The brains of adults with attention deficit hyperactivity disorder (ADHD) show changes similar to those observed in individuals suffering from dementia.
This is the finding of a study conducted by the Geneva University Hospitals (HUG) and the University of Geneva (UNIGE), which reveals that, compared to healthy individuals, patients diagnosed with ADHD have higher iron levels in certain brain regions as well as elevated levels of neurofilaments (NfL) in their blood.
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These indicators are also two precursor markers of age-related dementias, such as Alzheimer's disease. The study confirms that ADHD may be linked to an increased risk of developing dementia later in life and identifies the neurological mechanism for the first time. A significant breakthrough published in the journal
Psychiatry and Clinical Neurosciences.
ADHD is a common neurodevelopmental disorder affecting approximately 3.5% of adults, according to a 2008 study by the World Health Organization (WHO). It is characterized by an inability to sustain attention and inappropriate levels of hyperactivity and impulsivity. Although symptoms typically appear during childhood and significantly impact academic development and social interactions, their effects can persist and negatively influence daily functioning in adulthood.
Iron plays an essential role in normal brain function, but excessive accumulation can lead to neurodegenerative diseases.
Age-related dementias, on the other hand, affect around 55 million people worldwide, with nearly 10 million new cases each year, according to 2023 WHO statistics. Alzheimer's disease accounts for approximately 60 to 70% of dementia cases.
"Recent epidemiological studies show that adults with ADHD have a higher risk of dementia in later life, but the mechanism by which ADHD poses a risk is unknown," explains Prof. Paul Unschuld, head physician of the Geriatric Psychiatry Service at HUG, associate professor at the Department of Psychiatry of the UNIGE Faculty of Medicine, and initiator of the study.
Iron and neurofilaments as indicators
The research team used an advanced brain imaging method, known as quantitative susceptibility mapping (QSM) via magnetic resonance imaging (MRI), to examine the iron content in the brains of 32 adults aged 25 to 45 with ADHD and 29 healthy controls of the same age range.
In parallel, NfL levels were measured in the participants' blood. The study results reveal notable differences in iron distribution across several brain regions in individuals with ADHD. Additionally, a significant association was established between iron levels in the precentral cortex and NfL levels in the blood.
Iron plays an essential role in normal brain function, but excessive accumulation can lead to neurodegenerative diseases, such as Alzheimer's.
"An iron overload in certain brain regions is often observed and is associated with increased oxidative stress, promoting neuronal degeneration," explains Prof. Paul Unschuld. At the same time, NfL is a marker of neuronal integrity, specifically their axons, which are essential for nerve transmission. Elevated NfL levels in the blood therefore reflect axon damage. Thus, increased brain iron and NfL levels may indicate underlying neurodegenerative pathology and a higher risk of dementia.
These findings confirm that a link exists between ADHD and an increased risk of dementia and identify the first mechanistic elements.
Importance of early detection and ADHD management
These discoveries pave the way for new research to understand how ADHD could be a risk factor for dementia. Prof. Paul Unschuld believes that the insights from this study "will help develop targeted prevention strategies to reduce the risk of dementia in individuals with ADHD.
This is particularly important, as there is a well-known correlation between lifestyle and altered iron levels in the brain. For this, additional longitudinal studies are needed to determine whether reducing brain iron levels is a potential treatment pathway to prevent dementia in later life for individuals with ADHD."
Furthermore, the relationship between ADHD and dementia underscores the importance of early detection of these conditions. It also highlights the need for proactive ADHD management in adults, not only to improve quality of life but also to prevent long-term consequences on cognitive health.
This study was funded by a SPARK grant awarded by the Swiss National Science Foundation (SNSF) to Prof. Paul G. Unschuld.