According to health recommendations, adults under age 60 should generally aim for between seven and nine hours of sleep each night, while those over 65 should average about seven hours, with a nightly maximum of eight. In reality, though, average sleep falls on a spectrum for most older adults, which can be impacted by a wide range of factors and can vary over time.
However, people on either end of the “sleep spectrum” – those who consistently get either too little or too much sleep each night – may face a common risk compared to those who land somewhere in the middle: faster rates of cognitive decline.
A recent large international study pooled two different groups that included a total of nearly 29,000 adults, most of whom were over 50. Participants reported information about their sleep habits in face-to-face interviews over 100,000 “person-years” of follow-up, and researchers regularly measured their global cognitive scores using a number of standard testing methods.
In both groups, global cognitive function for individuals whose average sleep duration was either extremely low (less than four hours per night) or extremely high (more than 10 hours a night) declined significantly faster than those in a reference group who averaged seven hours of sleep per night.
While the authors said their study clearly shows the relationship between sleep duration and cognitive decline, future research should focus on exactly how and why that decline occurs. “Ultimately, the study of sleep and cognition needs to go beyond sleep duration,” they added. “Both sleep quality and sleep quantity should be considered in developing prevention and management strategies for dementia.”