CHPR: Dr. Hedges, please start by telling us about yourself and your background.
Dr. Hedges: I’m a professor of psychology and a faculty member in the neuroscience center at Brigham Young University. My research focuses on cognitive epidemiology and on the influence of environmental variables on cognitive outcomes. My colleagues and I recently reviewed the association across specific psychiatric diagnoses and cognitive function over time (Hedges DW et al, Brain Sci 2024;14:722).

CHPR: How strong is the connection between psychiatric disorders and the risk of developing dementia later in life?
Dr. Hedges: There does appear to be a connection, although it’s a complicated one, and we’re still working out exactly what it means. Large population studies suggest that people with a history of psychiatric illness may be at higher risk for developing dementia later on. For example, a 30-year New Zealand study of more than 1.7 million people found that individuals with a history of mental disorders had about a fourfold greater risk of dementia, and dementia developed on average about 5–6 years earlier than in those without a psychiatric history (Richmond-Rakerd LS et al, JAMA Psychiatry 2022;79:333–340). That association remained significant even after adjusting for factors such as gender, preexisting chronic physical disease, and neighborhood deprivation, suggesting that the link is not explained solely by those general dementia risk factors. The association was seen for both Alzheimer’s disease and other dementias.

“While I would not tell patients that treatment has been proven  to prevent dementia, I do think there is a practical message here: Treating psychiatric illness well, reducing relapse, and improving  overall functioning can support long-term brain health.”
Dawson Hedges, MD

CHPR: Depression seems to get the most research attention in this area. What does the evidence actually show?
Dr. Hedges: Yes, depression has been studied the most. For example, a large Danish nationwide study followed people diagnosed with depression and compared them to individuals without depression (Elser H et al, JAMA Neurol 2023;80:949–958). Overall, people with depression had more than double the risk of developing dementia compared to those without depression. Another interesting finding was that depression diagnosed in early adulthood or midlife was still associated with increased dementia risk decades later. Depression later in life may sometimes be an early manifestation of the underlying neurodegenerative process rather than a risk factor, so interpreting these findings requires some caution.

CHPR: Another complication is that depression itself can affect cognitive functioning.
Dr. Hedges: Right—depression can affect attention, memory, and overall mental efficiency. Because of that, depression-related cognitive symptoms can sometimes resemble early dementia and complicate the evaluation. However, the pattern is often different: Psychiatric disorders tend to affect attention, processing speed, and executive functioning, whereas Alzheimer’s disease typically begins with gradually worsening memory. Another challenge is that both psychiatric disorders and dementias cover a wide range of conditions. Depression can vary widely in symptoms, severity, treatment history, and age of onset, while dementia includes Alzheimer’s disease, vascular dementia, Lewy body dementia, and mixed forms, each with different underlying etiology. On top of that, studies have not always distinguished between dementia subtypes, making the findings harder to interpret.

CHPR: With these limitations in mind, what’s known about dementia risk in other psychiatric disorders?
Dr. Hedges: Bipolar disorder and schizophrenia have also been linked to elevated risk. A large study from Taiwan found that bipolar disorder was associated with about a sevenfold increase in dementia risk (Lin SH et al, Am J Geriatr Psychiatry 2020;28:530–541). In older US adults with schizophrenia, dementia diagnoses were markedly more common and appeared much earlier than in those without serious mental illness: By age 66, about 28% already had a dementia diagnosis compared with 1.3% of those without serious mental illness, and by age 80 the figure was about 70% versus 11% (Stroup TS et al, JAMA Psychiatry 2021;78:632–641). There aren’t as much data for some other disorders, but a few reports suggest there may be an association. One large analysis found that adults with ADHD had nearly a threefold increased risk of dementia, although other research has not found the same pattern (Levine SZ et al, JAMA Netw Open 2023;6(10):e2338088). PTSD has been linked to higher dementia risk in both veterans and civilians, and a Taiwanese longitudinal study found that people with OCD had roughly a fourfold higher risk (Günak MM et al, Br J Psychiatry 2020;217:600–608; Chen MH et al, J Clin Psychiatry 2021;82:20m13644).

CHPR: What might explain the link between psychiatric illness and dementia? Do these disorders directly affect the brain, or do they share underlying biology with dementia?
Dr. Hedges: One possibility is shared genetic or biological vulnerability that increases risk for both conditions (Hirakawa H and Terao T, Front Psychiatry 2024;15:1414776; Tao F et al, PLoS One 2025;20:e0322752). Chronic stress and inflammation might also play a role. Prolonged stress-hormone exposure and increased inflammation can affect brain regions like the hippocampus that are involved in memory. Another concept is cognitive reserve—basically the brain’s ability to tolerate age-related changes while still functioning well. Severe or long-standing psychiatric illness can affect education, work, and social engagement, which may influence that reserve over time (Hedges et al, 2024). Psychiatric disorders can also impact many everyday factors that affect dementia risk, such as physical activity, cardiovascular health, sleep, substance use, and social isolation. There’s also the concept of neuroprogression in bipolar disorder, where repeated mood episodes appear to be associated with gradual changes in brain structure and function over time.

CHPR: That has practical implications too. For patients who are ambivalent about maintenance treatment, it suggests that preventing relapse may also help protect long-term brain health.
Dr. Hedges: Right. And lifestyle factors are very important. The 2024 Lancet Commission on dementia prevention identified several modifiable risk factors, including physical inactivity, smoking, excessive alcohol use, hypertension, high cholesterol, and social isolation (Livingston G et al, Lancet 2024;404:572–628). Psychiatric disorders can worsen many of these risks because they often affect levels of physical activity, sleep, nutrition, medical adherence, social connection, and access to health care. We clinicians can contribute to dementia prevention even without doing anything fancy. Encouraging exercise, improving sleep, addressing substance use, monitoring metabolic health, supporting social engagement, coordinating with primary care, and minimizing anticholinergic burden are all practical steps that matter for long-term cognitive health (Editor’s note: See our interview with Douglas Noordsy, MD, on “The Emerging Field of Lifestyle Psychiatry” in CHPR Jul/Aug/Sep 2024 and with Shelly Gray, PharmD, on “Anticholinergic Drugs and Risk of Cognitive Impairment and Dementia” in CHPR Oct/Nov/Dec 2021).

CHPR: Has treating psychiatric disorders been found to reduce the likelihood of developing dementia down the line?
Dr. Hedges: That is an important question, and the answer right now is: Maybe, but we need more evidence. There are some encouraging signs. In the ADHD cohort study I mentioned, adults with ADHD had increased dementia risk overall, but those who received treatment did not show the same elevated risk (Levine et al, 2023). In bipolar disorder, a greater number of relapses has been associated with higher dementia risk, which raises the possibility that better relapse prevention might protect long-term cognitive health (Lin et al, 2020).

CHPR: And is there similar evidence in depression?
Dr. Hedges: We see similar patterns. For depression, a large cohort study found that individuals receiving treatment had lower dementia risk than those whose depression went untreated (Yang L et al, Biol Psychiatry 2023;93(9):802–809). Another study found that improvement in depressive symptoms from psychotherapy was associated with a lower subsequent dementia risk (John A et al, Psychol Med 2023;53(11):4869–4879). So, while I would not tell patients that treatment has been proven to prevent dementia, I do think there is a practical message here: Treating psychiatric illness well, reducing relapse, and improving overall functioning can support long-term brain health.

CHPR: And in fact, there are some data about lithium having neuroprotective benefits, right?
Dr. Hedges: Yes, but the evidence is mixed. Observational studies suggest that people treated with lithium may have a lower risk of dementia, and there are plausible reasons to think lithium could affect the amyloid and tau pathways involved in Alzheimer’s disease (Chen S et al, PLOS Med 2022;19:e1003941). But randomized trial data are less encouraging. A recent meta-analysis of RCTs in Alzheimer’s dementia found no consistent cognitive or functional benefits (Pereira da Silva AM et al, Am J Geriatr Psychiatry 2026;34(3):371–385). So lithium remains interesting from a brain-health standpoint, but the evidence is not strong enough to use it for dementia prevention or treatment.

CHPR: Are psychiatric diagnoses linked predominantly with any specific type of dementia?
Dr. Hedges: Studies of depression have found it’s more strongly linked to vascular dementia than to Alzheimer’s disease (Elser et al, 2023). For us clinicians, that highlights the importance of paying close attention to vascular risk factors—such as hypertension, diabetes, smoking, and physical inactivity—in patients with depression, especially in midlife and later life. For other psychiatric disorders, such as bipolar disorder or schizophrenia, the increased dementia risk appears to be present across several dementia types, and most studies have not clearly identified a single predominant subtype. A recent study of people with severe, extremely treatment-resistant schizophrenia found that their pattern of cognitive impairment differed from Alzheimer disease, frontotemporal dementia, and Lewy body dementia, raising the possibility that in some patients, the dementia syndrome reflects schizophrenia-related cognitive decline rather than a classic neurodegenerative subtype (Pathak US et al, JAMA Psychiatry 2026; Epub ahead of print).

CHPR: It sounds like we should monitor cognitive function more closely in patients with long-standing psychiatric illness. And it’s also a nudge for us to be proactive about metabolic monitoring rather than leaving the task entirely to primary care.
Dr. Hedges: I think that’s reasonable, especially in patients with severe or recurrent illness, vascular risk factors, multiple hospitalizations, or noticeable functional decline. Most psychiatric guidelines focus, understandably, on symptom reduction, relapse prevention, and safety, but long-term cognitive health is not always front and center, especially in younger or middle-aged adults. Bringing it in doesn’t require a dramatic change in practice. You don’t necessarily need formal neuropsychological testing for everyone, but it helps to have a baseline sense of the patient’s cognitive functioning and whether that is changing over time. That may mean asking about memory, attention, daily functioning, medication management, and work or social performance on a regular basis. What often matters most is the trajectory. Stable cognitive deficits are different from steadily worsening decline. Watching that pattern over time can help us decide when a more formal evaluation is needed.

CHPR: What areas of research are most promising right now when it comes to preventing or delaying dementia in people with psychiatric disorders?
Dr. Hedges: Several areas are getting attention. One is multidomain prevention, meaning interventions that combine exercise, diet, vascular risk reduction, and cognitive or social engagement. There is also growing interest in whether some medications might influence long-term brain health. GLP-1 receptor agonists, which are used for diabetes and obesity, have been associated with lower dementia risk in some studies (Chuansangeam M et al, J Alzheimers Dis Rep 2025;9:25424823251342182). Lithium continues to attract attention because of possible neuroprotective effects. But I would say the most clinically relevant message right now is still the simplest one: Good psychiatric care is part of good brain health care. That includes supporting treatment adherence, preventing relapse, encouraging healthy lifestyle habits, and addressing medical comorbidities.

CHPR: Thank you for your time, Dr. Hedges.