Older adults who have too much, too little or restless sleep have an increased risk for Alzheimer's disease, according to studies that suggest doctors note these conditions in patients for follow-up evaluations.
The research, presented at the Alzheimer's Association International Conference in Vancouver, adds to increasing evidence that Alzheimer's and other disorders have early signs that can be caught by general practitioners.
About 5.4 million Americans have Alzheimer's and, by 2050, that number is expected to grow to as many as 16 million, according to the Alzheimer's Association. Without a cure in sight, health experts are looking for signs that may aid in early detection of dementia or help guide care.
"This is not exquisitely specific, but you think about things that can be used in a relatively normal physician's office setting," said William Thies, chief medical and scientific officer for the Chicago-based Alzheimer's Association. "It's not a diagnosis, but it's tracking a change where you think, gee, that's suspicious."
One study found that women who slept too much or too little had changes in their brains equivalent to aging two years. Another found that women with sleep apnea had twice the odds of developing a pre-Alzheimer's condition.
In the first report, from a subset of the Nurses' Health Study, 15,000 women age 70 and older were examined every other year for six years. In that study, researchers found that those who said they slept five hours a day or less had lower scores on tests of cognition than those who claimed to sleep seven hours. So did those who reported nine hours a day or more of sleep.
Changes in sleeping patterns by more than about two hours over the course of the study were linked to lower cognitive scores, according to the researchers, led by Elizabeth Devore, an instructor at Harvard Medical School and Brigham and Women's Hospital in Boston.
An analysis of 468 women in the study who gave blood samples found that those in the group who slept five hours a day or less or nine hours a day or more had abnormal levels of the Alzheimer's-associated beta amyloid. That requires further follow-up because there were so few women in it, Devore said.
"It's important for clinicians to start asking about sleep, because it's important for lots of outcomes, including cognitions," Devore said. Her results suggest more research should be done to determine how much women are actually sleeping, and if the women reporting long sleep durations were spending more time in bed without sleeping more, she said.
In a separate study of 1,300 women older than 75, scientists found that those with sleep apnea or sleep-disordered breathing had twice the odds of developing mild cognitive impairment, a pre-Alzheimer's disease condition. Sleep disturbances may be a sign doctors should send patients for neurological evaluations, said Kristine Yaffe, a study author and researcher at the University of California, San Francisco.
Yaffe's study found that over the course of five years, women who developed disruptions in their circadian rhythms, the mental and physical patterns that change over 24 hours, were at increased risk of developing mild cognitive impairment.
A third study, following almost 4,900 people over eight years, showed that risks of cognitive decline increased when patients had excessive daytime sleepiness. Increased difficulty maintaining sleep at night wasn't associated with the risk of cognitive decline, according to the researchers led by Claudine Berr of France's National Institutes of Health and Medical Research.