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Nodding off during the day could be an early sign of Alzheimer’s disease, research suggests.

A study of nearly 300 retirees found those who reported being sleepy during the day had higher accumulations of a damaging protein, known as amyloid, in their brains.

The US scientists, from the Mayo Clinic in Minnesota, said the brain naturally clears the protein – which forms sticky plaques – while the body sleeps.

The researchers suggest that those who suffer broken sleep at night, and therefore struggle to remain awake during the day, are more likely to have dangerous build-ups of this protein. This means ‘excessive’ tiredness in the elderly should be considered a red flag for the disease, they said.

In the study, published in the JAMA Neurology journal, scientists tracked 283 participants aged over 70 between 2009 and 2017 and assessed their levels of daytime sleepiness as well as conducting brain scans on each.

The fifth of participants who reported daytime sleepiness had more buildups of amyloid plaques, particularly in areas of the brain linked to learning and memory, it was found.