No evidence of time trends in the urban–rural differences in schizophrenia risk among five million people born in Denmark from 1910 to 1986

Abstract

There was no evidence of time trends in the urban-rural differences in the incidence of schizophrenia in Denmark, suggesting that the cause(s) responsible for these differences were not related to exposures that became more prevalent in urban areas over time. This finding is in contrast to findings from Finland and The Netherlands.

Persons with schizophrenia migrate towards urban areas due to the development of their disorder or its prodromata

“…The prospective studies of urban-rural differences in the risk of schizophrenia have typically relied on nationwide population-based registers including the clinical diagnoses registered (e.g. (Eaton et al, 2000;Haukka et al, 2001;Lewis et al, 1992;Marcelis et al, 1998;Marcelis et al, 1999;Mortensen et al, 1999;Pedersen et al, 2004;Pedersen, 2006;Pedersen and Mortensen, 2001a;Pedersen and Mortensen, 2001b;). …”

“…Place of birth and residence in Denmark were classified according to the degree of urbanization (Statistics, 1997) (numbers are persons per square kilometer): capital 5220; capital suburb 845; provincial cities 470; provincial towns 180; rural areas 55, as done previously (Pedersen, 2006). Residential information on municipality from 2007 onwards was transformed into the original 276 municipality units to allow for a consistent classification of the degree of urbanization at place of residence throughout the study period.…”

Inverse association between urbanicity and treatment resistance in schizophrenia

“…This finding was invariant to the definition used for urban exposure (population size or density); whether urbanicity was determined at birth, upbringing, schizophrenia diagnosis, or interview; and whether based on cohort or cross-sectional study designs (March et al, 2008;Pedersen, 2006Pedersen, , 2015Pedersen and Mortensen, 2001a;Torrey et al, 1997).…”

Delay in blood sampling for routine newborn screening is associated with increased risk of schizophrenia

“…Also, it is reassuring that the effect sizes regarding history of mental illness in a parent (Dean et al, 2010;Mortensen et al, 1999;Pedersen and Mortensen, 2001b), urban birth (Pedersen and Mortensen, 2001b;Pedersen, 2006), obstetric factors (Byrne et al, 2007), and parental age at time of child's birth (McGrath et al, 2014;El-Saadi et al, 2004;Petersen et al, 2011) resemble those for the total Danish population. It provides suggestive evidence that the sample selected from the Danish neonatal Screening Biobank represent an unbiased sample of the Danish population.…”