A new study from the University Hospital of Geneva (HUG) and the University of Geneva (UNIGE) sheds light on a potentially important link between attention deficit hyperactivity disorder (ADHD) and dementia, identifying common neurobiological markers between the two conditions.
The research, published in Psychiatry and Clinical Neurosciences, showed that adults diagnosed with ADHD have elevated iron levels in specific brain regions, as well as higher concentrations of neurofibrillary tangles (NfL) in their blood. These biomarkers have already been linked to neurodegenerative diseases of old age, such as Alzheimer’s disease. These findings strengthen the hypothesis that ADHD may not simply be a childhood neurodevelopmental disorder, but may be associated with long-term effects on brain health.
«Recent epidemiological studies have suggested an increased risk of dementia in adults with a history of ADHD, but the neurological mechanisms underlying this association remain unclear. Our new findings provide the first neurobiological evidence for a possible common pathogenetic mechanism. “, explains Dr. Paul G. Unschuld, head of the HUG’s Geriatric Psychiatry Department and associate professor of Psychiatry at the UNIGE School of Medicine, who led the study.
ADHD affects approximately 3.5% of adults worldwide, according to estimates by the World Health Organization, and is characterized by persistent difficulties in attention, impulsivity and, in many cases, hyperactivity. Although symptoms appear in childhood, they often continue into adulthood, affecting daily functioning and quality of life.
In contrast, age-related dementias currently affect approximately 55 million people worldwide, with nearly 10 million new diagnoses each year, according to WHO data for 2023. Alzheimer’s disease is the most common form, accounting for 60-70% of cases.
The research team used an advanced neuroimaging technique, quantitative susceptibility mapping (QSM) using magnetic resonance imaging (MRI), to examine brain iron content. The study involved 32 adults with diagnosed ADHD, aged 25 to 45, as well as 29 healthy adults of the same age group as a control group. In addition, levels of the protein neurofibrillary light chain (NfL) were measured in the blood of all participants.
The results showed significant differences in the distribution of iron in specific brain regions of individuals with ADHD compared to healthy participants. Particularly significant was the positive correlation found between iron levels in the premotor cortex and NfL levels in blood plasma.
Iron is essential for proper brain function. However, excessive iron accumulation has been linked to oxidative stress, which can lead to neuronal damage and contribute to the development of neurodegenerative diseases, such as Alzheimer’s disease. ” Increased iron concentrations in specific brain regions are often accompanied by increased oxidative stress, which enhances the process of neuronal degeneration ,” notes Dr. Unschuld.
In contrast, the presence of the NfL protein in the blood is considered an established biomarker of neuronal damage, particularly damage to axons, the structures that allow the transmission of nerve signals. Increased plasma NfL levels indicate underlying neuronal dysfunction or destruction. The simultaneous presence of elevated levels of both iron and NfL in adults with ADHD suggests the possible existence of a neurodegenerative process.
The study findings do not simply reveal a possible link between ADHD and increased dementia risk. Rather, they open new research avenues for understanding the pathogenetic mechanisms that may link these two conditions, providing valuable information for future prevention and treatment strategies.
Dr. Unschuld emphasizes that the data provided by the study “ will contribute to the development of targeted prevention strategies to reduce the risk of dementia in people with ADHD .” This need becomes even more urgent, given the already documented relationship between lifestyle and brain iron accumulation, a factor that appears to play a decisive role.
Furthermore, he notes that further longitudinal studies are needed to investigate whether regulating or reducing brain iron levels could be an effective therapeutic intervention to prevent or slow the onset of dementia in people with a history of ADHD.
