Summary: Study revealed the place in which a person lived at the age of fifteen was a big influence on the risk of developing both affective psychosis (bipolar disorder) and non-affective psychosis (schizophrenia) later in life.
Source: King’s College London
A first-of-its kind study published in Schizophrenia Research looked at how demographic factors might play a different role in the development of non-affective psychosis (e.g. schizophrenia) when compared to affective psychosis (e.g., bipolar disorder).
Previous research has discovered that rates of some severe mental illness conditions known as non-affective psychoses, such as schizophrenia, will vary depending on geographical location.
This contrasts to affective psychoses like bipolar disorder, which have not shown this geographical variation, despite sharing many other features.
This research was built on previous findings from Dr. Peter Schofield looking at the role of the neighborhood in the development of severe mental illness.
The authors wanted to explore this topic further by analyzing medical data for the entire population of Denmark.
Specifically, they looked at the neighborhood that people lived in when they were 15 years old and their subsequent medical history i.e. the probability that people developed either non-affective psychosis (schizophrenia) or affective psychosis (bipolar disorder).
Results showed that where someone lived as a 15-year-old was a big influence on the rates of subsequent conditions for both non-affective and affective psychosis.
This was also observed with specific demographic categories, with ethnic density found to impact the rates of both affective and non-affective psychoses in individuals from ethnic minority backgrounds.
However, these similarities were not seen when analyzing other demographic factors. When looking at the impact of urbanization, an association was only established with non-affective psychosis.
The most urban neighborhoods were associated with a substantial increase in rates of non-affective psychosis compared to less urban neighborhoods, but no comparable difference was found for affective psychosis.
These data could reflect differences in how non-affective and affective psychosis develop, and the authors note that future research on psychotic disorders could benefit from further analysis of the effects of different risk factors on the development of these disorders.
A comparison of neighbourhood level variation and risk factors for affective versus non-affective psychosis
Studies typically highlight area level variation in the incidence of non-affective but not affective psychoses. We compared neighbourhood-level variation for both types of disorder, and the specific effects of neighbourhood urbanicity and ethnic density, using Danish national registry data.
Population based cohort (2,224,464 people) followed from 1980 to 2013 with neighbourhood exposure measured at age 15 and incidence modelled using multilevel Poisson regression.
Neighbourhood variation was similar for both disorders with an adjusted median risk ratio of 1.37 (95% CI 1.34–1.39) for non-affective psychosis and 1.43 (1.38–1.49) for affective psychosis. Associations with neighbourhood urbanicity differed: living in the most compared to the least urban quintile at age 15 was associated with a minimal increase in subsequent affective psychosis, IRR 1.13 (1.01–1.27) but a substantial increase in rates of non-affective psychosis, IRR 1.66 (1.57–1.75). Mixed results were found for neighbourhood ethnic density: for Middle Eastern migrants there was an increased average incidence of both affective, IRR 1.54 (1.19–1.99), and non-affective psychoses, 1.13 (1.04–1.23) associated with each decrease in ethnic density quintile, with a similar pattern for African migrants, but for European migrants ethnic density appeared to be associated with non-affective psychosis only.
While overall variation and the effect of neighbourhood ethnic density were similar for both types of disorder, associations with urbanicity were largely confined to non-affective psychosis. This may reflect differences in aetiological pathways although the mechanism behind these differences remains unknown.