Being born in deprived neighborhoods may increase risk for nonaffective psychosis

Individuals born in more deprived neighborhoods may be at increased risk for nonaffective psychosis because of subsequent effects that impact cognitive development, according to results of a prospective cohort study conducted in Sweden and published in JAMA Psychiatry.

“Given strong evidence that nonaffective psychoses have neurodevelopmental antecedents and that a lower premorbid IQ shows a dose-response relationship with subsequent risk [for] nonaffective psychosis, growing up in more urban or deprived environments could possibly lead to neurodevelopmental sequelae that affect IQ and later risk [for] disorder,” Gemma Lewis, PhD, of the division of psychiatry at University College London, and colleagues wrote. “Although IQ is heritable and stable from early adolescence to old age, strong evidence suggests that it is influenced by socioeconomic status and education in early life, which may be affected by fewer resources and educational opportunities in deprived neighborhoods.”

To test whether IQ is a mediator for the association between being born into more densely populated or deprived areas and subsequent nonaffective psychosis, the researchers evaluated a population-based sample of 227,429 men born in Sweden from 1982 to 1988 who were conscripted into military service at age 18 years. Exposures included continuous measures of small area-level population density by persons per square kilometer and socioeconomic deprivation at birth, which was based on area-level criminal, social and unemployment data. The researchers assessed IQ during conscription at age 18 years. Main outcomes and measures included first diagnosis of ICD-10 nonaffective psychosis from age 18 years until Dec. 31, 2016, recorded in Sweden’s National Patient Register.

Of the total participants, 1,596 (0.7%) were diagnosed with nonaffective psychosis. Odds of nonaffective psychosis increased per one standard deviation (SD) increase in population density (OR = 1.07; 95% CI, 1.04-1.14) and deprivation (OR = 1.09; 95% CI, 1.02-1.13) at birth after adjustments for confounders. The researchers reported a negative association between IQ and deprivation after adjustments, with an effect estimate per one SD increase in deprivation of 0.7 points (95% CI, 0.78 to 0.62) but not with population density. Mediation analyses based on the potential outcome framework revealed that IQ mediated 23% (95% CI, 17-49) of the total effect of deprivation on nonaffective psychosis; however, IQ did not modify associations between deprivation or population density and nonaffective psychosis.

“If replicated, our discoveries have the potential to elucidate causal pathways (neurodevelopmental, social and biological) through which deprivation affects different cognitive domains involved in the onset of psychotic disorder,” Lewis and colleagues wrote. “This research could provide new targets for intervention, particularly in deprived communities where strategies to promote cognitive development in children and young people could reduce the disproportionate burden of nonaffective psychoses.”

In a related editorial, Kenneth S. Kendler, MD, of Virginia Institute for Psychiatric and Behavioral Genetics, and Henrik Ohlsson, PhD, of the Center for Primary Health Care Research at Lund University in Malmö, Sweden, highlighted strengths and cautions regarding Lewis and colleagues’ research.

“The measurement of the three key constructs, [neighborhood deprivation], IQ and [nonaffective psychosis], are strong,” they wrote. “The goal of clarifying causal pathways for classic epidemiologic risk factors is a laudable one. Some caution is needed in interpreting their model, which moves from a community-level risk to an individual-level moderator and outcomes. [Although] likely present, the magnitude of the mediational effect of IQ on the [neighborhood deprivation-nonaffective psychosis] association is probably quite modest, and even in this large sample, imprecisely known.” – by Joe Gramigna

Disclosures: Lewis reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures. The editorial authors report no relevant financial disclosures.