- A large new study finds an association between mental health conditions and dementia later in life.
- Although research has not established a causal link, mental health problems remain a predictor of dementia.
- Successfully addressing mental health conditions can help reduce the likelihood of dementia in older adults.
As of 2020, there were more 55 million people living around the world with dementia, with an estimated 10 million new cases each year. Experts estimate that someone develops the condition every 3 seconds.
For decades, researchers have suspected a connection between mental health conditions earlier in life and dementia later in life, although the results of such research have been mixed. inconsistent.
Now, researchers from the University of Michigan in Ann Arbor, Duke University in Durham, NC, and the University of Auckland in New Zealand have published a long-term study of 1.7 million New Zealand people ages 21 to 60. .
The integrative nature of the country’s national health system allowed the study authors to follow people for 30 years, from 1988 to 2018, linking hospital records and population databases.
The study finds that mental health The conditions are strongly associated with dementia later in life.
The study appears in JAMA Psychiatry.
While the study reveals a strong statistical association between mental health conditions and dementia, a longitudinal study like this cannot prove that prior mental health problems cause dementia.
The lead author of the study is Leah Richmond-Rakerd, MD, assistant professor in the Department of Psychology at the University of Michigan. she suggested to Today’s medical news Some reasons why such a strong association might exist:
“There could be shared risk factors for both mental illness [health conditions] and dementia, such as shared genetics. It could also be that people experience a brain vulnerability that manifests as mental health problems earlier in life and manifests as dementia later in life.”
Dr. Archana Singh-Manouxwho was not involved in this study, said MNT who agrees that this explanation is possible.
However, “it is more likely that [having a mental health condition] early in life sets you on pathways that lead to adverse health outcomes. This could include harmful behaviors, poor health care, treatment noncompliance, poverty, medication side effects, etc.”
Dr. Singh-Manoux is a principal investigator in the epidemiology of aging and neurodegenerative diseases at the University of Paris in France.
“However, it is important to keep in mind,” said Dr. Richmond-Rakerd, “that even if mental health conditions are not a causal risk factor for dementia, the presence of a mental health problem is still a risk factor. important indicator of risk.
“the mental [health conditions] considered in the study,” explained Dr. Singh-Manoux, “were: substance use, psychopath, mood, neurotic (ie, anxiety), physiological disorders, personality, developmental, behavioral and unspecified disorders”.
As lead author of a previous study exploring a link between depression and dementia, Dr. Singh-Manoux noted:
“It is important to separate these findings from studies examining the association between depressive symptoms and dementia, particularly studies based on older adults. This is because depressive symptoms are common in the preclinical phase of dementia, and it is likely that any association is due to ‘reverse causality’.
In other words, dementia in older adults may be an early sign of dementia, rather than evidence that depressive symptoms are a risk factor for dementia.
The study found that mental health conditions were associated with later Alzheimer’s and non-Alzheimer’s dementias, as well as other early and late onset dementias.
Of the total group studied, the researchers identified that 3.8% (64,857) of people had a mental health condition, while 2% (34,029) had a diagnosis of dementia.
Just over 6% of people with mental health problems developed dementia during the observation period. Among those without mental health problems, only 1.8% developed dementia.
The association persisted across all genders and age groups.
The researchers also determined that socioeconomic deprivation or previous chronic physical illnesses were not significant factors.
“We were surprised to find that mental health conditions were a much stronger predictor of dementia than chronic physical illnesses,” said Dr. Richmond-Rakerd.
“This reinforces the need,” said Dr. Richmond-Rakerd, “to think about dementia prevention earlier in the life course because mental health conditions tend to peak in young adulthood, whereas chronic physical illnesses usually do not arise until later in life. Supporting the mental health of young people could be a window of opportunity to help reduce the burden of dementia in older adults.”
MNT asked Dr. Richmond-Rakerd what kind of research she would like to see that could establish or disprove a causal connection between mental health conditions and dementia. She answered:
“An informative approach would be to identify successful randomized clinical trials of psychiatric interventions and follow up with the participants who received the intervention to see if they are doing better in the future in terms of their cognitive health and are protected from dementia. This would provide evidence that mental health conditions are a causal risk factor.”
However, said Dr. Singh-Manoux, “Establishing causality when it comes to dementia is complicated by the long period over which dementia develops, perhaps 15 to 20 years. [Randomized controlled trials]the gold standard method of establishing causality, they are clearly not helpful.”
This left Dr. Singh-Manoux with more faith in longitudinal studies like the one by Dr. Richmond-Rakerd:
“Therefore, well-conducted longitudinal studies, with long follow-up, are crucial.” He added: “Another approach is Mendelian randomization, where genes are used as instruments to test for causality in the association between an exposure and an outcome.”
