Shortness of sleep speeds up the aging of the brain in older people, say researchers from Duke-NUS Graduate Medical School Singapore.
The research on healthy adults aged 55 years and older, published in the journal Sleep, used magnetic resonance imaging (MRI) and neuropsychological assessment to investigate changes in the brain associated with aging.
For every hour of reduced sleep duration, the researchers found an incremental annual expansion of the brain ventricles and an annual incremental decline in global cognitive performance.
The age-related brain atrophy was seen in the ventricles, a series of interconnected, fluid-filled spaces in the core of the forebrain and brainstem. (A
"Though faster brain ventricle enlargement is a marker for cognitive decline and the development of neurodegenerative diseases such as Alzheimer's," the researchers say, "the effects of sleep on this marker have never been measured."
The research paper's results therefore add new evidence: "Each hour of reduced sleep duration at baseline augmented the annual expansion rate of the ventricles by 0.59%, and the annual decline rate in global cognitive performance by 0.67% in the subsequent 2 years, after controlling for the effects of age, sex, education and body mass index."
The study put 66 older Chinese adults through structural MRI brain scans that measured brain volume. They also had their cognitive function tested every 2 years using neuropsychological assessments.
A questionnaire was used to record the subjects' sleep duration. The participants came from the Singapore-Longitudinal Aging Brain Study, which has yielded evidence in numerous other published medical papers.
In the Sleep paper's conclusion, inflammatory effects were ruled out by the Duke-NUS authors: "In healthy older adults, short sleep duration is associated with greater age-related brain atrophy and cognitive decline. These associations are not associated with elevated inflammatory responses among short sleepers." The researchers checked this by measuring a marker of systemic inflammation, high-sensitivity C-reactive protein (CRP).
Optimal sleep duration
Lead author Prof. Michael Chee, an expert in cognitive neuroscience and behavioral disorders at Duke-NUS, has an idea of the optimal sleep duration. Prof. Chee says:
"Work done elsewhere suggests that 7 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."
The previous research on optimal sleep was reported in June 2013, using data from over 150,000 people from the brain-training company Lumosity, using its research platform, the Human Cognition Project.
Importance for aging populations
Prof. Chee told Medical News Today that his work aimed to fill a gap in the evidence on risk factors among aging populations. He hopes that results from future work will inform changes that could reduce disease.
"One of the challenges in persuading people to pay more attention to sleep," Prof. Chee said, "is that there is a gap between laboratory-based studies - which are small in sample size, short-term, but very detailed - and the epidemiological studies - which cover huge numbers of persons, but which can only study crude endpoints like death or disease, and pay less attention to intermediate outcomes like cognitive decline."
Prof. Chee also told MNT:
"Longitudinal studies seek to fill that gap, and we envisage that with Asia's very rapidly aging populations, cardio-metabolic problems like diabetes will just sky-rocket if attention is not paid to modifiable risk factors.
"The thing about such risk factors is that individually they make small, albeit significant, contributions - but over time, that effect matters."
The dangers of a lack of sleep were also highlighted in a paper in one of The Lancet journals - see Better sleep 'could be prescribed to treat metabolic disorders.'