The Telegraph – For many, the chance to have a lie-in most mornings is one of the luxuries afforded by retirement.
But according to new research, it could also be an early warning sign of Alzheimer’s.
Scientists studying a cohort of over-60s found that those who consistently slept for more than nine hours each night were twice as likely to develop the neurological condition as those who slept for less than nine hours.
Around 7 per cent of people over 65 develop Alzheimer’s or another form of dementia, and the risk is thought to double every five years people gain in age.
It is unlikely people will be able to reduce their risk by getting up earlier, however, as the researchers behind the new study said the inability to get out of bed is probably a symptom rather than a cause of the illness.
The Boston University team also found that those in the study without a high school degree who slept for more than nine hours increased their risk by a factor of six, suggesting education had a protective effect.
While it is currently impossible to halt or cure dementia, its onset can be slowed and patients helped to acclimatise to the condition if doctors know they are at risk.
Dr Matthew Pase, who led the research, said: “Persons reporting long sleep time may warrant assessment and monitoring for problems with thinking and memory.”
The new findings are based on data from more than 2,400 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 over a period of 10 years.
A total of 234 cases of dementia were recorded over the follow-up period.
Sleeping for more than nine hours more than doubled the risk of both all types of dementia and specifically Alzheimer's.
It was also associated with smaller brain volume.
Dr Rosa Sancho, from Alzheimer's Research UK, said: "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.
"Other studies have indicated a link between changes in sleep quality and the onset of dementia, and while this wasn't measured in this study, it could be an important factor affecting sleep duration.”
She added: "Understanding more about how sleep is affected by dementia could one day help doctors to identify those who are at risk of developing the condition.
Another study has found that developing rambling speech may be an early indication of mild cognitive impairment (MCI), which can lead to Alzheimer's. The new research is reported in the journal Neurology.