New research has found that depression diagnosed in midlife or later may not only increase a person’s risk of developing dementia, but could also be an early indicator of the disease itself.

The study, published in eClinicalMedicine, was led by researchers from the University of Adelaide in collaboration with the University of Nottingham and Curtin University. It is one of the most comprehensive investigations to date, combining an umbrella review of eight studies and a meta-analysis of 18 others.

“Our study shows that depression is linked to an increased risk of dementia in both midlife and late life,” said lead author Jacob Brain, the first recipient of a joint PhD scholarship between the University of Nottingham and the University of Adelaide.

The findings provide clearer evidence that depression, particularly in later years, may be more than just a mental health condition—it could be part of the early stages of cognitive decline.

“Depression in late life may represent an early manifestation of dementia,” Brain said. “It may also reflect underlying neurobiological changes that precede the cognitive symptoms.”

Dementia affects more than 57 million people globally, and identifying early risk factors is critical for prevention. This study adds weight to a growing body of evidence suggesting that treating depression effectively could also play a role in protecting long-term brain health.

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“Depression itself may accelerate cognitive decline through mechanisms linked to chronic inflammation and vascular dysregulation, which further weaken neural resilience,” Brain explained. “It is a complex relationship and likely reflects multiple interacting factors.”

Importantly, the study urges health systems to take a broader view of mental health, especially in ageing populations.

“This highlights the importance of recognising and treating depression across the life course, not just for mental health, but also as part of a broader strategy to protect brain health,” said Brain. “Public health efforts need to place greater emphasis on preventative brain health, including scaling up access to effective mental health care.”

By pinpointing the timing and nature of the relationship between depression and dementia, the research team hopes to inform better diagnostic, treatment and prevention strategies in the future.