Using data from two long-term population studies on aging (the English Longitudinal Study of Ageing and the China Health and Retirement Longitudinal Study), the researchers behind this new paper pooled a group of over 28,000 individuals to establish the link between “extreme sleep patterns” and cognition over time.
The participants reported their nightly sleep duration and participated in a series of cognitive tests, including immediate and delayed recall tests and fluency tests.
Researchers found that over time, participants who slept less than four hours or more than 10 hours a night experienced more rapid mental decline than a control group, who were getting seven hours of sleep each night.
According to the paper, this suggests that “cognitive function should be monitored in individuals with insufficient (≤4 hours per night) or excessive (≥10 hours per night) sleep duration,” though the team acknowledges that “future studies are needed to examine the mechanisms of the association between sleep duration and cognitive decline.”
The exact mechanism by which sleep patterns impact cognition needs to be researched further, but the paper does refer to a 2016 study that found that getting more or less than seven hours of sleep was linked to the thinning of cortical region of the brain, even in adults with normal cognition.