ADHD manifests as high levels of inattention and/or hyperactivity and impulsivity. © Adobe Stock

Attention-deficit hyperactivity disorder (ADHD) affects many children and is often accompanied by other conditions, such as metabolic disorders, asthma and dental caries. However, uncertainties remain as to the chronology of onset of such conditions, particularly when it comes to knowing which are linked with ADHD over time or, on the other hand, which increase the risk of developing ADHD symptoms. Scientists from Inserm and Université de Bordeaux at the Bordeaux Population Health Center in collaboration with teams in the UK, Sweden and Canada have conducted the most comprehensive analysis to date by evaluating temporal links between ADHD symptoms and a wide range of medical conditions. Their findings, published in Lancet Child and Adolescent Health, highlight the importance of the multidisciplinary management of ADHD patients, based on enhanced collaboration between physical and mental healthcare professionals.

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that begins in childhood and is characterised by high levels of inattention and/or hyperactivity and impulsivity. In addition to the difficulties it causes at school and in professional and social life, research has shown that ADHD is associated with various medical comorbidities (metabolic disorders, asthma, obesity, addictions, etc.) and an increased risk of accidental injury.

Nevertheless, the studies published so far in this area presented methodological limitations. With their small patient samples and lack of long-term health follow-up, they were unable to determine the direction of the links observed and the chronology of their onset. In addition, confounding factors such as social health inequalities or medication use were often insufficiently taken into account.

This made it difficult for scientists to answer a certain number of questions: do comorbidities appear before or after the development of ADHD? Are they directly related to it or caused by other factors? Can ADHD be promoted by previous medical conditions? Yet it is understanding the temporal sequences of these different associations that is essential in order to develop appropriate care and prevention strategies for patients.

The team of Cédric Galera, researcher at the Bordeaux Population Health Center (Inserm/Université de Bordeaux) and child psychiatrist, working with UK, Swedish and Canadian teams, therefore decided to analyse the data of more than 2,000 children from the large-scale Quebec Longitudinal Study of Child Development cohort. The children were followed from 5 months to 17 years of age. They were seen multiple times in early childhood (5 months to 5 years of age), middle childhood (6 to 12 years of age) and in adolescence (13 to 17 years of age).

ADHD and other disorders

On these occasions, the children were evaluated on the severity of any ADHD symptoms they had as well as their physical condition (general health, any illnesses, etc.). These data were reported to the researchers by the person who knew the child best in early childhood, by teachers in middle childhood, and by the child itself in adolescence.

Based on these data and taking into account multiple confounding factors, the scientists carried out statistical analyses to measure the associations between presenting ADHD symptoms and developing certain subsequent physical disorders, and conversely, between presenting physical problems in childhood and then developing subsequent ADHD symptoms.

‘This is the most comprehensive analysis evaluating the temporal links between ADHD symptoms and a wide range of medical conditions, including skin problems, infections, injuries, sleep disorders and other chronic diseases. We sought to evaluate the possible longitudinal associations between ADHD symptoms and a wide range of physical conditions, taking into account several confounding factors,’ explains Galera, who is also the first author of the study.

The scientists showed that having ADHD symptoms in early childhood was associated with a high BMI in middle childhood and adolescence, as well as unintentional injuries in adolescence. Conversely, having presented with unintentional injuries in early childhood was associated with subsequent onset of ADHD symptoms in middle childhood and adolescence. Finally, restless legs syndrome in early childhood also increased the risk of ADHD in middle childhood.

‘By shedding light on the links between ADHD and various comorbidities, as well as the timescale at which they occur, our study reinforces the idea that physical and mental health problems are intertwined, and highlights the need for healthcare professionals of all disciplines to work together in a better way. For example, physicians should be able to refer patients to other disciplinary fields as needed. The earlier we intervene, the more we prevent the evolving risks associated with ADHD,’ emphasises Galera.

To go further, the team will continue to focus on these links by studying data collected on young adults between the ages of 20 and 25. In addition, the scientists would also like to carry out similar work using French data, based on the large cohorts set up in the country, such as the French Longitudinal Study of Children (Elfe).

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