Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopment disorder characterized by inattention or hyperactivity–impulsivity, or both. It might seem paradoxical, but many studies indicate that individuals with a diagnosis of ADHD suffer from overweight and obesity. Therefore, it is important to understand the underlying mechanism that put individuals with ADHD at risk for obesity.
Evidence from within-individual study
A systematic review and meta-analysis (1) based on 728,136 individuals from 42 studies, suggested a significant association between ADHD and obesity both in children/adolescents and adults. The pooled prevalence of obesity was increased by about 70% in adults with ADHD and 40% in children with ADHD compared with individuals without ADHD. However, due to the lack of longitudinal and genetically-informative studies, the meta-analysis was unable to explain the exact direction of association and the underlying etiologic mechanisms. There are several potential explanations:
- ADHD causing obesity: The impulsivity and inattention components of ADHD might lead to disordered eating patterns and poor planning lifestyles, and further caused weight gain.
- Obesity causing ADHD: Factors associated with obesity, for example dietary intake, might lead to ADHD-like symptoms through the microbiota-gut-brain axis.
- ADHD and obesity may share etiological factors: ADHD and obesity may share dopaminergic dysfunctions underpinning reward deficiency processing. So the same biological mechanism may lead to both ADHD and obesity. This is difficult to investigate within individuals, but family studies can help to test this hypothesis.
We will further investigate these possibilities in the Eat2beNICE research project by using both perspective cohort study and twin studies.
Evidence from a recent within-family study
Recently, a population-based familial co-aggregation study in Sweden (2) was conducted to explore the role of shared familial risk factors (e.g. genetic variants, family disease history) in the association between ADHD and obesity. They identified 523,237 full siblings born during 1973–2002 for the 472,735 index males in Sweden, and followed them until December 3, 2009. The results suggest that having a sibling with overweight/obesity is a risk factor for ADHD. This makes it likely that biological factors (that are shared between family members) increase the risk for both ADHD and obesity.
Evidence from across-generation study
Given that both ADHD and obesity are highly heritable complex conditions, across-generation studies may also advance the understanding of the link between ADHD and obesity.
A population-based cohort study (3) based on a Swedish nationwide sample of 673,632individuals born during 1992-2004, was performed to explore the association between maternal pre-pregnancy obesity and risk of ADHD in offspring. The sibling-comparison study design was used to test the role of shared familial factors for the potential association. The results suggest that the association between maternal pre-pregnancy obesity and risk of ADHD in offspring might be largely explained by shared familial factors, for example, genetic factors transmitted from mother to child that contribute to both maternal pre-pregnancy obesity and ADHD.
Together, based on previous evidence from various study designs, there is evidence to suggest that the association between ADHD and obesity mainly is caused by shared etiological factors. However, future studies on different population are still needed to further test these findings.
1. Cortese S, Moreira-Maia CR, St Fleur D, Morcillo-Penalver C, Rohde LA, Faraone SV. Association Between ADHD and Obesity: A Systematic Review and Meta-Analysis. The American journal of psychiatry. 2016;173(1):34-43.
2. Chen Q, Kuja-Halkola R, Sjolander A, Serlachius E, Cortese S, Faraone SV, et al. Shared familial risk factors between attention-deficit/hyperactivity disorder and overweight/obesity – a population-based familial coaggregation study in Sweden. J Child Psychol Psychiatry. 2017;58(6):711-8.
3. Chen Q, Sjolander A, Langstrom N, Rodriguez A, Serlachius E, D’Onofrio BM, et al. Maternal pre-pregnancy body mass index and offspring attention deficit hyperactivity disorder: a population-based cohort study using a sibling-comparison design. Int J Epidemiol. 2014;43(1):83-90.