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  • Writer's pictureNick Allen

Sleep regularity: the most important sleep variable?

In recent years, the role of sleep in health and performance has finally gained widespread recognition. The data is undeniable at this point that sleeping 7-9 hours per night is optimal for both cognitive function and the avoidance of disease. As this science has continued to evolve, however, some are now questioning whether there might be an even more important sleep metric to track than sleep quantity. Sleep regularity is a measure of the consistency of one’s sleep timing — someone with a high degree of sleep regularity will go to sleep and wake up at almost the exact same time every day, whereas someone with low sleep regularity will vary their sleep-wake times from one day to the next without any consistency.

When the first rumblings around sleep regularity began, I must admit that I was skeptical of the grandiose claims. Knowing the importance of the circadian rhythm in human physiology, I could have guessed that those with greater sleep regularity would have better outcomes. I was hesitant to believe, however, that this measure would have a stronger correlation with health and performance than sleep duration. Nevertheless, recent studies certainly seem to suggest that.

One of the most convincing studies on the topic, published in the journal Sleep just last month, looked at data from nearly 61,000 participants in the UK to evaluate sleep regularity and mortality for a nearly 8 year period. The results, summarized in Figure 1, show that both sleep regularity and sleep duration are linked with decreased mortality, though sleep regularity is the one with the more convincing relationship.

A deeper dive into this data suggests some key takeaways. Those in the top 20% by sleep regularity index (SRI) had a massive 30% lower risk of death than those in the bottom 20%. By comparison, the top 20% by sleep duration had a 24% lower risk of death compared to the bottom 20%. While both are clearly key metrics, SRI appears to be as important if not even more important than sleep duration.

Another interesting finding is that almost all of the mortality benefit from more sleep (higher sleep duration) seems to come from the avoidance of cardiometabolic disease. There were no statistically significant differences in cancer-related death or other causes of death across the various sleep duration groups. Contrast this with the sleep regularity groups, where those with the highest SRI had significantly lower risks of death from cardiometabolic disease, cancer, and other causes.

A lot of unknowns remain, but I’m fairly convinced that keeping a consistent sleep-wake schedule should be a priority for everyone. The health impacts are clear, but the benefits might not stop there. Though I haven’t seen any published data on this, there is certainly a belief in professional athletics that sleep regularity correlates strongly with peak performance. Anecdotally, I know that I feel notably better when my sleep schedule has been consistent for two weeks or longer. While we’ll continue to gather evidence about the extent of the benefits, I think there’s no reason to wait to prioritize this (potentially critical) aspect of your health.


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