Some difficult feelings that people often chalk up to normal midlife struggles — loss of confidence, trouble concentrating — may in fact be signs of depression. Research has shown that depression can increase dementia risk later in life.
“We found that not everyone with depression in midlife has a higher risk of developing later dementia — the increased risk appears to be driven by a small number of specific symptoms,” says the lead author, Philipp Frank, PhD, a research fellow in psychiatry at University College London.
Depression Raised Dementia Risk by 27 Percent
Almost 6,000 middle-aged British government workers participated in the study. All received a questionnaire listing a total of 30 specific depression symptoms and indicated whether and how often they had experienced each symptom during the previous two weeks.
Over the next 23 years, the researchers tracked participants using national health registries, with dementia diagnoses recorded up to 2023. The long follow-up period allowed investigators to look for mood changes that often show up long before typical dementia-related symptoms like memory loss start happening.
About 10 percent of people developed dementia over the two decades plus of follow-up.
After adjusting for factors that could influence dementia risk, such as age and sex, the scientists found that people classified as depressed (those reporting five or more symptoms) had a 27 percent higher risk of subsequent dementia.
“These findings are another demonstration that midlife depression or depressive symptoms are associated with an increased risk of developing late-life dementia,” says Victor Henderson, MD, the director of the Stanford Alzheimer’s Research Center and a professor of epidemiology and population health at Stanford Medicine in Palo Alto, California, who wasn’t involved in this study.
Specific Depression Symptoms Linked to Later Dementia
The UK study also identified an association between six specific depression symptoms and a later dementia diagnosis, on the basis of these participant responses to the questionnaire:
- Losing confidence in myself
- Not able to face up to problems
- Not feeling warmth and affection for others
- Nervous and strung-up all the time
- Not satisfied with the way tasks are carried out
- Difficulties concentrating
In particular, loss of self-confidence and difficulty coping with problems were each associated with a roughly 50 percent increased risk of dementia.
Sleep Issues and Low Mood Weren’t Linked to Later Dementia Risk
Somewhat surprising were the symptoms that did not appear to impact future cognitive decline.
“Importantly, some of the most commonly seen symptoms in both our study and routine clinical practice, such as low mood or sleep disturbances, were not associated with increased dementia risk,” says Dr. Frank.
The Study Has Some Limitations
While Dr. Henderson agrees that the overall findings on the link between depressive symptoms and dementia make sense, he found the data that zeroed in on the associated risk of specific symptoms to be weaker.
“These are depressive symptoms, but not necessarily part of a depression diagnosis, and it’s looking at a very limited time period — two weeks before completing the assessment,” he says.
Because the participants were mostly white men, it isn’t clear if these findings would apply to women or people of other races or ethnicities. Although sex was a factor in the analysis, the researchers did not report separate results by gender. Larger and more diverse studies will be needed to understand whether these patterns play out differently in people other than white men, the authors noted.
Chronic Depression May Impact the Brain Through Increased Inflammation and Stress Hormones
Scientists can’t entirely explain the link between depression and dementia. Previous research suggests depression may be a risk factor for dementia, a prodromal symptom (an early sign of cognitive decline), or both.
Chronic depression has been associated with biological changes that may affect brain health over time, including increased inflammation, changes in stress hormones, vascular damage, and reduced brain plasticity (meaning impairment to the brain’s ability to learn and adapt).
What Can People Do to Prevent Dementia?
For anyone who struggles with the symptoms identified in the study, psychological therapies and antidepressants may offer some brain protection, but more research is needed to understand how such treatments influence long-term dementia risk, says Frank.
The findings do affirm that people who struggle with depression or symptoms of depression should seek medical care, says Henderson, but the takeaway should not be that some symptoms of depression “matter” more than others when it comes to dementia risk.
“Many of these symptoms are interconnected — if you improve one, it’s likely that others will get better as well,” he says.
Improved depression symptoms could also help a person make certain lifestyle changes that boost brain health. For instance, increased self-confidence could help a person become more social and engage in more situations that stimulate thinking, thereby maintaining their cognitive reserve, the study authors wrote.
Cognitive reserve is the brain’s ability to cope with damage or disease by adapting and finding new ways to get things done — basically brain resilience. Experts believe people build their cognitive reserves over a lifetime through learning, curiosity, and mentally engaging activities.