Mental disorders were 3- to 4-fold more prevalent in children with parents in the lowest income percentiles; parents’ own mental disorders, other socio-demographic factors etc. did not fully explain these associations

Parental income and mental disorders in children and adolescents: prospective register-based study. Jonas Minet Kinge et al. International Journal of Epidemiology, dyab066, May 11 2021. https://doi.org/10.1093/ije/dyab066

Abstract

Background: Children with low-income parents have a higher risk of mental disorders, although it is unclear whether other parental characteristics or genetic confounding explain these associations and whether it is true for all mental disorders.

Methods: In this registry-based study of all children in Norway (n = 1 354 393) aged 5–17 years from 2008 to 2016, we examined whether parental income was associated with childhood diagnoses of mental disorders identified through national registries from primary healthcare, hospitalizations and specialist outpatient services.

Results: There were substantial differences in mental disorders by parental income, except for eating disorders in girls. In the bottom 1% of parental income, 16.9% [95% confidence interval (CI): 15.6, 18.3] of boys had a mental disorder compared with 4.1% (95% CI: 3.3, 4.8) in the top 1%. Among girls, there were 14.2% (95% CI: 12.9, 15.5) in the lowest, compared with 3.2% (95% CI: 2.5, 3.9) in the highest parental-income percentile. Differences were mainly attributable to attention-deficit hyperactivity disorder in boys and anxiety and depression in girls. There were more mental disorders in children whose parents had mental disorders or low education, or lived in separate households. Still, parental income remained associated with children’s mental disorders after accounting for parents’ mental disorders and other factors, and associations were also present among adopted children.

Conclusions: Mental disorders were 3- to 4-fold more prevalent in children with parents in the lowest compared with the highest income percentiles. Parents’ own mental disorders, other socio-demographic factors and genetic confounding did not fully explain these associations.

Keywords: Mental disorders, income, inequality, childhood, adolescence

Key Messages

- Mental disorders in children decreased continuously with increasing parental income for all mental disorders, except eating disorders.

- The parental-income gradient was largest for attention-deficit hyperactivity disorder, followed by anxiety and depression.

- Our study suggests that associations between lower parental income and children’s mental disorders were partly, but not fully, attributed to other socio-demographic factors, parents’ own mental disorders and genetic factors.

Discussion

Three major conclusions can be drawn from this study. First, despite relatively equal access to health services, childhood mental disorders were found to decrease continuously with parental income and there was no dividing line above or below which additional income was no longer associated with mental disorders. The associations varied with child age and sex. Second, the association with parental income was present for all mental disorders except eating disorders and largest for ADHD. Third, the association of parental income with mental disorders could partly, but not fully, be attributed to parental mental disorder and socio-demographic factors. In addition, the associations were present, but less pronounced, in children genetically unrelated to their parents.

Association of parental income and mental disorders by sex and age

The observed patterns of association and sex differences are similar to those of differential life expectancy by income in adults aged ≥40 years in Norway.18 This supports the suggested link between childhood family income and the subsequent socio-economic inequalities in health in adults.33

Association of parental income and subcategories of mental disorders

Previous studies have found associations between parental income and selected mental disorders in children.1 However, studies covering a range of categories are lacking. This study found that the most pronounced associations with parental income were for ADHD in both boys and girls. The prevalence of eating disorders did not vary with parental income in girls. Although varying associations were detected, these findings may be related to the pervasive co-morbidity within mental disorders.34

Evaluation of factors associated with differences in mental disorders by parental income

This study replicates previous findings that one-parent households, low parental education and mental disorders in parents are factors associated with children’s mental disorders.1,35,36 Further, the results show that absolute differences in mental disorders by single-parent household status, parental education and parental mental disorders were greater in children with parents at lower income levels.

Associations between parental income and children’s mental disorders were attenuated when adjusted for household and parental characteristics such as age, education, employment status, mental disorders and one-parent household. Nonetheless, adjusted parental income remained an independent predictor for mental disorders in children, which is in line with previous findings.3

The influence of a genetic component is also suggested. Children of parents with mental illness are at a higher genetic and environmental risk of developing psychopathology.37,38 Low income can be a consequence of psychopathology in parents.37 The largest income difference was found for ADHD, a mental disorder with a strong heritable component, which is also associated with reduced income in adulthood.38 In contrast, the difference across the income spectrum was smaller for anxiety, which has been shown to have a large environmental component.38 These differences suggest confounding by underlying genetic susceptibility on the relationship between parental income and offspring mental disorders. In addition, the associations between parental income and mental disorders in adopted children were weaker compared with children living with their biological parents. The differences in the associations with parental income observed among adopted children and Norwegian-born children were also greater for ADHD than for anxiety disorders.

Although weaker than in children living with their biological parents, the statistically significant associations between parental income and mental disorders in adopted children support that at least some mental health problems are a result of social factors.3

Studies from other countries suggest that registries do not fully capture interview-based diagnoses in children from lower-income families.11 If parental income is associated with use of health services for mental disorders given equal need, diagnoses from health registries could be biased indicators of income gradients in mental disorders. To explore this, we conducted supplementary analyses of the association between psychological-distress score, from the SHLC Survey,17 and health service. This analysis did not suggest that this bias the estimates for Norway.

Also, a strength of our study was that we used primary-care data in addition to specialist-care data, whilst most prior studies have included only specialist services.5 Furthermore, comparisons of diagnostic data from the Composite International Diagnostic Interview with health registry diagnoses on major depressive and anxiety disorders in Norway have been published previously.8 As indicators, registry-based diagnoses have moderate sensitivity and excellent specificity, with 0.2–4.2% false positives.8 The health survey and registry data used in this study have been found to measure the same symptoms.8

This study has some limitations. First, as the diagnoses of mental disorders in children were obtained from health registries, information was only available for individuals in contact with health services. Individuals with less severe cases of depressive disorders and anxiety do not all seek care.8,39 Thus, children with mild or transient symptoms may be underrepresented. Second, primary and specialist healthcare use different standards of diagnostic codes. ICPC2, used in primary care, relies on broader diagnostic categories than the ICD-10 used in specialist care. Thus, some specific mental disorders, such as those in the autism spectrum, do not have specific codes in the primary-care database. In Norway, however, children with autism and other severe conditions are unlikely to not have been under specialist care during the study period. Third, particularities of the setting and potential non-random assignment of adopted children to adoptive parents can affect the interpretation of data on the association between income and mental disorders in adopted children (Part II in the Supplementary Material, available as Supplementary data at IJE online).