Late-life depression is usually considered a chronic course, accompanied by cognitive impairment. Depression is considered to be one of the risk factors of dementia or a prodrome of dementia. Research
[23] suggests that late-life depression may increase dementia risk by twofold. A recent meta-analysis
[24] showed that depression in later years is associated with dementia in all forms. Further analysis discovered that the risk (2.52, 95% CI 1.77–3.59,
p < 0.001) of vascular dementia is higher than Alzheimer`s disease (1.65, 95% CI 1.42–1.92,
p < 0.001).
The two seem to overlap in some neurobiological findings. The theory of the HPA axis is currently the most consistent in depression research. Elevated cortisol level can also cause hippocampus neuronal loss and volume reduction
[25][26]. Hypercortisolemia can also be seen in the CSF of patients with Alzheimer’s disease (AD)
[27]. Vascular depression refers to the appearance or aggravation of depression after the occurrence of cerebrovascular events. In addition to WMHs seen on neuroimaging, there are lesions on small blood vessels (maybe subcortical infarcts, microbleeding, etc.). In addition, in cases of depression, decreased blood flow in the brain may also lead to hyperactivity of the hippocampus and amygdala
[28]. Inflammation can be seen in people with AD and depression, due to an increase in activated microglia in the CNS
[29][30]. Microglial cells that are continuously activated have a reduced ability to remove neurotoxic agents, leading to a reduction in neuronal loss and neurogenesis
[28]. An increase in peripheral proinflammatory markers is also associated with the severity of depressive symptoms and cognitive impairment
[31]. Neurotrophic factors include BDNF, the main function of which is to regulate synaptic plasticity, which plays an important role in learning and memory. It has been found in patients with depression that the use of antidepressants can increase the concentration of BDNF in the blood
[24][32]. In patients with AD, the severity of cognitive impairment is related to BDNF and amyloid beta (Aβ1–42) plasma levels in serum
[33][34]. Although the current research has found some common neurobiological changes in depression and AD, there are overlaps in symptoms. However, according to the current research, there is insufficient evidence that antidepressants can improve the cognition of depression in the elderly and the depression symptoms of AD
[35][36][37][38].