Recent research published in Affective Disorders Journal suggest that experiencing both depression and insomnia symptoms is associated with increased risk of dementia in older adults. But depressive symptoms alone may be a stronger red flag. The findings provide evidence that screening for age-related mood and sleep problems may help identify people who need closer monitoring.
As the global population ages, Alzheimer’s disease and related dementia are a growing public health concern. It is estimated that tens of millions of people worldwide are living with dementia, and this number is expected to increase significantly in the coming decades. Finding ways to recognize who is at risk before memory and thinking problems become severe is a top priority for scientists.
Two common health concerns among older adults are depressive symptoms and insomnia symptoms. Depression can be accompanied by persistent feelings of sadness, hopelessness, or disinterest in daily life. Symptoms of insomnia may include difficulty falling asleep or staying asleep on a regular basis.
In a joint statement, study authors Sophia Liu and Junxin Li, researchers at the Johns Hopkins School of Nursing, explained why they started the project. “We were motivated by the fact that symptoms of depression and insomnia are both common in older adults, and that these symptoms do not necessarily occur in isolation in everyday life, but are experienced by many people together,” they said. Both conditions share biological connections between the body and brain, including changes in how the body deals with stress and inflammation.
Previous studies have mainly examined symptoms of depression and insomnia separately. “Each alone has already been associated with an increased risk of dementia in previous studies,” the authors said. “We wanted to better understand whether older adults with both conditions are particularly at risk compared to those with only one or the other. Our goal was to help identify groups of older adults who may be more vulnerable and potentially recognize risk earlier.”
To investigate this, researchers analyzed data from the National Health and Aging Trends Study. This is a large, nationally representative survey of U.S. Medicare beneficiaries age 65 and older. The final sample included 6,226 community-dwelling older adults who did not have dementia at the start of the study. The scientists followed these participants for up to 12 years, collecting data over 13 different research rounds from 2011 to 2023.
In each survey round, participants answered questions about their mood and sleep. To measure symptoms of depression, participants rated how often in the past month they felt depressed, depressed, or hopeless, and how often they felt uninterested in things. To measure insomnia symptoms, participants reported how often they fell asleep or were unable to go back to sleep after waking up during the night. People who experience these problems most nights or every night are likely to have symptoms of insomnia.
Based on these responses, scientists divided participants into four groups at each check-in. The categories were those who had neither symptom, those who had only depression, those who had only insomnia, and those who experienced symptoms of both insomnia and depression at the same time. By updating these groupings from round to round, the researchers were able to track how symptoms progressed over time. The authors used several sources of information to determine whether participants had dementia, including doctors’ diagnoses, simple cognitive tests, and reports from proxy informants familiar with the participants’ daily lives.
The overall analysis provided evidence that older adults with co-occurring symptoms of depression and insomnia are at higher risk of developing dementia than those with no symptoms or only symptoms of insomnia. “While this effect was meaningful at the population level, it should not be interpreted as predicting what will happen to any particular individual,” the authors noted. “In the overall model, older adults with co-occurring symptoms of depression and insomnia had about a 37% higher risk of dementia than older adults with neither condition, and about 25% higher risk than older adults with only symptoms of insomnia.” Statistically, a higher risk means a higher rate of developing dementia during the study period.
However, the risk of dementia for people with both conditions was not significantly different from those experiencing only symptoms of depression. “At the same time, the comorbidity group did not have a significantly higher risk of dementia than the depression-only group, suggesting that symptoms of depression may be particularly important for stratifying dementia risk in later life,” Liu and Li explained. “From a practical perspective, both depression and insomnia symptoms are worthy of clinical attention, but depression symptoms appeared to be a more consistent signal in our analysis.”
This specific result was not what the scientific team expected. “What surprised us was that the group with comorbid depression and insomnia was not consistently at higher risk than the depression-only group,” the researchers said. “We initially expected that people with symptoms of both depression and insomnia would show the highest risk of dementia across all analyses.”
“Instead, depression alone is often similar to co-occurring symptoms, and some subgroup analyzes showed that the depression-only group was at even higher risk of dementia than the co-occurring group, especially in older participants. This finding suggests that depression symptoms alone should not be discounted, even in the absence of insomnia symptoms.”
The researchers found that the relationship between these symptoms and dementia risk varied by age, but not by biological sex. For participants younger than 75 years, having both symptoms was associated with a higher risk of dementia than insomnia alone or neither symptom. For participants aged 75 and older, those with only depression were actually shown to have a higher risk of dementia than those with both symptoms.
Summarizing the practical implications of these patterns, the authors emphasized the need to monitor mental health across different life stages. “The main lesson is that depressive symptoms later in life should be taken seriously, whether they occur alone or together with symptoms of insomnia,” the researchers said.
“Our study found that older adults with symptoms of both depression and insomnia had a higher risk of dementia than those with neither symptoms nor insomnia. However, the risk was not clearly higher than older adults with symptoms of depression alone, and in some age-stratified analyses, the depression-only group had a similar or higher risk than the comorbidity group.”
The researchers hope these insights will help improve health screenings for older adults. “So we want to emphasize the importance of monitoring mood and sleeping together, but at the same time we don’t want people to miss out on symptoms of depression if they develop alone,” Ms Liu and Ms Li added.
Readers should be careful not to interpret these findings as evidence that depression or insomnia are direct causes of dementia. Mood changes and sleep disturbances can often reflect early changes related to brain disease that has already begun. “An important caveat is that this is an observational study, so the results of this study should not be interpreted as evidence that symptoms of depression or insomnia cause dementia,” the authors explained. Observational studies simply follow people over time without assigning a treatment, so they show associations rather than direct causes.
“While these symptoms may contribute to dementia risk, they may also reflect early changes in brain health, physical health, stress, daily functioning, or other factors that are already evident,” the researchers said. They also emphasized that risk factors do not guarantee future health problems. “Another important point is that having symptoms of depression or insomnia does not mean that a person will develop dementia. Our findings are most useful for understanding broader population-level patterns, rather than predicting the future of individuals,” the researchers added.
The researchers also cautioned against overinterpreting sleep-related findings because of potential measurement limitations. “Our measure of insomnia was based on two self-reported symptoms: difficulty falling asleep and difficulty returning to sleep after awakening, and did not fully capture the multidimensional nature of sleep health, including sleep duration, sleep regularity, daytime sleepiness, circadian rhythm, sleep apnea, and objective sleep quality,” Liu and Li noted.
“As such, we cannot conclude that insomnia is not important for cognitive health. Rather, our findings suggest that symptoms of depression appear to be a more consistent marker of dementia risk, given the insomnia measures available in this study.”
Going forward, scientists aim to use more detailed measures of sleep and mood, including objective sleep measurements when available. “The immediate next step is to test whether these results hold when we measure sleep and mood more comprehensively,” the authors said. “While our current study captured symptoms of depression and two insomnia symptoms repeatedly over time, future studies should include broader aspects of sleep health, such as sleep duration, sleep regularity, daytime activity, circadian patterns, and objective sleep measurements when available.”
“We are also interested in better understanding how mood and sleep symptoms change over time, and what long-term symptom patterns are most beneficial for cognitive health,” Liu and Li said. “In the long term, this study will help inform interventions that simultaneously address mood and sleep and support overall health and cognitive health in older adults.”
The study, “Depression and Insomnia Symptoms and Risk of Dementia Development: A 12-Year Study of Older Americans,” was authored by Sofia Liu, Zixuan He, Claire Wang, Xiaoyue Liu, Nada Lukkahatai, and Junxin Li.
