The association between ADHD and obesity: an intriguing puzzle

ADHD often conjures up images of people who can’t sit still. Unsurprisingly, clinicians have argued that the association between ADHD and obesity is counterintuitive – surely people who are more active are less likely to be obese because they are so active. But what does research say?

Samuele Cortese’s (2019) recent review helps us to better understand the relationship between ADHD and obesity. He examined the evidence from available systematic reviews on this topic as well as recent empirical quantitative studies. To save you some time, we’ve summarized his findings (as well as some other recent research) below.

What is the evidence supporting a significant association between ADHD and obesity?

Cortese et al., (2016) and Nigg et al., (2016) found a significant association between ADHD and being overweight. Both studies agree that the relationship between ADHD and obesity is more significant in adults compared to children and adolescents. Nigg and his colleagues, however, found a stronger association in females. A similar study found that, when taking the different ADHD presentations into account (primarily inattentive, primarily hyperactive and so on), the association between higher body mass index (BMI) and the inattentive presentation of ADHD was stronger in females compared to males. Hyperactive and impulsive presentations of ADHD on the other hand were associated with higher BMI in both sexes.

These studies do have a couple of limitations. For example, they did not take the effect of other psychiatric comorbidities associated with ADHD into account (e.g. other conditions that may co-exist alongside ADHD such as learning disabilities, anxiety or depression). Thus, future studies should explore the link of ADHD and obesity while taking these comorbidities into account.

Is there a link between ADHD and obesity?

According to Cortese’s 2019 review, ADHD leads and contributes to obesity. Obesity also leads to ADHD symptoms. This may be partly because the two disorders share common physiological mechanisms. Additionally, they found that there are other underlying factors that contribute to this association.

For instance, a longitudinal study (Cortese et al., 2013) followed individuals diagnosed with ADHD in childhood for 33 years. It found that individuals with childhood ADHD had significantly higher BMI and obesity rates than those without childhood ADHD. However, this study did not have any measure of baseline weight and height. Khalife et al., 2014, followed a sample of children until the age of 16 in which their weight and height were measured with parental reports. They found that teacher-reported ADHD symptoms in childhood predicted adolescent obesity. More specifically, symptoms of inattention and hyperactivity at age 8 were significantly associated with obesity at 16 years of age.

However, similar to Cortese’s study, this study did not directly measure weight and height and it did not assess for a formal diagnosis of ADHD. Aguirre Castaneda et al. (2016) partly addressed this limitation in a follow up study and found that, compared to controls, cases with a formal diagnosis of ADHD were more likely to be overweight.

Nevertheless, the causal association between ADHD and obesity remains unclear. Although several studies suggesting that ADHD precedes and possibly contributes to obesity, a recent study had different findings. Martins-Silva et al., (2019) conducted a linear regression analysis and found a positive causal effect of BMI on ADHD – where ADHD was associated with a lower BMI.

What are the implications of the link between ADHD and obesity for the treatment/management of both conditions?

In conclusion, the relationship between ADHD and obesity is well established, at least in adults. Growing evidence is also being published on the genetic and environmental factors underlying the association. Yet, the specific factors related to the cause-effect links and how the treatment of ADHD impacts obesity outcomes require further investigation. Further research in this field, including other somatic conditions, will provide more rigorous evidence to inform clinical decision-making when treating patients with co-existing ADHD and obesity.