A hidden link between impulsivity and obesity may not be fixed in human biology but shaped by the cities we live in.
Using a novel engineering-based approach, researchers from NYU Tandon School of Engineering and Italy’s Istituto Superiore di Sanità found that attention-deficit/hyperactivity disorder (ADHD) contributes to obesity not only directly through known biological pathways but also indirectly, by reducing physical activity. The findings are published in PLOS Complex Systems.
Obesity prevalence is also influenced by other city-level variables, such as access to mental health services and food insecurity, thereby opening the door to potential mitigation strategies.
To uncover the nexus between ADHD and obesity, the research team applied urban scaling laws — a mathematical framework from complexity science — to public health data from 915 U.S. cities. Urban scaling describes how features of cities change with population size, similar to how biological traits scale with body size.
They found that both ADHD and obesity decrease sublinearly with population: as cities grow, per-capita prevalence declines. Meanwhile, access to mental health providers and college education rises superlinearly, increasing faster than city size. Larger cities, it seems, offer not just more services, but disproportionately more support for conditions linked to impulsivity.
But size alone doesn’t tell the full story. To reveal where cities over- or underperform relative to expectations, the researchers used Scale-Adjusted Metropolitan Indicators (SAMIs). SAMIs measure how much a city deviates from what urban scaling would predict — highlighting, for example, when a small city has unusually low obesity rates or when a large one falls short on mental health access. These deviations became the foundation for a causal analysis.
“Urban scaling and causal discovery methods allow us to see relationships that traditional health research might miss,” explains Maurizio Porfiri, senior author on the PLOS paper. Porfiri is an NYU Tandon Institute Professor with appointments in the Departments of Mechanical and Aerospace Engineering, Biomedical Engineering, Civil and Urban Engineering, and Technology Management and Innovation. He also serves as Director of the NYU Center for Urban Science + Progress (CUSP).
“Without accounting for how city size naturally affects health metrics, we’d misattribute success or failure to the wrong factors. By filtering out these population effects first, we can identify the true causal pathways linking ADHD to obesity — and more importantly, how urban environments modify these relationships,” adds Tian Gan, Ph.D. student in Mechanical Engineering at NYU Tandon. Simone Macrì, senior scientist at the Istituto Superiore di Sanità in Rome, further comments that “This approach reveals precise intervention points that wouldn’t be apparent otherwise”
Using SAMIs, the team mapped a network of interrelated variables: ADHD prevalence led to higher physical inactivity, which in turn increased obesity. Access to mental health care helped reduce inactivity, indirectly lowering obesity risk. Higher prevalence of college education correlated with better mental health access and more physical activity.
This causal map revealed a dynamic system in which impulsivity, health behaviors, and urban infrastructure interact — and cities themselves either reinforce or weaken these effects.
These patterns weren’t uniform. When the researchers mapped SAMIs by region, cities in the Southeastern and Southwestern U.S. consistently showed greater disparities. Neighboring cities often displayed striking differences in ADHD and obesity prevalence, mental health access, and food insecurity — suggesting that local policy, culture, and resources may either amplify or buffer these behavioral health risks.
“Regional averages can mask a lot of variation,” Porfiri said. “The SAMIs let us see which cities are punching above or below their weight. It’s not just about how big a city is — it’s about how it uses its resources. With this kind of insight, policymakers can target investments in mental health care, education, and physical activity to break the link between ADHD and obesity where it’s strongest.”
To validate the findings at a more granular level, the team analyzed data from over 19,000 children across the U.S. from the National Survey of Children’s Health. The same causal patterns held: children with more severe ADHD were more likely to be obese, especially when physical activity and household education were low.
The study follows earlier work by Porfiri and collaborators using urban scaling to explore firearm ownership and gun violence across U.S. cities. That research revealed that New York City, despite its large size, significantly outperforms expectations on public safety — underscoring how city-level deviations can challenge assumptions about scale and risk.
In addition to Porfiri, Gan, and Macrì, Rayan Succar, a doctoral candidate in Mechanical Engineering working under Porfiri’s advisement, is also an author on the paper.
The research was supported by funding from the U.S. National Science Foundation and the European Union’s Horizon 2020 programme.
