New Delhi: Mood changes after 40 could be more than just mental health issues, they might be early warning signs of serious brain diseases.
A new study by researchers from Japan’s National Institutes for Quantum Science and Technology (QST) suggests that mood disorders such as depression, bipolar disorder, or mania beginning after the age of 40 may actually signal the onset of neurodegenerative diseases like Alzheimer’s.
The study, published in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, found a strong link between late-life mood disorders (LLMDs) and the presence of abnormal tau proteins in the brain, which are a well-established hallmark of several neurodegenerative diseases.
Researchers used advanced brain imaging techniques including positron emission tomography (PET) scans with two types of tracers to detect tau and amyloid beta deposits in the brains of 52 participants with LLMDs and 47 healthy control participants.
They also analysed brain tissue from 208 autopsy cases to investigate the long-term correlation between mood symptoms and neurodegenerative changes.
The results were striking. Approximately 50 percent of participants with LLMDs showed tau accumulation, compared to only 15 percent of healthy individuals.
Moreover, nearly 29 percent of those with LLMDs had detectable levels of amyloid plaques, a key marker of Alzheimer’s disease, whereas just 2 percent of the healthy controls did.
"Because most of the participants with LLMDs in our study had no or mild cognitive decline, these results support the evidence that neurodegenerative diseases, including Alzheimer’s and non-Alzheimer’s tau-related pathologies, can initially manifest as psychiatric symptoms," said Dr Shin Kurose from QST.
The team also noted significant tau deposits in the frontal lobes of the brain, areas vital for emotional regulation and higher-order cognitive functions. This observation adds weight to the idea that mood disturbances could be rooted in early biological changes linked to dementia.
According to the autopsy findings, mood symptoms like depression or mania preceded the onset of cognitive or motor symptoms by an average of 7.3 years. The researchers believe this time window could offer a crucial opportunity for early detection and treatment.
"Timely identification of late-life depression and bipolar disorder would allow for earlier intervention with disease-modifying treatments," the team said.
The growing body of evidence from this study adds urgency to the need for rethinking how mood disorders in older adults are assessed, not just as isolated mental health concerns, but as potential red flags for deeper, underlying neurodegenerative processes.