By: Terri Petkau, PhD

Sleep is important for health and longevity – this is something that is already well-established. Significant research has gone into determining how much sleep is optimal for your health, with recommendations settling around 7-8 hours for most people. However, a 2024 study by Windred et al. published in the journal Sleep draws attention to the fact that duration is not the only metric we can measure, and perhaps not even the most important. In this study, sleep regularity is shown to be an important predictor of mortality risk, and in fact, an even stronger predictor than sleep duration.

What did the researchers do? Windred et al. relied on information from the UK Biobank, from which they were able to obtain data for 60,997 participants aged 40-69. Participants included in this study wore devices that collected accelerometer data on their dominant wrist for 7 days. The researchers then used a metric for measuring sleep regularity – called the Sleep Regularity Index (SRI) – which they had developed previously. The SRI uses accelerometer data to compare sleep regularity from one day to the next. The SRI calculation accounts for naps, fragmented sleep, and large periods of wake during sleep, as well as days when the participant did not wear the device. Based on the calculated SRI, participants for the current study were grouped into quintiles – SRI scores of 0-20 (lowest sleep regularity), 21-40, 41-60, 61-80, and 81-100 SRI (highest regularity sleep). The researchers then asked the question: Compared to the lowest quintile group for sleep regularity, is the risk of all-cause mortality significantly different in individuals whose SRI is higher?

What was the key finding? Compared to the lowest scoring group (0-20 SRI), the risk of all-cause mortality over an 8-year follow-up period decreased for every SRI group with a higher score (see Figure 1); in other words, every progression towards more regular sleep patterns lowered the risk of all-cause mortality. Sleep duration also predicted risk of all-cause mortality, but not as robustly as sleep regularity.

What else can we see in the data? We can see that the lowest quintile group for sleep regularity has a considerably higher mortality risk than any of the other 4 groups.  Further to that, we see that the lowest sleep regularity group had the broadest range of scores – the group is composed of individuals whose SRI ranged from 2.5 – 71.6 (on a scale of 0-100), while the other 4 groups had much tighter ranges. It is possible that the relatively high mortality risk in the lowest group is driven by a few individuals with very poor sleep regularity; a closer look at the data would be required to determine whether or not this is the case.

What are the main takeaways? From a scientific perspective, this study has enough caveats to preclude firm conclusions about the relative importance of sleep regularity vs. sleep duration. Aside from the potential bias in the data as noted above, the study is also limited by low ethnic diversity in the study population (which reduces our confidence in the general applicability of the findings) and the fact that it is a study of association, not causation. Further research is needed to better understand the relationship between sleep regularity and long-term health outcomes. From a health perspective, however, if you have the opportunity to make your sleep more regular (even if you don’t sleep for longer), do it! You won’t be doing any harm and you may well be making a contribution towards your overall health and long-term well-being.

Article citation:

Daniel P Windred, Angus C Burns, Jacqueline M Lane, Richa Saxena, Martin K Rutter, Sean W Cain, Andrew J K Phillips, Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study, Sleep, Volume 47, Issue 1, January 2024, zsad253,  https://doi.org/10.1093/sleep/zsad253