IQ, the Urban Environment, and Their Impact on Future Schizophrenia Risk in Men.
Exposure to an urban environment during early life and low IQ are 2 well-established risk factors for schizophrenia. It is not known, however, how these factors might relate to one another. Data were pooled from the North Jutland regional draft board IQ assessments and the Danish Conscription Registry for men born between 1955 and 1993. Excluding those who were followed up for less than 1 year after the assessment yielded a final cohort of 153170 men of whom 578 later developed a schizophrenia spectrum disorder. We found significant effects of having an urban birth, and also experiencing an increase in urbanicity before the age of 10 years, on adult schizophrenia risk. The effect of urban birth was independent of IQ. However, there was a significant interaction between childhood changes in urbanization in the first 10 years and IQ level on the future adult schizophrenia risk. In short, those subjects who moved to more or less urban areas before their 10th birthday lost the protective effect of IQ. When thinking about adult schizophrenia risk, the critical time window of childhood sensitivity to changes in urbanization seems to be linked to IQ. Given the prediction that by 2050, over 80% of the developed world's population will live in an urban environment, this represents a major future public health issue.
Department of Psychology, Bilkent University, Ankara, Turkey.|Department of Basic and Clinical Neuroscience, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK.|Department of Psychology, The University of Hong Kong, Hong Kong SAR, China.|The State Key Laboratory of Brain and Cognitive Sciences, The University of Hong Kong, Hong Kong SAR, China.
Timothea
T
Toulopoulou
Department of Forensic and Neurodevelopmental Science, Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, UK.
Marco
M
Picchioni
National Centre for Register-based Research, Aarhus University, Aarhus V, Denmark.
Preben Bo
PB
Mortensen
National Centre for Register-based Research, Aarhus University, Aarhus V, Denmark.
Liselotte
L
Petersen
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003718:Denmark / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007360:Intelligence / Q000502:physiology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011157:Population Dynamics / Q000706:statistics & numerical data*; D012042:Registries / Q000706:statistics & numerical data*; D012306:Risk; D012559:Schizophrenia / Q000453:epidemiology* / Q000209:etiology*; D014505:Urban Population / Q000706:statistics & numerical data*; D055815:Young Adult
IQ; future schizophrenia risk; population study; urban birth; urbanicity changes in childhood