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How are parental income level and income mobility during childhood associated with subsequent risk for schizophrenia?
This Danish cohort study of more than 1 million persons found a dose-response association between increasing amount of time spent in low-income conditions and greater schizophrenia risk. Regardless of parental income level at birth, upward income mobility was associated with lower schizophrenia risk compared with downward mobility.
Although causality cannot be assumed, this study’s findings suggest that enabling upward family income mobility during childhood may reduce subsequent schizophrenia incidence.
Evidence linking parental socioeconomic position and offspring’s schizophrenia risk has been inconsistent, and how risk is associated with parental socioeconomic mobility has not been investigated.
To elucidate the association between parental income level and income mobility during childhood and subsequent schizophrenia risk.
Design, Setting, and Participants
National cohort study of all persons born in Denmark from January 1, 1980, to December 31, 2000, who were followed up from their 15th birthday until schizophrenia diagnosis, emigration, death, or December 31, 2016, whichever came first. Data analyses were from March 2018 to June 2019.
Parental income, measured at birth year and at child ages 5, 10, and 15 years.
Main Outcomes and Measures
Hazard ratios (HRs) for schizophrenia were estimated using Cox proportional hazard regression. Cumulative incidence values (absolute risks) were also calculated.
The cohort included 1 051 033 participants, of whom 51.3% were male. Of the cohort members, 7544 (4124 [54.7%] male) were diagnosed with schizophrenia during 11.6 million person-years of follow-up. There was an inverse association between parental income level and subsequent schizophrenia risk, with children from lower income families having especially elevated risk. Estimates were attenuated, but risk gradients remained after adjustment for urbanization, parental mental disorders, parental educational levels, and number of changes in child-parent separation status. A dose-response association was observed with increasing amount of time spent in low-income conditions being linked with higher schizophrenia risk. Regardless of parental income level at birth, upward income mobility was associated with lower schizophrenia risk compared with downward mobility. For example, children who were born and remained in the lowest income quintile at age 15 years had a 4.12 (95% CI, 3.71-4.58) elevated risk compared with the reference group, those who were born in and remained in the most affluent quintile, but even a rise from the lowest income quintile at birth to second lowest at age 15 years appeared to lessen the risk elevation (HR, 2.80; 95% CI, 2.46-3.17). On the contrary, for those born in the most affluent quintile, downward income mobility between birth and age 15 years was associated with increased risks of developing schizophrenia.
Conclusions and Relevance
This study’s findings suggest that parental income level and income mobility during childhood may be linked with schizophrenia risk. Although both causation and selection mechanisms could be involved, enabling upward income mobility could influence schizophrenia incidence at the population level.
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Accepted for Publication: June 23, 2019.
Corresponding Author: Christian Hakulinen, PhD, Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki, PO Box 21, 00014 Helsinki, Finland (firstname.lastname@example.org).
Published Online: October 23, 2019. doi:10.1001/jamapsychiatry.2019.2299
Author Contributions: Dr Hakulinen had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: All authors.
Acquisition, analysis, or interpretation of data: Hakulinen, Webb, Agerbo, Mok.
Drafting of the manuscript: Hakulinen, Mok.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Hakulinen, Agerbo.
Obtained funding: Hakulinen, Webb.
Administrative, technical, or material support: Agerbo.
Supervision: Webb, Pedersen, Agerbo, Mok.
Conflict of Interest Disclosures: None reported.
Funding/Support: This study was supported by the Academy of Finland (grant 310591; Dr Hakulinen), the Stanley Medical Research Institute (Drs Pedersen and Agerbo), the Lundbeck Foundation, Denmark (Drs Pedersen and Agerbo), and the European Research Council (grant 335905; Dr Webb).
Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
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