Importance: 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.
Objective: 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 1980-2000, followed up from 15th birthday until schizophrenia diagnosis, emigration, death, or December 2016, whichever came first.
Exposures: Parental income measured during birth-year and at ages 5, 10 and 15 years.
Main outcome measures: Hazard ratios (HRs) for schizophrenia were estimated using Cox regression. Cumulative incidence values (absolute risks) were also calculated.
Results: The cohort included 1,051,033 (48.7% females) participants. 7544 (45.3% females) cohort members were diagnosed with schizophrenia during 11.6 million person-years of follow-up. There was an inverse relationship 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 relationship 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 born in and who remained in the lowest income quintile at age 15 had a 4.12 (95% CI 3.71-4.58) fold elevated risk versus 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 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 was associated with increased risks of developing schizophrenia.
Conclusions and relevance: Parental income level, and income mobility, during childhood is linked with schizophrenia risk. Although both causation and selection mechanisms could be involved, enabling upward income mobility could influence schizophrenia incidence at whole population level.