ADHD, asthma, and economic hardship: New research suggests a causal pathway

In a recent study conducted published in npj Mental Health Research, researchers found significant associations between family income, asthma, and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms in children. The findings provide evidence for a causal pathway where lower family income not only directly leads to more severe ADHD symptoms but also has an indirect effect through asthma in early childhood. This research highlights the interconnected nature of socioeconomic status, physical health, and mental health in children.

ADHD is a neurodevelopmental disorder characterized by patterns of inattention, hyperactivity, and impulsivity that are inconsistent with a person’s developmental level. These behaviors interfere with an individual’s functioning or development, affecting various aspects of life, including school performance, interpersonal relationships, and work efficiency. ADHD is commonly diagnosed in childhood and often persists into adulthood.

Prior studies have indicated a potential link between asthma and ADHD, suggesting that inflammatory processes could underlie both conditions. Additionally, both asthma and ADHD are more prevalent in children from lower SES backgrounds, which could suggest a socio-economic component to these conditions. However, the nature of the relationship between ADHD, asthma, and socioeconomic factors remained unclear, prompting researchers to explore potential causal pathways.

“As an economist lately working on child health and socioeconomic disadvantage, I wanted to explore how socioeconomic disadvantage affect child mental and physical health, and if there was any interlinkage between mental and physical health,” said study author Makiko Omura, a professor of economics at Meiji Gakuin University in Tokyo.

For their study, the researchers analyzed data collected from the French EDEN cohort study, initiated in 2003, to investigate the long-term health and developmental outcomes in children, from prenatal stages to childhood. This cohort comprised individuals recruited from prenatal clinics in Poitiers and Nancy, France, where women were enrolled before the 24th week of pregnancy. The EDEN cohort initially included 2,002 women, from which the number of participating mother-child pairs decreased over time, with 1,527, 1,255, and 883 pairs remaining when the children were aged 3, 5, and 8 years, respectively.

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Family income was measured when the child was three years old, categorized into seven ranges, and treated as a continuous variable for analysis. This approach allowed the researchers to examine more nuanced effects of income variations on health outcomes. Asthma status at age three was determined based on parental reports, including criteria such as doctor-diagnosed asthma, use of asthma medication, and instances of wheezing in the past 12 months.

ADHD symptoms were assessed using the Strengths and Difficulties Questionnaire (SDQ) at ages five and eight. The SDQ is a behavioral screening tool that measures various dimensions of child behavior, including inattention and hyperactivity, which are indicative of ADHD.

The study employed a mix of cross-sectional and longitudinal analyses to explore the relationships among the variables at different child ages. The key methodological tool was causal mediation analysis, which allows researchers to differentiate between the direct effects of an exposure (in this case, family income) on an outcome (ADHD symptoms) and the indirect effects mediated through another variable (asthma).

The analysis showed a clear negative association between family income and ADHD symptoms, suggesting that higher family incomes are associated with fewer ADHD symptoms in children. This relationship was both direct and also mediated indirectly through asthma. Specifically, children from lower-income families were more likely to exhibit asthma symptoms by age three, which in turn was linked to higher ADHD symptoms at ages five and eight.

The longitudinal data from the EDEN cohort provided the temporal sequences necessary for establishing causality, suggesting that the onset of asthma influenced the development of ADHD symptoms rather than the other way around. This insight is crucial for developing preventive and intervention strategies that could potentially mitigate ADHD symptoms by managing asthma early in life.

“This study emphasises the complexity of ADHD as a neurodevelopmental condition influenced by a variety of factors, particularly socioeconomic conditions and to some extent physical health, underscoring the need for comprehensive approaches in addressing these challenges,” Omura told PsyPost.

But the study, like all research, includes some caveats.

“The study’s findings are based on a French cohort, which could be limiting the generalizability to other populations with different socioeconomic and health dynamics,” Omura noted. “The absence of genetic and immunological data might overlook key factors influencing both socioeconomic status and mental/physical health conditions. Despite these limitations, the research highlights the significant interplay between socioeconomic factors and child health, underscoring the importance of holistic approaches in public health and policy-making.”

Future research could focus on verifying these findings in other population cohorts and exploring other possible mediators such as environmental triggers or genetic factors. In addition, investigating whether early treatment of asthma can reduce the likelihood of ADHD would be an important area of exploration.

By understanding the pathways linking income, asthma, and ADHD, policymakers and healthcare providers can better target interventions to support at-risk children, potentially mitigating ADHD symptoms. “In particular, the long-term goals are to inform targeted, evidence-based policies that can improve both economic and health outcomes for vulnerable populations, so as to break the intergenerational transmission of poverty and associated health disparities,” Omura said.

The study, “Associations between symptoms of attention-deficit hyperactivity disorder, socioeconomic status and asthma in children,” was authored by Makiko Omura, Samuele Cortese, Marion Bailhache, Marie C. Navarro, Maria Melchior, Judith van der Waerden, Barbara Heude, Blandine de Lauzon-Guillain, and Cédric Galera.