Mental disorders may increase risk for subsequent dementia

Preventing mental disorders in young people might reduce or delay the burden of dementia in older people, according to a new study.

Investing in good mental health care for young people—including evidence-based interventions for mental health problems—could help reduce the burden of neurodegenerative disease, say researchers from the University of Michigan, Duke University and the University of Auckland.

Their study of 1.7 million New Zealanders—aged 21 to 60 years at baseline—followed across three decades (1988 to 2018) tested whether individuals with mental disorders are at increased risk for subsequent dementia.

Much research and treatment in geriatrics focuses on physical diseases and ignores mental health, says Leah Richmond-Rakerd, assistant professor in U-M's Department of Psychology and the study's lead author.

Richmond-Rakerd and colleagues chose New Zealand for its capacity to link medical records and other administrative databases at the population level—something not possible in the United States.

The long-term, follow-up use of hospital records, and the ability to establish that mental disorders preceded dementia set this study apart from others.

Among the study's findings:

• Mental disorders were more strongly associated with dementia than chronic physical diseases—an outcome the researchers did not expect.
• The association between mental disorders and dementia was not explained by preexisting chronic physical illness or socioeconomic deprivation.
• The connection between mental health problems and dementia was seen for both men and women, for both early-onset and later-onset dementias, for different types of mental health conditions and for both Alzheimer's and non-Alzheimer's dementias.

Richmond-Rakerd says mental disorders are salient early-warning signs for subsequent dementia. People with mental disorders could be encouraged to engage in health behaviors to reduce dementia risk—for instance, to increase their physical activity, which so far is one promising way to potentially help prevent dementia, the researchers say.

The mechanism for the association is not clear, but could involve several factors, says co-author Avshalom Caspi, professor of psychology and neuroscience at Duke.

For instance, a lifelong brain vulnerability may manifest itself as mental health problems earlier in life and dementia later in life. Or medication for mental disorders (such as antipsychotics) might increase the risk for dementia, he says.

The researchers caution that most people with mental-health problems will not develop dementia.

"Mental health problems are not a 'life sentence' that always results in dementia," Richmond-Rakerd said.

The study, which appears in JAMA Psychiatry, was also co-authored by Stephanie D'Souza and Barry Milne of the University of Auckland, and Terrie Moffitt of Duke University.