NEW YORK - With less sleep, normal aging-related structural changes in the brain progress slightly faster in middle-aged and older people, according to a new brain imaging study.
Sleep troubles are more common with age, and shrinkage of certain brain structures is normal. But for the over-55 study participants, those changes could be seen accelerating slightly with each hour less of sleep each night.
"Among older adults, sleeping less will increase the rate their brain ages and speed up the decline in their cognitive functions," said lead study author Dr. June Lo, a researcher with Duke-NUS Graduate Medical School in Singapore.
Plenty of past research has shown that lack of sleep can worsen fuzzy thinking and memory problems in the short term, and at all ages, Lo and her colleagues note in the journal Sleep.
"Our lab has also shown repeatedly in the past decade that in young adults, brain and cognitive functions are affected when people do not have enough sleep," she told Reuters Health in an email. "As a result, we wanted to know whether sleeping less would affect brain and cognitive aging in older adults."
Fewer studies have looked at physical changes in the brain and their link to sleep over time, the report points out. And none have done it for older adults, according to the researchers.
To assess the effects of sleep duration on both thinking and brain structure, the study team analysed data on healthy people over age 55 participating in the larger Singapore Longitudinal Aging Brain Study.
Lo and her colleagues looked at data on 66 Chinese adults who had previously undergone magnetic resonance imaging (MRI) scans to measure brain volume in specific areas and had taken tests to assess their cognitive skills.
The researchers used questionnaires to determine participants' sleep duration and quality, and measured blood levels of high sensitivity C-reactive protein, an indicator of inflammation.
When the cognitive tests and scans were repeated two years after the initial round, the researchers found those participants who slept fewer hours showed evidence of faster brain shrinkage and declines in cognitive performance.
The ventricles are fluid-filled spaces in the brain, and they expand as the brain ages, indicating a shrinkage of brain tissue. Faster ventricle enlargement is a marker for cognitive decline and the development of neurodegenerative diseases such as Alzheimer's, according to the authors.
For each hour less participants slept, on average, the rate of ventricle enlargement rose by 0.59 per cent, after adjusting for other individual factors like weight, age, sex and education.
And for each hour less of sleep, the decline in cognitive performance increased by 0.67 per cent - though the researchers caution that result was more variable and should be considered preliminary.
Lo and her colleagues found no links between inflammation and sleep duration or cognitive decline. Nor was sleep quality linked to the brain changes.
The study cannot prove that total sleep time caused the changes observed. Although the study subjects were free of any major diseases or diagnoses, the researchers did not determine, for example, if other factors that might affect both brain structures and sleep duration could account for the results.
The reasons why shorter sleep time might affect brain changes are still a bit of a mystery, Lo said, but there are several possible mechanisms.
"Some have proposed that sleep loss increases inflammation which has a negative impact on the brain, but our own data do not support this view," she said. "Alternatively, short sleep is associated with other medical conditions which may accelerate brain aging."
Dr. William Kohler said that although the new study was small, it was interesting and makes sense overall. Kohler, who was not involved in the study, is medical director of the Florida Sleep Institute.
He said that studies on mice suggest one possible mechanism may be that sleep removes wastes from the brain.
"If one of the purposes of sleep is to remove toxic products, then if those products aren't removed because you're not getting enough sleep, you're going to be more likely to develop cognitive problems and degeneration later on," he said.
Kohler added that as we age, our sleep mechanisms weaken so it's harder to get to sleep, but there are things people can do to improve sleep.
"Avoid napping during the day, have a firm routine as far as going to bed at the same time, get up at the same time and try to ensure that we get to sleep by following good sleep hygiene techniques," he said.
Kohler suggested that the environment should be dark and quiet enough for sleep and that the mattress should be comfortable. In addition, he suggested avoiding alcohol, cigarettes and exciting activities close to bedtime.
"Many people think that sleep is something you can sacrifice if you have work to do, a game to watch, etc.," Lo said. "Therefore, insufficient sleep is so common that CDC has announced this as a public health epidemic."
She added that people should understand sleep is crucial for many physiological functions, such as cell repair and memory consolidation.
"Knowing that there are negative health consequences of sleep loss may motivate some to sleep more," she said. "Having good sleep hygiene and habits may improve the amount and quality of sleep."