Without dispute, sleep is essential for physical and mental health. But sleeping excessively (more than 9 hours a night) may actually set you up for dementia and even make your brain smaller.
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. The study is significant as it is long-term (10 years) with nearly 2500 participants.
Past studies have suggested associations between both long and short sleep duration and an increased risk of dementia. However, the question remains whether 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, researchers at Boston University School of Medicine 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.
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.
Those who developed dementia also had a correlation with lower levels of education (lacking a high school degree).
“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,” said the lead researcher in a press release. “These results suggest that being highly educated may protect against dementia in the presence of long sleep duration.”
But is excessive sleep a symptom or a cause of dementia? The researchers suggest the former and that interventions to restrict sleep are unlikely to reduce the risk of dementia.