Mood disorders like depression, bipolar disorder, or mania after the age of 40 may not be just mental health conditions but can precede motor or cognitive symptoms in various neurodegenerative diseases, according to a study on Monday.

Growing evidence suggests these late-life mood disorders (LLMDs) could be early warning signs of neurodegenerative diseases like dementia, even when they appear years before memory loss or other cognitive symptoms become apparent, said researchers from the National Institutes for Quantum Science and Technology (QST), Japan.

The study, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association explored the presence of abnormal tau protein -- a hallmark of several neurodegenerative diseases -- in the brains of 52 participants with LLMDs and 47 healthy controls.