Much greater risk of mental disorders in children of low-income parents
Children of parents with the lowest income are three to four times more likely to be diagnosed with mental illness, compared to children of the very richest parents, according to a study from the Norwegian Institute of Public Health.
The new results reveal large differences in mental disorders in children, and the differences were greater for boys than girls.
– The large differences in mental disorders according to parents' income are startling, especially considering that the income differences in Norway are relatively small compared to other countries, says Jonas Minet Kinge, researcher at the Centre for Fertility and Health, a Centre of Excellence at the Norwegian Institute of Public Health and associate professor of health economics at the University of Oslo.
The researchers found that the diagnosis of ADHD contributed most to the differences in mental disorders, followed by anxiety and depression among children and adolescents. Nevertheless, all mental disorders were higher among children with low-income parents, compared with children from high-income families. The exception was eating disorders in girls, which had no connection with parents' income.
This is the first time that the prevalence of mental disorders among children has been calculated for such detailed income groups in Norway and then analysed to study potential explanatory mechanisms. It is also the first study to analyse subgroups, such as international adoptees, to examine differences in mental disorders according to the adoptive parents' income.
The results from the study show the following when we compare the richest 1% and the poorest 1% of children, based on the parents' income:
Mental disorders were most prevalent among boys with parents in the bottom of the income distribution. In this group, 15.4% were diagnosed with mental disorders. These boys had more than four times as high a proportion diagnosed with mental disorders compared with the boys from the households with the highest income (Figure 1).
The lowest prevalence of mental disorders was found among girls with the richest parents. In this group, 2.8% were diagnosed with mental disorders. At the other end of the scale, girls with poor parents had an incidence of 11.4%.
ADHD, anxiety and depression explain most of the differences
This study confirms previous findings about the relationship between children's mental disorders and parents' income. The recently published study by Kinge and colleagues is one of the few studies that includes a wider range of mental disorders in the analysis. The researchers found that the diagnosis of ADHD contributed most to the differences in mental disorders, followed by anxiety and depression among children and adolescents (Figure 2).
There may be several explanations
Among the most important factors that can explain the differences in mental disorders in children and adolescents, the researchers point out:
- whether the parents have mental disorders themselves
- socio-demographic factors, such as parents' education and whether the household consists of one or two parents
- the children's age
- municipal income inequality
The researchers have conducted several sub-studies to investigate whether these factors could explain the differences in mental disorders in children and adolescents. The answers confirm previous findings that whether children grow up with one or two parents, the parents' level of education in addition to mental disorders in parents are all factors that have a clear connection with the prevalence of mental disorders in children.
– It is also more common for children from low-income households to grow up with single parents, parents with low education and parents with mental illness. In that sense, these factors can contribute to the differences we observe by income, Kinge says.
The researchers also found that the differences in the incidence of mental disorders according to parents' income were greater for older children, compared with younger children.
Social factors come into play
The researchers also performed an analysis only on children adopted abroad, i.e. families where children and parents are not genetically related to each other. Such analyses may account for genetics, which can affect both mental disorders and income. They found a greater proportion of mental disorders in adopted children living in low-income families than in high-income families.
– The connection between parents' income and mental disorders in adopted children supports the hypothesis that a part of the background for mental disorders in children and young people is due to social factors. But the associations were clearly lower than in the general population, Kinge explains.
Nevertheless, Kinge emphasises that this study cannot conclude that low income causes mental illness. Low-income families often have other challenges at the same time.
– Studies from Sweden and other countries indicate that it is not the money itself that casually affect mental disorders in children of parents. For example, access to health information, fetal origins, upbringing and other environmental conditions may explain our findings, Kinge says.
– We need more research on the causes. Fortunately, we have a research community in Norway that has the expertise to link large register data that can be used to conduct detailed analyses, as this study also shows, Kinge concludes.
About the study
The study included 1,354,393 children from 5 to 17 years in the period 2008–2016.
The mean age in the study was 11.2 years.
The family's income was defined as the sum of both parents' income, after tax and adjusted for inflation using the Norwegian consumer price index.
Income data is obtained from tax registers and included wage income, income in connection with self-employment, capital income, pensions and government assistance such as disability benefits.
Data on diagnosed mental disorders are obtained from KUHR (Control and payment of health reimbursements) and the Norwegian Patient Register (NPR) and include reimbursement data from the primary and specialist health services.
Percentages for parents' income
1st percentile: 99 percent of parents have a higher income
25th percentile: 25% have lower income
The 99th percentile: 99 percent have a higher income and 1 percent have a lower one