Depression is highly prevalent in most dementias and it is associated with significant functional and cognitive decline, chronicity and high rates of medical comorbidity and mortality. The nature of the link between depression and dementia is still unclear. Given the projected growth of the older segment of the population, a better understanding of the link between them is important, especially for possible treatment and prevention.

To review the complex relationship between late life depression and dementia, to discuss the underlying mechanisms and implications for the diagnosis and treatment of both conditions.

Review of the relevant literature published in the Medline database

There is evidence to support the notion of depression as a risk factor as well as a prodromal symptom of dementia. It also shows that both conditions show similar neurobiological changes, either indicating shared risk factors or a common pattern of neuronal damage. The likely underlying biological mechanisms include vascular disease, hippocampal atrophy, increased deposition of β-amyloid plaques and inflammatory changes. These processes are not mutually exclusive and more likely synergistic, which explains the substantial variability of findings from the literature.

This work highlights that strategies to promote prevention, early diagnosis and adequate treatment of depression may have a major impact in reducing the risk or delaying dementia in older adults. Additionally, more conclusive research on the underlying neurobiological pathways, may pave the way for more effective treatment of both depression and dementia.