Lower Parental Income in Childhood Associated With Schizophrenia Risk

Children from lower income families have a higher risk for schizophrenia, per study data published in JAMA Psychiatry.

Christian Hakulinen, PhD, from the University of Helsinki in Finland, conducted a national cohort study of all persons born in Denmark from 1980 through 2000. Enrollees were followed from their 15th birthday until schizophrenia diagnosis, emigration, death, or conclusion of follow-up on December 31, 2016.

The main outcome was the hazard ratio (HR) for schizophrenia, estimated by Cox proportional hazard regression, as well as cumulative incidence values, and parental income measured at birth and ages 5, 10, and 15 years was the main exposure. The highest income quintile was used as the reference category. Covariates included history of parental mental disorders, parental educational attainment, urbanization at place of residence, and changes in child-parent separation status from birth to age 15 years.

Of the total analytical cohort (N=1,051,033; 51.3% male), 0.72% (n=7544; 54.7% male) were diagnosed with schizophrenia. Overall, parental income level was inversely associated with risk for schizophrenia, and a dose-response relationship was observed between duration of time spent in lowest income quintile and schizophrenia risk.

Children whose parents remained in the lowest income quintile at birth through age 15 years were at the highest risk for subsequent schizophrenia diagnosis (HR, 4.12; 95% CI, 3.71-4.58). Notably, for children born in the lowest income quintile who later rose to the second-lowest quintile at age 15 years, the risk for schizophrenia was significantly attenuated (HR, 2.80; 95% CI, 2.46-3.17). Among children born in the most affluent quintile, downward mobility between birth and age 15 years was associated with increased risk for schizophrenia. As such, parental income mobility appeared to be inversely associated with schizophrenia risk.

These relationships were attenuated, but remained significant after adjustments for urbanization, parental mental disorders, parental educational, and separation status. Overall, these data suggest that risk for schizophrenia may be associated with parental income level and income mobility. As a study limitation, authors noted that maximum age of follow-up was 37 years, thus excluding potential later-life cases of schizophrenia.

In a companion editorial published in JAMA Psychiatry, Richard G. Frank, PhD, from Harvard University, Boston, Massachusetts, offered some potential causal pathways for these associations. Although prior research suggests that heritability accounts for 66% to 85% of schizophrenia risk, additional risk factors include stress and the “nature of caregiving,” or the home environment and caregiver conduct. Low income levels are associated with difficult living conditions and can restrict resources available for childcare.

In addition to interventions that address income inequality and poverty, Dr Frank wrote that “providing child care, early education, and parenting supports may be effective in reducing the onset of schizophrenia” among high-risk children.

Reference

1. Hakulinen C, Webb RT, Pedersen CB, Agerbo E, Mok PLH. Association between parental income during childhood and risk of schizophrenia later in life [published online October 23, 2019]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2019.2299
2. Frank RG. Reflections on the link between income during childhood and risk of developing schizophrenia [published online October 23, 2019]. JAMA Psychiatry. doi:10.1001/jamapsychiatry.2019.2968