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Do Sleep Patterns Affect the Risk of Cognitive Decline?

Older CoupleVANCOUVER—The quality and quantity of sleep may be associated with the risk for cognitive decline, according to four studies presented at the 2012 Alzheimer’s Association International Conference. Treatments for insomnia or circadian rhythm delay might reduce or prevent cognitive decline, investigators reported.

Sleep Duration and Cognition
Compared with a sleep duration of seven hours per day, sleep durations of five or fewer hours per day and of nine or more hours per day were associated with worse average memory at older ages, according to Elizabeth Devore, ScD, Associate Epidemiologist at Brigham and Women’s Hospital in Boston. Short and long sleep durations at midlife and in later life were both associated with worse memory in later life.

Dr. Devore and her colleagues examined 15,263 women age 70 or older who had participated in the Nurses’ Health Study. The researchers performed one initial cognitive assessment and three biennial follow-up assessments of each participant. At baseline, the subjects reported sleep duration in midlife and in later life. The investigators used multivariable-adjusted mixed linear regression models to estimate mean differences in slopes of cognitive decline in several categories of sleep duration. Multivariable-adjusted linear regression was used to estimate mean differences in overall cognitive status at older age.

Women with sleep durations that changed two hours per day or more between midlife and later life had worse average memory at older ages, compared with those whose sleep duration did not change. “Regardless of where women started out in midlife, in terms of their sleep duration, the big changes seemed to be a problem for memory,” said Dr. Devore. “These findings indicate that extreme sleep durations or greater changes in sleep duration over time may contribute to cognitive decrements in older adults.”

Delayed Acrophase May Increase Risk of Dementia
People who experienced a shift in circadian rhythm acrophase had a risk of dementia nearly double that of people whose circadian rhythm remained stable, said Kristine Yaffe, MD, Professor of Psychiatry, Neurology, Epidemiology, and Biostatistics at the University of California, San Francisco. The finding was particularly true for patients whose shift was toward the later part of the day. Circadian rhythms that were not pronounced were also associated with an increased risk of dementia and mild cognitive impairment.
The results stem from Dr. Yaffe’s prospective study of 3,000 community-dwelling women. At enrollment, all participants were age 65 or older. At year 15, Dr. Yaffe and her colleagues assessed patients’ sleep parameters through actigraphy and polysomnography. Five years later, the researchers assessed patients’ cognitive outcomes through a battery of neuropsychologic tests. Patients’ clinical cognitive status was adjudicated.

Women with sleep-disordered breathing at baseline had nearly double the risk of developing dementia or mild cognitive impairment five years later, compared with women without sleep-disordered breathing. “It seems to be the hypoxia that’s related to risk of dementia and mild cognitive impairment, [not] the sleep fragmentation issue,” Dr. Yaffe commented.

This study may help explain why people with advanced dementia have alterations in their sleep–wake cycles, she added. “There may be some links between circadian shifts and amyloid-beta deposition in the brain. It may be possible that we could intervene and then delay, or somehow prevent, some of the cognitive sequelae.”

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