A recent study published in the Journal of Affective Disorders indicates that older adults who experience both depressive symptoms and insomnia face a heightened risk of developing dementia. However, depressive symptoms alone may serve as an even stronger warning sign. The findings suggest that screening for mood and sleep issues in later life could help identify individuals who require closer monitoring.
Alzheimer’s disease and related forms of dementia are becoming an escalating public health challenge as populations globally continue to age. It is estimated that tens of millions of people worldwide are currently living with dementia, and this number is projected to rise dramatically in the coming decades. A key priority for researchers is finding methods to identify at-risk individuals before memory and cognitive problems become severe.
Two common health issues among older adults are depressive symptoms and insomnia symptoms. Depression can manifest as persistent feelings of sadness, hopelessness, or a loss of interest in daily activities. Insomnia symptoms may involve difficulty falling asleep or staying asleep on a regular basis.
In a joint statement, study authors Sophia Liu and Junxin Li from the Johns Hopkins University School of Nursing explained the rationale behind launching the project. “We were motivated by the fact that depressive symptoms and insomnia are prevalent among older adults, and in everyday life, these symptoms do not always appear in isolation—many people experience them simultaneously,” they said. Both symptoms have biological links within the body and brain, such as altering how the body manages stress and inflammation.
Previous research has primarily examined depressive symptoms and insomnia symptoms separately. “These symptoms on their own have already been associated with an increased risk of developing dementia in prior studies,” the authors stated. “We wanted to gain a better understanding of whether older adults who have both symptoms are at a particularly high risk compared to those who have only one symptom or none. Our goal was to help identify groups of older adults who may be more vulnerable, so that risk could potentially be detected at an earlier stage.”
To investigate this question, the researchers analyzed data from the National Health and Aging Trends Study. This is a large, nationally representative study of Medicare beneficiaries aged 65 and older in the United States. The final sample included 6,226 older adults living in the community who were free of dementia at the start of the study. The scientists followed these participants for 12 years, collecting data across 13 different study waves between 2011 and 2023.
At each survey wave, participants answered questions about their mood and sleep. To assess depressive symptoms, participants indicated how often over the past month they felt depressed, down, or hopeless, as well as how often they lost interest in activities. For insomnia symptoms, participants reported how often they had trouble falling asleep or getting back to sleep after waking up during the night. If a person experienced these problems nearly every night, they were considered to have insomnia symptoms.
Based on these responses, the scientists divided participants into four groups at each study wave. The categories included individuals with no symptoms, those with only depression, those with only insomnia, and those experiencing both insomnia and depressive symptoms simultaneously. By updating these groups at each wave, the researchers could track how symptoms changed over time. The authors determined whether a participant developed dementia using multiple information sources, including physician diagnoses, brief cognitive tests, and reports from informants familiar with the participant’s daily life.
Overall analysis revealed that older adults with co-occurring depressive and insomnia symptoms had a higher risk of developing dementia compared to those with no symptoms or only insomnia symptoms. “The effects were significant at the population level, but they should not be interpreted as predicting what will happen to any specific individual,” the authors noted. “In the overall model, older adults with co-occurring depressive and insomnia symptoms had roughly a 37% higher risk of developing dementia than those with no symptoms, and about a 25% higher risk than those with only insomnia symptoms.” Statistically, a higher risk indicates a greater likelihood of developing dementia during the study period.
However, the risk of developing dementia for those with both symptoms was not significantly different from the risk for those experiencing only depressive symptoms. “At the same time, the group with co-occurring symptoms did not have a significantly higher risk of dementia than the group with depression alone, suggesting that depressive symptoms may be particularly important for stratifying dementia risk in older age,” explained Liu and Li. “From a practical standpoint, both depressive symptoms and insomnia warrant clinical attention, but depressive symptoms appeared to be a more consistent signal in our analysis.”
This finding came as a surprise to the research team. “We were surprised that the group with combined depressive and insomnia symptoms did not always have a higher risk of developing dementia than the group with depression alone,” the researchers stated. “Initially, we expected that having both depressive symptoms and insomnia would show the highest risk of dementia in all analyses.”
“Instead, symptoms presenting as depression alone often resembled symptoms accompanied by other conditions, and in some subgroup analyses, particularly among older participants, the depression-only group exhibited an even higher risk of developing dementia than the co-occurring group. This finding suggests that depressive symptoms alone should not be underestimated, even in the absence of insomnia symptoms,” the authors explained.
The researchers discovered that age modifies the relationship between these symptoms and dementia risk, while biological sex had no effect. Among participants younger than 75, having both symptoms was associated with a higher risk of developing dementia than having only insomnia or no symptoms. For participants aged 75 and older, individuals suffering from depression alone had a higher risk of dementia than those with both symptoms.
Summarizing the practical implications of these patterns, the authors emphasized the need for monitoring mental health at different life stages. “The key takeaway is that depressive symptoms in older age should be taken seriously, whether they occur in isolation or combined with insomnia symptoms,” they stated. “In our study, older adults with depressive and insomnia symptoms had a higher risk of developing dementia than those with no symptoms or only insomnia symptoms. However, their risk was not clearly higher than that of those with only depressive symptoms, and in some age-specific analyses, the depression-only group showed an equal or even higher risk than the co-occurring group.”
The researchers hope these findings will improve medical screenings for older adults. “Therefore, while we want to emphasize the importance of concurrently analyzing mood and sleep, we also do not want people to ignore depressive symptoms when they occur on their own,” added Liu and Li.
However, these results should be interpreted with caution as evidence that depression and insomnia directly cause dementia. In many cases, mood changes and sleep disturbances may reflect early changes related to already progressing brain disease. “An important caveat is that this was an observational study, so the results should not be interpreted as proof that depressive symptoms or insomnia cause dementia,” the authors explained. Because observational studies only track people over time without assigning treatments, they demonstrate associations rather than direct causes.
“These symptoms may contribute to dementia risk, but they could also reflect early changes in brain health, physical health, stress, daily life, or other factors that are already manifesting,” they stated. They also emphasized that risk factors do not guarantee future health problems. “Another important point is that having depressive symptoms or insomnia does not mean a person will necessarily develop dementia; our findings are most useful for understanding broader patterns at the population level, rather than predicting an individual’s future,” the researchers added.
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