Sleeping for more than nine hours each night may predict the risk of developing dementia, and people who sleep a lot tend to have smaller brains.
Those are among the findings in a new study, “Prolonged sleep duration as a marker of early neurodegeneration predicting incident dementia,” that appeared recently in the journal Neurology.
Evidence from past studies have hinted at associations between both long and short sleep duration and an increased risk of dementia. However, it remains unclear if sleep duration is a risk factor or a marker for dementia.
Sleep may provide a restorative function, removing metabolic waste from the brain and preventing accumulation of the amyloid protein, a hallmark of Alzheimer disease (AD). On the other hand, sleep disorders may also emerge as a result of atrophy of brain regions involved in sleep and wakefulness, or as a consequence of mood disturbances, which are common in dementia.
To evaluate the association between sleep duration and the risk of incident dementia and brain aging, Sudha Seshadri, MD, neurology professor at Boston University School of Medicine and his colleagues evaluated sleep duration in 2,457 adults taking part in the Framingham Heart Study.
Participants told researchers how long they typically slept each night. The researchers then observed them for 10 years to see who developed Alzheimer’s disease and other forms of dementia. Over the 10-year period, 234 patients developed all-cause dementia. Researchers then linked prolonged sleep duration with a higher risk of incident dementia; their findings were largely driven by people with baseline mild cognitive impairment as well as those without a high-school degree.
They also discovered links between longer sleep periods and both smaller cerebral brain volume and poorer cognitive function, and suggested that screening for sleeping problems may help detect such cognitive impairment and dementia.
“Participants without a high-school degree who sleep for more than nine hours each night had six times the risk of developing dementia in 10 years compared to participants who slept for less,” Seshadri said in a news release. “These results suggest that being highly educated may protect against dementia in the presence of long sleep duration.”
The findings indicate that excessive sleep may be a symptom rather than a cause of the brain changes that occur with dementia. In this context, researchers suggest that interventions to restrict sleep are unlikely to reduce the risk of dementia.
“Self-reported sleep duration may be a useful clinical tool to help predict persons at risk of progressing to clinical dementia within 10 years. Persons reporting long sleep time may warrant assessment and monitoring for problems with thinking and memory,” said Matthew Pase, PhD, fellow in the neurology department of Boston University School of Medicine.