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The less older adults sleep, the faster their brain shrinks and declines, researchers have warned.

Researchers say the findings could have important implications for the rise of dementia among the elderly.

The team studied 66 older Chinese adults, who underwent MRI scansas well as completing sleep surveys.

The less older adults sleep, the faster their brain shrinks and declines, researchers have warned - and it believed older adults are particularly at risk.

Researchers at Duke-NUS Graduate Medical School Singapore (Duke-NUS) said those who slept fewer hours showed evidence of faster ventricle enlargement and decline in cognitive performance.

These findings, relevant in the context of Singapore's rapidly ageing society, pave the way for future work on sleep loss and its contribution to cognitive decline, including dementia.

Past research has examined the impact of sleep duration on cognitive functions in older adults.

Though faster brain ventricle enlargement is a marker for cognitive decline and the development of neurodegenerative diseases such as Alzheimer's, the effects of sleep on this marker have never been measured.

The Duke-NUS study examined the data of 66 older Chinese adults, from the Singapore-Longitudinal Aging Brain Study.

Participants underwent structural MRI brain scans measuring brain volume and neuropsychological assessments testing cognitive function every two years.

Additionally, their sleep duration was recorded through a questionnaire.

Those who slept fewer hours showed evidence of faster ventricle enlargement and decline in cognitive performance.

'Our findings relate short sleep to a marker of brain aging,' said Dr June Lo, the lead author and a Duke-NUS Research Fellow.

'Work done elsewhere suggests that seven hours a day for adults seems to be the sweet spot for optimal performance on computer based cognitive tests.

In coming years we hope to determine what's good for cardio-metabolic and long term brain health too,' added Professor Michael Chee, senior author and Director of the Centre for Cognitive Neuroscience at Duke-NUS.

Earlier this week researchers warned sleeping too much in middle age can be just  as bad for you as not having enough.

A study of almost 9,000 people found those aged  50 to 64 who slept for less than six hours a night or more than eight had worse memories and decision-making abilities.

But brain power was only reduced for older adults of 65 to 89 if they slept too long.

The sleep findings pave the way for future work on sleep loss and its contribution to cognitive decline, including dementia, the researchers say

The dangers of having too  little sleep are well established, but the latest study, carried out by experts at the University of Warwick, indicates that an excess can create similar problems.

Researcher Dr Michelle Miller said the results also suggest that the amount of sleep we need – and its affect on the body and brain – changes with age.

Co-author Professor Francesco Cappuccio claimed getting just the right amount of sleep among the elderly could even prevent the age-related mental decline that can result in dementia.

He added: 'Sleep is important for good health and mental wellbeing.

'Optimising sleep at an older age may help to delay the decline in brain function seen with age, or may slow or prevent the rapid decline that leads to dementia.'

Dr Miller said: 'Six to eight hours of sleep per night is particularly important for optimum brain function in younger adults.

'These results are consistent with our previous research, which showed six to eight hours per night was optimal for physical health, including lowest risk of developing obesity, hypertension, diabetes, heart disease and stroke.'