Research has found a link between ADHD, iron in the brain, and dementia risk.
- Attention deficit
hyperactivity disorder (ADHD) is most commonly diagnosed in childhood, but
diagnoses in adults are increasing.
- Adult ADHD is associated
with a higher risk of developing dementia, but experts do not yet know
why.
- A new study has found that
people with ADHD in adulthood have increased iron in regions of their
brain and elevated levels of markers of nerve damage, both of which are
also seen in dementia.
Research
suggests that adults with ADHD have a higher risk of developing
dementia, and the reasons for this are currently unclear. Now, a new study has
supported this link and suggested the neurological mechanisms involved in this
increased risk.
Professor Paul G. Unschuld, head of the Division of Geriatric Psychiatry
of the HUG, associate professor in the Department of Psychiatry at the UNIGE Faculty
of Medicine, and the initiator of the study, explained in a press release why they carried out the research:
“Recent epidemiological
studies show that adults suffering from ADHD have an increased risk of dementia
at an advanced age, but the mechanism through which ADHD constitutes a risk is
not known.”
Their study, published inPsychiatry
and Clinical NeurosciencesTrusted Source, found that adults
with ADHD have increased levels of iron in areas of the brain that are
associated with cognitive functions. They also found blood biomarkers of nerve
damage, similar to those seen in people with dementia.
“The
findings provide an interesting perspective on the long-term neurological
effects of ADHD, but the study’s small sample size (32 ADHD patients) means
broader conclusions should be approached with caution. More longitudinal
research is needed to confirm whether brain iron accumulation and axonal damage
directly increase dementia risk or if other factors (e.g., lifestyle,
medication, genetics) contribute to the observed patterns.”
— Steve Allder, MD, consultant neurologist at Re:Cognition
Health, who was not involved in the study
Examining
iron buildup in the brain
Although iron plays an
essential role in brain functioning, excessive accumulation can cause damage to nerve cells
and immune cells in the brain, leading to neurodegenerative diseases such as
Alzheimer’s. Studies have shown that as we age, iron accumulates in
our brains, and this may be associated with poorer cognitive performance.
For this study, the
researchers recruited 32 adults with a clinical diagnosis of ADHD (aged 20-58
years, mean age 35) and 29 age-matched controls (aged 19-59 years, mean age
32). All participants underwent brain magnetic
resonance imaging (MRI), standardized psychometric testing and
assessment of lifestyle factors, such as smoking and body mass indexTrusted Source (BMI),
that might affect the health of blood vessels in the brain, potentially
increasing dementia risk.
To assess iron
deposition in the brain, the researchers used quantitative
susceptibility mapping (QSM), a form of scanning that can
detect areas of magnetism in the brain.
Marissa Sobolewski, PhD, Assistant professor of Environmental
Medicine and Neuroscience, University of Rochester Medical Center, explained
the importance of this:
“Fe [iron] is critically important for neuronal
myelination and more research is needed to understand how iron overload can
influence neuronal damage, including research on a form of cell death called
ferroptosis. Iron overload is a common phenotype associated with
neurodegenerative disease and an important area for future research focused on
neurodevelopmental disorders like ADHD.”
They also measured neurofilament
light chainTrusted Source (NfL) levels
in the blood plasma, to determine the neuroaxonal integrity — health of the
nerve cells — in the brain. Raised NfL levels in blood plasma indicate damage
to the nerve axons (fibres).
High
brain iron levels, ADHD, and Alzheimer’s
In participants with ADHD, high iron levels were
detected in the precentral cortexTrusted Source —
the area of the brain that controls voluntary movement — the cerebral white matter, which is
responsible for communication between nerve cells to enable cognitive functions
and several other structures in the brain.
“It
is important that we begin to recognize that many diseases and disorders of the
nervous system are co-morbid and share similar mechanisms of injury, like white
matter and neuronal damage. Instead of studying these diseases and disorders in
isolation, we should begin to study risk factors that these disorders share.”
— Marissa Sobolewski
As well as having higher
iron levels than control individuals, those with ADHD had raised NfL levels in
their blood plasma, indicating neuroaxonal damage. Studies have
found that people in the early stages of Alzheimer’s disease have increased
NfL, a biomarker of neurodegenerative brain change, in their cerebrospinal
fluid, as well as in their blood.
Allder explained:
“Iron plays a crucial role in neurotransmitter
synthesis, especially dopamine, which is already known to be dysregulated in
ADHD. However, excess iron can lead to oxidative stress, damaging neurons and
possibly accelerating neurodegeneration.”
“High iron levels can
promote oxidative stress, which may damage neuronal axons. This aligns with the
increased NfL levels found in ADHD patients, which indicate axonal injury,” he
added.
What
are the symptoms of ADHD?
Attention deficit
hyperactivity disorder (ADHD) is a condition usually diagnosed during
childhood, but may continue into, or be diagnosed in adults. In adults, it is
characterized by some or all of the following symptoms:
- Difficulty paying attention, being easily
distracted and interrupting people
- Problems with organization, following
instructions, and completing tasks
- Restlessness and difficulty sitting still
- Forgetfulness
- Easily becoming irritable, impatient, or
frustrated
- Difficulty dealing with stress
- Impulsive behavior.
According to the CDCTrusted Source, experts are still
unsure what causes ADHD, but genetics may play a role, as may maternal exposure
to environmental factors such as lead, alcohol and tobacco during pregnancy,
and head injury.
Studies have
found that people with ADHD may have widespread micro- and macro-structural
differences in their brain from people without this diagnosis.
Could
iron reduction reduce dementia risk?
The authors suggest that
in adult ADHD, there may be a link between excess brain iron and neuroaxonal
vulnerability, possibly mediated by oxidative stress, which could account for
the association between adult ADHD and dementia.
“If ADHD-related brain changes persist into adulthood, the combination of oxidative stress, inflammation and neuroaxonal vulnerability could increase susceptibility to neurodegenerative conditions like Alzheimer’s.”— Steve Allder
The authors acknowledge
limitations in their study, particularly that as a cross-sectional study, it
cannot detect changes in participants over time.
However, Unschuld suggests that their findings might
enable targeted prevention strategies to be developed to reduce the risk of
dementia in persons affected by ADHD.
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