Alzheimer’s and ADHD, the Missing Link?
Alzheimer’s dementia (AD) is a cognitive disorder characterized, in part, by impulsive behavior and a reduced capacity for sustained attention, memory, organizing, multi-tasking, and completing daily tasks [1, 2]. Attention Deficit Hyperactivity Disorder (ADHD) is a cognitive disorder characterized, in part, by impulsive behavior and a reduced capacity for sustained attention, memory, organizing, multi-tasking, and completing daily tasks [1, 3]. You, dear reader, may notice that these lists are similar. This similarity begs the question: are these two conditions related? There have been a few studies looking at the link between ADHD and Alzheimer’s in the past, but two recent large-scale studies looked at millions of patients to see if there was a link [3, 4].
Before we jump straight to the big studies, a couple of quick asides. First, these studies looked at adult ADHD. ADHD is typically categorized as a neurodevelopmental disorder, a disorder of the brain that begins in childhood. Recent studies have found evidence that childhood onset and adult onset ADHD may be different diseases [5]. A study in New Zealand published in 2015 followed over a thousand participants for 40 years and found that the people who had childhood ADHD and those who had adult ADHD were largely different groups[5]. Specifically, 95% of children with ADHD did not show symptoms by adulthood, and 90% of those with adult ADHD did not show symptoms as a child [5]. More research needs to be done to explore this phenomenon, but as the studies in question used adult ADHD, they make no claims about a link between childhood ADHD and Alzheimer’s dementia. Second, the studies were observational, meaning they did not perform a randomized, controlled experiment. While the enormous size of the populations helps strengthen the observations, they do not substitute for experimental evidence. This means the studies cannot rule out other factors that may influence the associations or confirm whether the associations might work in the opposite direction (i.e., they can’t determine cause and effect).
In a study published in 2023, researchers looked at 109 thousand patient records from Israel over the course of 17 years [4]. The patients they selected were fairly representative of the population as a whole and were, on average, 57 at the start of the study and 75 at the end [4]. They found that those diagnosed with adult ADHD were nearly twice as likely to be diagnosed with dementia by the end [4]. The scientists noted that this finding was stable across all divisions of the population except those who were on ADHD medication, a relatively small section of individuals [4]. A much larger study published in 2022 looked at 3.5 million Swedes over 12 years - a significant portion of the Swedish population [3]. The study looked at records of adults who were, on average, 50 years old at the beginning and 63 by the end. It found that adult ADHD was a significant risk factor for developing dementia and mild cognitive impairment, especially for males [3]. Additionally, the study found that this risk was unaffected by factors such as education level, metabolic conditions, sleep disorders, and developmental disorders. However, the risk was significantly reduced when other psychiatric disorders - such as depression, anxiety, substance use, and bipolar disorder - were taken into account [3].
Does this mean ADHD causes dementia? No! These studies have no ability to tell us the causes and effects. What these studies tell us is that people with ADHD may be at an increased risk of developing dementia and may want to be careful to avoid other risk factors. The real benefit of these studies is that they give us more exciting questions to ask and explore with research. Such as:
- Does ADHD somehow prime the brain to be more vulnerable to dementia?
- Why weren’t those on psychostimulant ADHD medication prone to increased risk?
- Could those medications help protect against dementia?
- Could the people on medications have a more severe form of ADHD, which is somehow protective?
- Is there a brain state that makes it more vulnerable to ADHD, dementia, and other psychiatric disorders?
- What are the underlying brain mechanisms that link ADHD and dementia?
These questions and more are exciting because they may reveal avenues for emerging treatments in the future. High-quality clinical research studies can only take place with the help of willing volunteers like you, dear reader. The most exciting part of science is finding something unknown, even if the genesis of that finding is that two things look very, very similar.
Creative Director Benton Lowey-Ball, BS, BFA
|
Click Below for ENCORE Research Group's Enrolling Studies |
|
|
|
Click Below for Flourish Research's Enrolling Studies |
References:
[1] Callahan, B. L., Bierstone, D., Stuss, D. T., & Black, S. E. (2017). Adult ADHD: risk factor for dementia or phenotypic mimic?. Frontiers in Aging Neuroscience, 9, 260. https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2017.00260/full
[2] Yokoi, T. (2023). Alzheimer’s Disease is a Disorder of Consciousness. Gerontology and Geriatric Medicine, 9, 23337214231159759. https://pmc.ncbi.nlm.nih.gov/articles/PMC9989409/
[3] Dobrosavljevic, M., Zhang, L., Garcia-Argibay, M., Du Rietz, E., Andershed, H., Chang, Z., ... & Larsson, H. (2022). Attention-deficit/hyperactivity disorder as a risk factor for dementia and mild cognitive impairment: A population-based register study. European Psychiatry, 65(1), e3. https://pmc.ncbi.nlm.nih.gov/articles/PMC8792867/
[4] Levine, S. Z., Rotstein, A., Kodesh, A., Sandin, S., Lee, B. K., Weinstein, G., ... & Reichenberg, A. (2023). Adult attention-deficit/hyperactivity disorder and the risk of dementia. JAMA network open, 6(10), e2338088-e2338088. https://pmc.ncbi.nlm.nih.gov/articles/PMC10582792/
[5] Moffitt, T. E., Houts, R., Asherson, P., Belsky, D. W., Corcoran, D. L., Hammerle, M., ... & Caspi, A. (2015). Is adult ADHD a childhood-onset neurodevelopmental disorder? Evidence from a four-decade longitudinal cohort study. American Journal of Psychiatry, 172(10), 967-977. https://psychiatryonline.org/doi/full/10.1176/appi.ajp.2015.14101266
