Turns Out, Too Much Sleep Might Mess With Cognition

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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."

This is by no means the first study to consider the link between sleep duration and cognition, and sleep patterns have previously been studied as potential markers of Alzheimer's disease.

The number we hear the most associated with sleep is eight hours, but does that really hold true? And if so—why did the researchers have the control group getting only seven hours of sleep?

Well, the amount of sleep we need is largely dependent on our age. This study included participants with an average age of approximately 61, which, according to the National Sleep Foundation (NSF), would mean they need anywhere from seven to nine hours of sleep per night.

Given the data from this new study, that range is still within the "safe" zone for preserving cognition—it's only the extremes of less than four or more than 10 that they call out as potentially damaging, though further specific study will be needed to confirm and explain these results.