarnoff A
SA
D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D015897:Comorbidity; D003718:Denmark / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007360:Intelligence; D007361:Intelligence Tests; D008297:Male; D001523:Mental Disorders / Q000453:epidemiology / Q000523:psychology*; D011446:Prospective Studies; D012565:Schizophrenic Psychology; D012923:Social Class; D019966:Substance-Related Disorders / Q000523:psychology