How could something that feels so good - a long night's sleep - have negative consequences? Unfortunately, that is one possibility that results of a new study suggest: Older adults who sleep nine or more hours each day may have a higher risk of developing dementia than those who spend fewer hours in bed.
Spanish researchers found that among nearly 3,300 older adults they followed for three years, those who slept nine or more hours per day, daytime naps included, were about twice as likely to develop dementia as those who typically slept for seven hours.
These "long sleepers" were at increased risk even when the researchers accounted for several factors that can affect both sleep and dementia risk -- including age, education, and smoking and drinking habits.
Still, the findings show only an association between longer sleep and dementia, and do not prove that extra hours in bed, per se, contribute to mental decline.
"It remains to be established how the relation between longer sleep duration and dementia is mediated," Dr. Julian Benito-Leon, of University Hospital '12 de Octubre' in Madrid, told Reuters Health in an email.
One possibility, according to Benito-Leon, is that increased fatigue and sleep is an initial sign of early dementia in some people.
Another theory is that one or more underlying health problems may increase older adults' need for sleep, as well as contribute to dementia. The breathing disorder sleep apnea, for instance, causes fatigue and has been linked to impairments in thinking and memory in older adults.
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