Depressed elderly adults are almost 5 times more likely to develop Alzheimer’s

A longitudinal study of elderly adults in China found that depressed individuals are at an almost 5 times higher risk of developing Alzheimer’s disease compared to their non-depressed peers. Their risk of developing vascular dementia was 1.9 times higher. The paper was published in Psychiatry Research.

Dementia is a general term used to describe a group of neurocognitive disorders characterized by a decline in memory, thinking, and daily functioning. While the risk of developing dementia clearly increases with age, it is not a normal part of aging. It is caused by underlying brain pathology, such as neurodegeneration, vascular damage, or abnormal protein accumulation.

The most common form of dementia is Alzheimer’s disease, followed by vascular dementia, Lewy body dementia, and frontotemporal dementia. Symptoms typically include memory loss, impaired reasoning, language difficulties, and changes in personality or behavior. Early stages involve mild forgetfulness, while later stages are characterized by severe disorientation and a loss of independence.

Study author Elaine He Xu and her colleagues investigated the relationship between depression and two specific types of dementia—Alzheimer’s disease and vascular dementia—in a large group of Chinese adults. They noted that while previous studies had explored the association between depression and dementia, many did not differentiate between the specific subtypes of the disease, nor did they explore the timeline of this association longitudinally.

The study authors analyzed data from electronic health records in Yichang, a city located in central mainland China. The Yichang electronic health record system integrates general demographic data with inpatient and outpatient records, disease diagnoses, prescriptions, and health cost data from 160 local healthcare facilities. The total database covered 921,289 residents between 2015 and 2023.

From this dataset, the researchers focused on individuals aged 50 years and older who were dementia-free at the start of the study period (January 2016) and had complete medical records available. In total, they analyzed data from 4,341 depressed individuals and matched them with 43,214 non-depressed individuals who shared similar key characteristics (such as age and sex).

Approximately 62% of these individuals were women, and their average age at the start of the study was 64 years. Individuals diagnosed with schizophrenia, schizoaffective disorders, or bipolar disorder were excluded from the analysis to isolate the specific effects of depression.

Results showed that, during the average 3.6-year follow-up period, 1,493 individuals in the dataset developed dementia. The average age at the first diagnosis of dementia was 78 years.

Compared to their non-depressed peers, depressed individuals had a 2.2 times higher risk of developing any kind of dementia. The risk of developing Alzheimer’s disease was almost 5 times higher for depressed individuals. The risk of developing vascular dementia was almost twice as high. Further analysis revealed that this increased risk for Alzheimer’s and vascular dementia was specifically present among older adults (aged 60 and older) diagnosed with depression.

Crucially, the researchers discovered a “U-shaped” temporal relationship between depression and Alzheimer’s disease. The risk of an Alzheimer’s diagnosis spiked at two distinct timeframes: less than two years after a depression diagnosis, and again six to eight years later.

The researchers suggest this means depression acts in two ways. Short-term, late-life depression may actually be a “prodrome”—an early warning symptom of underlying, undiagnosed Alzheimer’s disease. Conversely, long-term depression (lasting six to eight years) acts as a physical risk factor, where years of immune dysregulation and biological stress actively contribute to brain degeneration. Interestingly, this U-shaped pattern was unique to Alzheimer’s; for vascular dementia, the risk only increased after a long-term depression exposure of six to eight years.

“Our study demonstrates a robust association between depression and incident dementia, with AD [Alzheimer’s disease] showing the stronger correlation than VD [vascular dementia]. The unique temporal association suggests that depression may serve as both a risk factor and a prodromal symptom for AD, and solely as a risk factor for VD,” the study authors concluded.

The study contributes to the scientific understanding of the links between dementia and depression in older adults. However, the study data came from a single city with a relatively homogenous population, meaning findings in other countries and geographical areas may differ.

Additionally, the study authors report that the proportion of people diagnosed with Alzheimer’s disease in their dataset was lower than Chinese national survey estimates, leaving the possibility that the condition was underdiagnosed in the studied area. Finally, the dataset lacked information on lifestyle factors like smoking, diet, and exercise, which are known to influence dementia risk.

The paper “Effect of depression on risks of Alzheimer’s disease and vascular dementia: a real-world longitudinal study” was authored by Elaine He Xu, Yueqing Wang, Weihao Shao, Jiajuan Yang, Xiaoxia Wei, Xunliang Tong, Chi Hu, Enying Gong, Luzhao Feng, Maigeng Zhou, Zuolin Lu, and Ruitai Shao.