Sleeping for more than nine hours a night may be an early warning sign of Alzheimer's disease, US research suggests.
An inability to get out of bed may be a symptom rather than a cause of the brain changes that lead to dementia, according to new research published in the journal Neurology.
Researchers in the US found people who consistently slept for more than nine hours each night were twice as likely to develop dementia during the next 10 years as those sleeping nine hours or less.
Participants without a high school degree who slept for more than nine hours increased their risk sixfold, suggesting that education lessened the effect.
"Self-reported sleep duration may be a useful clinical tool to help predict persons at risk of progressing to clinical dementia within 10 years," lead research author Dr Matthew Pase said.
"Persons reporting long sleep time may warrant assessment and monitoring for problems with thinking and memory."
Another study found that developing rambling speech might also be an early indication of mild cognitive impairment, which can lead to Alzheimer's.
The new findings are based on data from more than 2400 patients enrolled in the Framingham Heart Study, a major US investigation into heart disease risk factors.
Participants, who had an average age of 72, were asked how long they typically slept each night and observed during a period of 10 years.
A total of 234 cases of dementia were recorded in the follow-up period.
"While unusual sleep patterns are common for people with dementia, this study adds to existing research suggesting that changes in sleep could be apparent long before symptoms like memory loss start to show," Dr Rosa Sancho from Alzheimer's Research UK said.
