Full Breakdown
Genetic Links Between ADHD and Morning Cortisol Levels
11/20/2025, 3:27:03 PM
Overview of the Study
A recent study published in the journal *Psychoneuroendocrinology* explores the intricate genetic connections between Attention-Deficit/Hyperactivity Disorder (ADHD) and morning cortisol levels, the body's primary stress hormone. Researchers from the University of São Paulo and the Federal University of Rio Grande do Sul, alongside collaborators from Denmark, utilized large-scale genetic data to investigate whether a direct causal relationship exists between these two factors. The findings suggest that rather than a straightforward cause-and-effect link, ADHD and cortisol levels share a complex genetic foundation.
Methodology and Key Findings
The researchers employed Mendelian Randomization, a statistical method that uses genetic variants to assess causal relationships while minimizing environmental influences. They analyzed genetic data from over 225,000 individuals with ADHD and more than 25,000 individuals for morning cortisol levels. Their analysis revealed no evidence supporting a direct causal relationship in either direction. Specifically, genetically predicted morning cortisol levels did not increase the likelihood of ADHD, nor did a genetic predisposition for ADHD alter cortisol levels.
Further investigation into pleiotropy—where the same genes influence multiple traits—led to a global genetic correlation analysis that found no significant overall correlation between ADHD and cortisol. However, a more detailed examination identified two specific genomic regions on chromosomes 5 and 22 with distinct associations. The region on chromosome 5 showed a negative correlation, indicating that genetic variants linked to a higher likelihood of ADHD were associated with lower morning cortisol levels. Conversely, the region on chromosome 22 exhibited a positive correlation, where higher ADHD risk was associated with elevated cortisol levels.
Implications of the Findings
The study's results suggest that the relationship between cortisol and ADHD may be mediated by other behavioral conditions, particularly externalizing disorders such as substance use disorder and oppositional defiant disorder. When controlling for these conditions, a lower cortisol polygenic score was associated with ADHD, indicating that the genetic links between cortisol and ADHD are more nuanced than previously thought.
The researchers propose an "inverted U-shaped" model of physiological regulation, positing that optimal functioning occurs at moderate arousal levels, with deviations potentially contributing to ADHD-related traits. This perspective broadens the understanding of ADHD beyond attention deficits to encompass systemic dysregulation.
Limitations and Future Research
The study acknowledges limitations, including the predominance of European ancestry in the genetic datasets, which may affect the generalizability of the findings. Additionally, the clinical sample size for the polygenic score analysis was modest. Future research is encouraged to examine these genetic links in larger, more diverse populations and to integrate genetic data with longitudinal cortisol measurements to further elucidate the biological interplay contributing to ADHD.
Verbatim Quotes
- “This perspective reframes ADHD not just as a disorder of attention, but as a condition involving broader systemic dysregulation.” — Eugenio H. Grevet, Co-Author
The study, titled “Shared biological pathways linking ADHD and cortisol variability are related to externalizing behaviors,” provides a significant contribution to the understanding of ADHD's biological underpinnings and opens avenues for future research in this area.
