Improving sleep patterns may help reduce cognitive decline in older adults, and the ideal amount of sleep for good cognition appears to be six to nine hours per night. So suggest findings of a large study led by researchers at the University of Oregon (UO) and published in the June issue of the Journal of Clinical Sleep Medicine. Results confirm those of previous smaller studies.
"We wanted to look at aging, particularly dementia and cognitive decline as people get older, and the importance of sleep," says lead author Theresa E. Gildner, a doctoral student in the UO's anthropology department. “Our results provide compelling evidence that sleep matters a lot.”
The researchers compiled data across six middle-income nations and involving more than 30,000 people for a long-term project (the Study on global AGEing and adult health, or SAGE) that began in 2007. The journal article is based on the first wave of data from the project and focuses on people 50 years old and older in China, Ghana, India, Mexico, the Russian Federation and South Africa.
"In all six countries, which are very different culturally, economically and environmentally—despite all these differences—you see similar patterns emerging," Gildner says.
Study participants rated their sleep quality on a five-point scale and also shared the number of hours they had slept over the two previous nights. Participants then underwent five standard cognitive tests involving immediate recall of a list of presented words, delayed recall of those words later, forward and backward recall of long lists of numbers, and a verbal fluency test in which they listed as many animals as possible without repetition, the use of proper nouns or descriptors. Those who had less than six hours or more than nine hours of sleep per night had significantly lower cognitive scores compared with others. Sleep quality mattered, too.
The findings have important implications for future intervention strategies for dementia, the researchers conclude. The consistent associations between intermediate sleep durations, high sleep quality and enhanced cognitive performance in these diverse populations suggests that improving sleep patterns may help reduce the level of cognitive decline as seen in older adults.
Co-authors with Gildner were J. Josh Snodgrass, PhD, an UO professor of anthropology; Melissa A. Liebert, an UO anthropology doctoral student; Paul Kowal, PharmD, of the World Health Organization (WHO) in Geneva, Switzerland, and the University of Newcastle Research Center on Gender, Health and Aging in Australia; and Somnath Chatterji, MD, of WHO. Funding for the research comes from the National Institute on Aging of the National Institutes of Health (NIH) as well as the NIH.