Is sleep regularity more important than sleep duration? • Stronger by Science

You’ve likely heard the classic sleep advice: “Make sure to get 7-9 hours of sleep.” You may have also come across content, or even books, that highlight the importance of 7-9 hours of sleep and how anything short of that can be catastrophic to your health, performance, and body composition. However, recent research suggests that sleep duration is not the only factor to focus on when it comes to your sleep routine. It turns out that sleep regularity, meaning how consistent your sleep and wake times are, may be more important for overall health and longevity than sleep duration.

A recent study by Windred et al (2024) analyzed over 10 million hours of accelerometer data from nearly 61,000 adults and found that people with the most regular sleep schedules had a ~20-50% lower risk of dying from any cause compared to those with the least regular sleep. Sleep regularity was quantified using the Sleep Regularity Index (SRI), which measures the probability that an individual is in the same sleep or wake state at any two time points exactly 24 hours apart, across a 7-day period. SRI scores were calculated using one week of data collected from wrist-worn accelerometers and processed with GGIR, an open-source R package for estimating sleep–wake states from raw accelerometry. These outputs were then passed to sleepreg, a custom R package developed by the authors to compute SRI. It accounted for sleep-wake patterns, naps, sleep fragmentation, and variations in sleep timing. Valid SRI scores were computed for participants with at least 5 days of quality data, after excluding device non-wear and erroneous recordings.

I know this is all very technical, but I wanted to highlight how this piece of research differs from some common sleep duration studies that rely on self-reported questionnaire data. I also find it quite refreshing that the software used by the authors is open-source and available for anyone to use, or even modify. Yay #openscience.

However, let’s return to the study and its findings. Interestingly, when sleep regularity and sleep duration were compared head-to-head as predictors of mortality, sleep regularity was a better predictor of all-cause mortality. While sleeping too little or too much showed a relationship with mortality, similar to previous research, the consistency of sleep-wake times was a stronger and more reliable predictor. These associations held even after adjusting for age, sex, physical activity, socioeconomic status, health conditions, and mental health.

To put the participants’ sleep regularity in perspective, participants in the top 20% for sleep regularity had bedtime and wake-up times within a 1-hour window each day, while those in the bottom 20% had bedtime and wake-up times within a 3-hour window each day. 

Although it seems like a wise approach to prioritize maintaining a consistent sleep schedule, sleep duration still matters. In this study, individuals who slept for only 5-6 hours had an increased mortality risk, with the lowest risk generally observed in individuals who slept around 7.5 hours and maintained a consistent sleep schedule.  Another interesting insight from the study is that irregular sleep appeared to be especially harmful for cardiometabolic and cancer-related mortality. This may be due to how inconsistency disrupts your circadian rhythm, which can influence everything from hormone production to immune function. 

Overall, aiming for ~8 hours of sleep is still a solid approach as far as sleep duration goes but it’s worth keeping in mind that as long as you’re going to sleep and waking up roughly within the same 1-hour window, getting a bit less sleep here and there is likely not going to have a huge impact on your overall health. 

If you want to learn more about sleep, make sure to check out our 2-part episode on the SBS podcast, where we cover everything sleep-related: Part 1 and Part 2.