Excess sleeping is an 'early symptom' of Alzheimer's
Sleeping for more than nine hours a night could be an early warning sign of Alzheimer's, new research suggests.
Scientists believe an inability to get out of bed may be a symptom rather than a cause of the brain changes that lead to dementia.
For this reason, simply reducing the length of sleep time is unlikely to reduce a person's risk.
Researchers in the US found that people who consistently slept for more than nine hours each night were twice as likely to develop Alzheimer's or other forms of dementia over 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 six-fold, suggesting that education lessened the effect.
Lead author Dr Matthew Pase, from Boston University medical centre, said: "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."
The research is reported in the journal Neurology.