Explaining the Association Between Urbanicity and Psychotic-Like Experiences in Pre-Adolescence: The Indirect Effect of Urban Exposures

Abstract

Urban living is a growing worldwide phenomenon with more than two-thirds of people expected to live in cities by 2050. Although there are many benefits to living in an urban environment, urbanicity has also been associated with deleterious health outcomes, including increased risk for psychotic outcomes particularly when the urban exposure occurs in pre-adolescence. However, the mechanisms underlying this association is unclear. Here, we utilize one-year follow-up data from a large (N=7,979), nationwide study of pre-adolescence in the United States to clarify why urbanicity (i.e., census-tract population density) might impact psychotic-like experiences (PLE) by looking at the indirect effect of eight candidate urbanicity-related physical (e.g., pollution) and social (e.g., poverty) exposures. Consistent with other work, we found that of the evaluated exposures related to urbanicity, several were also related to increased number of PLE: PM2.5, proximity to roads, census-level homes at-risk for exposure to lead paint, census-level poverty, and census-level income-disparity. These same urban-related exposures were also related to the persistence of PLE after 1 year, but not new onset of PLE. Mediation analysis revealed that a substantial proportion the urbanicity-PLE association (number and persistence) could be explained by PM2.5 (23–44%), families in poverty (68–93%), and income disparity (67–80%). Together, these findings suggest that specific urban-related exposures contribute to the existence and maintenance, but not onset of PLE, which might help to explain why those in urban environments are disproportionately at-risk for psychosis and point toward areas for public health intervention.

Bane or boon regarding urbanicity and psychotic spectrum disorders: a scoping review of current evidence

“…However, studies specific to children and adolescents reported opposite effects, in that living in an urban area was associated with more PE in children [23 ▪ ] and adolescents [11 ▪ ,12 ▪ ,30 ▪ ], especially for boys [30 ▪ ]. Urbanicity appeared to be associated specifically with persistence of PE, but not its onset [23 ▪ ].…”

“…Specifically, residents in slum and semi-urban areas were observed to have worse outcomes (higher incidence and more progression of PE) when compared to residents from urban areas [36 ▪ ]. However, studies specific to children and adolescents reported opposite effects, in that living in an urban area was associated with more PE in children [23 ▪ ] and adolescents [11 ▪ ,12 ▪ ,30 ▪ ], especially for boys [30 ▪ ]. Urbanicity appeared to be associated specifically with persistence of PE, but not its onset [23 ▪ ].…”

“…Of note, high overnight temperatures linked to the urban heat island phenomena (where there are warmer urban centres as compared to the surrounding rural regions) was associated with risk for hospitalization in schizophrenia patients [35]. High noise [30 ▪ ], air [12 ▪ ,22 ▪▪ ,23 ▪ ] and night-time light [33] pollution levels were features of the urban environment directly or indirectly associated with increased risk of psychosis and PE.…”

“…The most commonly cited definition of an urban area was based on census or administrative data and classification [11 ▪ –14 ▪ ,15,16 ▪▪ ,17,18 ▪ ,19 ▪ ]. Population density [11 ▪ ,13 ▪ ,20 ▪ ,21 ▪ ,22 ▪▪ ,23 ▪ ,24 ▪ ] and population size in a specific area [13 ▪ ,19 ▪ ,25 ▪ –29 ▪ ] were also common parameters used to delineate the urban-rural divide. Other related parameters included settlement size [11 ▪ ] and dwelling density [11 ▪ ,30 ▪ ], percentage of flats and apartments [20 ▪ ,31 ▪▪ ], and the age of such places of dwelling [31 ▪▪ ].…”

“…Four studies focused on patients with first-episode psychosis (FEP) or schizophrenia (FES) [18 ▪ ,25 ▪ ,26 ▪ ,29 ▪ ], one study on patients with chronic high risk of psychosis [27 ▪ ], and one study focused on both FEP and at-risk mental state individuals [40 ▪▪ ]. Five studies were conducted on individuals with psychotic-like experiences (PE) [11 ▪ ,12 ▪ ,23 ▪ ,30 ▪ ,36 ▪ ].…”