The Right Amount of Sleep for Stable Cognition in Older Adults

The wonders of sleep. What a good night's sleep can do for our resistance to stress, memory, and creative insight. Some famous discoveries are even said to have come in dreams – the Scientific Method supposedly came to Rene Descartes in a dream. But as we age and our sleep requirements change, is there a certain amount of sleep, a so-called sleep sweet spot, that allows our brains to work more efficiently and stave off cognitive decline? 

Researchers from the Knight Alzheimer Disease Research Center at Washington University published a new study in the journal Brain investigating the link between sleep duration and cognitive functioning to determine if sleep could be a potential marker for Alzheimer's disease progression. The study's lead researcher, Brendan Lucey, MD, MSCI, had found in earlier investigations that poor sleep quality was associated with early signs of Alzheimer's. 

This current study, a longitudinal study of 100 older adults, examined participants' sleep-wake activity over 4 to 6 nights with an EEG device. Participants completed annual cognitive testing for obtaining the Preclinical Alzheimer Cognitive Composite (PACC) score, and Alzheimer's disease markers – tau and amyloid-B42 – were measured in each participant's cerebrospinal fluid (CSF). Most participants had a clinical dementia rating of 0 at baseline, meaning they had no cognitive impairments. CSF results correlated with dementia ratings from testing.

Study results showed that older adults who slept between 4.5 and 6.5 hours a night had more stable cognitive function over time, while those who slept less than 4.5 hours or greater than 6.5 hours experienced significant cognitive decline over time, even when accounting for confounders of age, years of education, sex, and APOE genotypes (some APOE gene variants are associated with an increased risk of Alzheimer's disease).

With more details uncovered on the relationship between sleep and cognition, researchers hope study results can be used clinically when providers make recommendations to their older patients on sleep guidelines for maintaining optimal cognitive functioning.