11 October 2012

Sleep fragmentation tied to risk of Alzheimer's disease

Older adults who had the most fragmented sleep over a 10-day period were more likely to develop Alzheimer's disease than less-fragmented sleepers.

Older adults who had the most fragmented sleep over a 10-day period were more likely to develop Alzheimer's disease than less-fragmented sleepers, researchers say.

Their work, part of the Rush Memory and Aging Project, was presented at the American Neurological Association Annual Meeting in Boston. The lead researcher said the findings are consistent with animal studies that showed long-term disruption in sleep led subjects to develop Alzheimer's pathology more rapidly - but they're still a long way from having significant clinical implications.

How the study was done

Dr Andrew Lim, a neurologist from Sunnybrook Health Sciences Center in Toronto, Canada, and his colleagues took actigraphy measurements for 734 elderly adults (mean age, 81.6; 76% female) over 10 days.

During a mean follow-up of 3.3 years, 96 people developed Alzheimer's disease. The researchers found that being one standard deviation above the mean for rest and activity fragmentation was associated with a 21% and 26% increased risk of Alzheimer's disease, respectively.

In linear mixed effect analysis, rest and activity fragmentation were linked to faster cognitive decline (p = 0.037 and p = 0.003, respectively).

"One possible explanation is that individuals who are sleep-fragmented at baseline already have something wrong with them. (Sleep fragmentation) may be a marker of underlying pathology already," said Dr Lim.

"But of course the more exciting possibility, and the possibility that's raised by the animal work as well, is that sleep fragmentation or sleep disruption itself is harmful in terms of the underlying pathological processes of Alzheimer's disease, or the converse, that getting a good night's sleep may in fact be protective," he said.

Degree of variability

Dr Lim said there was some degree of variability in rest fragmentation from one night to the next among participants - so future studies should look at actigraphy readings over a longer period of time.

Eventually, he said, researchers may try to intervene in people with fragmented sleep, with the aim of decreasing their risk of Alzheimer's. But that depends on the outcomes of future mechanistic animal studies.

Dr Kristine Yaffe, a psychiatrist and director of the University of California, San Francisco Dementia Epidemiology Research Group, said basic science has suggested extended loss of sleep may lead to greater build-up of amyloid beta in rodents.

"We've had an accumulating body of evidence both from basic science and clinical studies like this that are showing us that there clearly is a connection between the sleep quality and prospective risk of developing dementia," said Dr Yaffe, who wasn't involved in the new study. "There's lots of converging data."

Still, she agreed more research is needed to hone in on the mechanism behind the potential link.

But until then, it never hurts to ask about sleep, researchers said.

"This raises the question for anybody who takes care of older individuals of asking about sleep, and identifying sleep problems and treating them, with the idea that potentially it may be a risk factor for developing Alzheimer's disease," Dr Lim said.

(Reuters Health, October 2012)

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