Depression may be a stronger warning sign for dementia than insomnia

A recent study published in the Journal of Affective Disorders suggests that experiencing both depression and insomnia symptoms were linked to higher dementia risks among older adults. However, depressive symptoms alone may be the stronger warning sign. The findings provide evidence that screening for mood and sleep issues as people age may help identify those who might need closer monitoring.

Alzheimer’s disease and related dementias are a growing public health concern as populations age globally. Estimates suggest that tens of millions of people live with dementia worldwide, and this number is projected to rise significantly in the coming decades. Finding ways to recognize who is at risk before memory and thinking problems become severe is a major priority for scientists.

Two common health concerns in older adults are depressive symptoms and insomnia symptoms. Depression can involve persistent feelings of sadness, hopelessness, or a lack of interest in daily activities. Insomnia symptoms can include difficulty falling asleep or staying asleep on a regular basis.

In a joint statement, study authors Sofia Liu and Junxin Li, researchers at the Johns Hopkins University School of Nursing, explained their reasons for starting the project. “We were motivated by the fact that both depressive and insomnia symptoms are common in older adults, and in everyday life these symptoms don’t always happen in isolation – many people experience them together,” they said. Both symptoms share biological links in the body and brain, such as altering how the body handles stress and inflammation.

Previous research mostly looked at depressive and insomnia symptoms separately. “On their own, each has already been linked to a higher risk of dementia in previous research,” the authors said. “We wanted to better understand whether older adults who have both symptoms may be at particularly high risk, compared with those who have just one symptom or neither. Our goal was to help identify groups of older adults who may be more vulnerable, so that risk can potentially be recognized earlier.”

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To investigate this, the researchers analyzed data from the National Health and Aging Trends Study. This is a large, nationally representative survey of Medicare beneficiaries aged 65 and older in the United States. The final sample included 6,226 older adults who lived in the community and did not have dementia when they started the study. The scientists followed these participants for up to 12 years, collecting data across 13 different survey rounds between 2011 and 2023.

At each survey round, participants answered questions about their mood and sleep. To measure depressive symptoms, participants rated how often in the past month they felt down, depressed, or hopeless, and how often they had little interest in doing things. To measure insomnia symptoms, participants reported how frequently they had trouble falling asleep or returning to sleep after waking up in the night. If someone experienced these issues on most nights or every night, they were considered to have insomnia symptoms.

Based on these answers, the scientists sorted participants into four groups at every check-in. The categories were people with neither symptom, those with only depression, those with only insomnia, and those experiencing both insomnia and depressive symptoms together. By updating these groupings at each round, the researchers could track how symptoms evolved over time. The authors determined if a participant developed dementia using several sources of information, including doctor diagnoses, brief cognitive tests, and reports from proxy informants who were familiar with the participant’s daily functioning.

The overall analysis provided evidence that older adults with co-occurring depressive and insomnia symptoms had a higher risk of developing dementia compared to those with neither symptom or those with only insomnia symptoms. “The effects were meaningful at the population level, but they should not be interpreted as predicting what will happen to any one individual,” the authors noted. “In the overall model, older adults with co-occurring depressive and insomnia symptoms had about 37% higher dementia hazard than those with neither symptom and about 25% higher hazard than those with insomnia symptoms alone.” In statistical terms, a higher hazard means a higher rate of developing dementia during the study period.

However, the risk of dementia for people with both symptoms did not differ significantly from those who only experienced depressive symptoms. “At the same time, the co-occurring group did not have significantly higher dementia hazard than the depression-only group, which suggests that depressive symptoms may be especially important for dementia-risk stratification in later life,” Liu and Li explained. “From a practical standpoint, both depressive and insomnia symptoms are worth clinical attention, but depressive symptoms appeared to be the more consistent signal in our analyses.”

This specific outcome was not what the scientific team anticipated. “What surprised us was that the co-occurring depression-insomnia group was not consistently at higher risk than the depression-only group,” the researchers said. “We initially expected that having both depressive and insomnia symptoms would show the highest dementia risk across analyses.”

“Instead, depression-only often looked similar to co-occurring symptoms, and in some subgroup analyses, particularly among older participants, the depression-only group showed even higher dementia hazard than the co-occurring group. This finding suggests that depressive symptoms alone should not be minimized, even when insomnia symptoms are absent.”

The researchers found that age changed how these symptoms related to dementia risk, while biological sex did not. For participants under the age of 75, having both symptoms was linked to a higher risk of dementia than having just insomnia or neither symptom. For participants aged 75 and older, individuals with only depression actually showed 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 takeaway is that depressive symptoms in later life should be taken seriously, whether they occur alone or together with insomnia symptoms,” they stated.

“In our study, older adults with both depressive and insomnia symptoms had higher dementia risk than those with neither symptom or insomnia symptoms alone. However, their risk was not clearly higher than those with depressive symptoms alone, and in some age-stratified analyses, the depression-only group showed equal or even higher risk than the co-occurring group.”

The researchers hope these insights guide better health screenings for aging adults. “So while we do want to highlight the importance of looking at mood and sleep together, we also do not want people to overlook depressive symptoms when they occur on their own,” Liu and Li added.

Readers should be cautious not to interpret these findings as proof that depression and insomnia directly cause dementia. In many cases, mood changes and sleep disturbances may reflect early changes related to brain disease that has already started. “A key caveat is that this was an observational study, so the findings should not be interpreted as proof that depressive or insomnia symptoms cause dementia,” the authors explained. Because observational studies only track people over time without assigning treatments, they show associations rather than direct causes.

“These symptoms may contribute to dementia risk, but they may also reflect early changes in brain health, physical health, stress, daily functioning, or other factors that are already unfolding,” they said. They also stressed that risk factors are not guarantees of future health problems. “Another important point is that having depressive or insomnia symptoms does not mean a person will develop dementia; our findings are most useful for understanding broader population-level patterns rather than predicting an individual’s future,” the researchers added.

The researchers also cautioned against overinterpreting the sleep-related findings due to potential measurement limitations. “Our insomnia measure was based on two self-reported symptoms – difficulty falling asleep and difficulty returning to sleep after waking – and did not capture the full multidimensional nature of sleep health, such as sleep duration, sleep regularity, daytime sleepiness, circadian rhythm, sleep apnea, or objective sleep quality,” Liu and Li noted.

“Because of that, we cannot conclude that insomnia is unimportant for cognitive health. Rather, our findings suggest that, with the insomnia measures available in this study, depressive symptoms appeared to be the more consistent marker of dementia risk.”

Moving forward, scientists aim to use more detailed measures of sleep and mood, including objective sleep measures when available. “An immediate next step is to test whether these findings hold when sleep and mood are measured more comprehensively,” the authors said. “Our current study captured depressive symptoms and two insomnia symptoms repeatedly over time, but future work should include broader dimensions of sleep health, such as sleep duration, sleep regularity, daytime functioning, circadian patterns, and objective sleep measures when available.”

“We are also interested in better understanding how mood and sleep symptoms evolve over time and which longer-term symptom patterns are most informative for cognitive health,” Liu and Li said. “Longer term, this work can help inform interventions that address mood and sleep together to support overall health and cognitive health in older adults.”

The study, “Depressive and insomnia symptoms and incident dementia risk: A 12-year study in U.S. older adults,” was authored by Sofia Liu, Zixuan He, Claire Wang, Xiaoyue Liu, Nada Lukkahatai, and Junxin Li.