title: Schizophrenia and the city: A review of literature and prospective study of psychosis and urbanicity in Ireland.
abstract: Urbanicity has been repeatedly associated with increased incidence of schizophrenia. This article (a) presents results of a prospective study of urbanicity and schizophrenia in Ireland and (b) reviews the literature relating to urbanicity and schizophrenia. We prospectively compared incidence of schizophrenia and other psychoses in urban and rural catchment areas (over 4years and 7years, respectively) using face-to-face, DSM-III-R diagnostic interviews. Incidence of schizophrenia in males was higher in urban compared to rural areas, with an age-adjusted incidence rate ratio (IRR) of 1.92 (1.52-2.44) for males and 1.34 (1.00-1.80) for females. Incidence of affective psychosis was lower in urban compared to rural areas for males (IRR 0.48; 0.34-0.67) and females (IRR 0.60; 0.43-0.83). These findings are consistent with the literature, which provides persuasive evidence that risk for schizophrenia increases with urban birth and/or upbringing, especially among males. Register-based studies support this conclusion more consistently than studies using face-to-face diagnostic interviews, the difference being related to power. The mechanism of association is unclear but may relate to biological or social/environmental factors or both, acting considerably before psychotic symptoms manifest. There is a diversity of potential candidates, including air pollution, cannabis and social exclusion. Urbanicity may have a synergistic effect with genetic vulnerability. Future research is likely to focus on the relationship between urbanicity and neural maldevelopment, the possibility of rural protective factors (e.g. social capital, low social fragmentation), urbanicity in developing countries, cultural variables and geographical location, and associations between urbanicity and other disorders (e.g. affective psychosis).
authors.affiliation: Department of Psychiatry, University College Dublin, Dublin 7, Ireland. brendankelly35@gmail.com
authors.forename: Brendan D
authors.initials: BD
authors.lastname: Kelly
authors.forename: Eadbhard
authors.initials: E
authors.lastname: O'Callaghan
authors.forename: John L
authors.initials: JL
authors.lastname: Waddington
authors.forename: Larkin
authors.initials: L
authors.lastname: Feeney
authors.forename: Stephen
authors.initials: S
authors.lastname: Browne
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Scully
authors.forename: Mary
authors.initials: M
authors.lastname: Clarke
authors.forename: John F
authors.initials: JF
authors.lastname: Quinn
authors.forename: Orflaith
authors.initials: O
authors.lastname: McTigue
authors.forename: Maria G
authors.initials: MG
authors.lastname: Morgan
authors.forename: Anthony
authors.initials: A
authors.lastname: Kinsella
authors.forename: Conall
authors.initials: C
authors.lastname: Larkin
mesh_terms: D017677:Age Distribution; D002947:Cities / Q000453:epidemiology*; D016001:Confidence Intervals; D016208:Databases, Factual / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D007494:Ireland / Q000453:epidemiology; D008297:Male; D011446:Prospective Studies; D011569:Psychiatric Status Rating Scales; D012189:Retrospective Studies; D012424:Rural Population; D012559:Schizophrenia / Q000453:epidemiology*; D012737:Sex Factors; D012931:Social Environment; D014505:Urban Population / Q000706:statistics & numerical data*