CANBERRA, March 17 (Xinhua) -- Poor sleep in middle age can have a negative impact on brain health, according to a recent study by researchers from the Australian National University (ANU).

The study, which was published on Thursday, examined the sleep habits of 29,000 people aged between 37 and 73.

It found that getting fewer than six hours of sleep a day or more than nine hours was associated with lower brain volume and cognitive measures, which are crucial for things like reaction time and memory. Daytime dozing was also found linked to impaired brain health.

Tergel Namsrai, leader of the research and a PhD candidate at ANU, said the findings could provide the basis for combating neurodegenerative diseases such as dementia.

"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 in a statement.

"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."

The World Health Organisation (WHO) estimates that more than 55 million people worldwide currently have dementia - a figure that is expected to rise to 150 million by 2050.

A report published by the Australian Institute of Health and Welfare (AIHW) in February revealed dementia has surpassed heart disease as the leading cause of disease burden in older Australians for the first time.

There is currently no cure for dementia, which Namsrai said made it more important to identify risk factors.

"Around 20 to 40 percent of dementia cases are attributable to modifiable, non-genetic factors," she said.

"The most well-known of these include smoking, alcohol misuse and obesity. But sleep is an emerging risk factor."