From the article: The study looked at the sleep habits of over 29,000 people aged between 37 and 73 and could provide the basis for helping to combat major diseases like dementia.

According to lead author and PhD candidate Dr Tergel Namsrai, it’s not just lack of sleep that can impair brain health.

“Getting more than nine hours of sleep a day or less than six hours were both associated with lower brain volume and cognitive measures – crucial for things like reaction time and memory,” Dr Namsrai said.

“Daytime dozing was also associated with some of these indicators of impaired brain health.”

Dr Namsrai said there needs to be greater focus on the links between sleep and brain health, as well as more research into ways to improve sleep.

“The mechanisms underlying the link between sleep and brain health are not well understood – there’s a lot of work to be done,” she said.

“But our study shows it could be an important target if we want to improve brain health into old age and delay the onset of dementia."

Dementia is among the world’s leading causes of death worldwide and is expected to impact 150 million people by 2050.