A longitudinal study of older adults in China found that those with depression were almost five times more likely to develop Alzheimer’s disease than those without depression. The risk of developing vascular dementia was 1.9 times higher. The paper is psychiatric research.
Dementia is a general term that refers to a group of neurocognitive disorders characterized by declines in memory, thinking, and daily functioning. Although the risk of developing dementia clearly increases with age, it is not a normal part of aging. This is caused by underlying brain pathology, such as neurodegeneration, vascular damage, and abnormal protein accumulation.
The most common dementia is Alzheimer’s disease, followed by vascular dementia, Lewy body dementia, and frontotemporal dementia. Symptoms typically include memory loss, impaired reasoning, language impairment, and changes in personality and behavior. Early stages are associated with mild forgetfulness, while later stages are characterized by severe disorientation and loss of independence.
Study author Elaine He Xu and 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. The researchers noted that while previous studies have investigated the association between depression and dementia, many have not distinguished between specific subtypes of the disease or examined the timeline of this association longitudinally.
The study authors analyzed data from electronic medical records in Yichang, a city located in central mainland China. The Yichang Electronic Medical Records System integrates general demographic data with inpatient and outpatient records, disease diagnoses, prescriptions, and medical cost data from 160 local medical facilities. The total number of databases covered 921,289 residents from 2015 to 2023.
From this dataset, researchers focused on individuals aged 50 and older who were free of dementia at the start of the study period (January 2016) and had complete medical records available. In total, they analyzed data from 4,341 depressed patients and matched them with 43,214 non-depressed individuals who shared similar key characteristics (such as age and gender).
Of these, approximately 62% were women, and their average age at the start of the study was 64 years. Individuals diagnosed with schizophrenia, schizoaffective disorder, or bipolar disorder were excluded from analyzes to isolate the specific effects of depression.
Results showed that during an average follow-up period of 3.6 years, 1,493 people in the dataset developed dementia. The average age at first diagnosis of dementia was 78 years.
Compared to their non-depressed peers, people with depression had a 2.2 times higher risk of developing any type of dementia. People with depression had an almost five times higher risk of developing Alzheimer’s disease. The risk of developing vascular dementia was almost doubled. Further analysis revealed that this increased risk of Alzheimer’s disease and vascular dementia was particularly present in older adults (60 years and older) diagnosed with depression.
Importantly, researchers found a “U-shaped” temporal relationship between depression and Alzheimer’s disease. The risk of being diagnosed with Alzheimer’s disease increased sharply in two different time periods: within two years and six to eight years after being diagnosed with depression.
Researchers suggest this means that depression works in two ways. Short-term late-life depression may actually be a “prodromal symptom,” an early warning symptom of underlying undiagnosed Alzheimer’s disease. Conversely, long-term depression (lasting 6-8 years) acts as a physical risk factor, with long-standing immune dysregulation and biological stress actively promoting brain degeneration. Interestingly, this U-shaped pattern was unique to Alzheimer’s disease. For vascular dementia, the risk increased only after 6 to 8 years of exposure to long-term depression.
“Our study shows a strong association between depression and incident dementia, with AD (Alzheimer’s disease) showing a stronger correlation than VD (vascular dementia). The unique temporal association suggests that depression may serve as both a risk factor and prodrome for AD, and only as a risk factor for VD,” the study authors concluded.
This study contributes to the scientific understanding of the association between dementia and depression in older adults. However, because this study data was obtained from a single city with a relatively homogeneous population, results may vary in other countries or geographic regions.
Furthermore, the study authors report that the proportion of people diagnosed with Alzheimer’s disease in their dataset was lower than estimates from national surveys in China, leaving the possibility that Alzheimer’s disease was underdiagnosed in the study area. Finally, this dataset lacked information on lifestyle factors such as smoking, diet, and exercise that are known to influence dementia risk.
The paper, “The impact of depression on the risk 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.
