Sleep 6.1 Intro to Sleep Regularity

An overview of why sleep regularity matters, its biological basis, health impacts, and how wearables and the Sleep Regularity Index (SRI) help measure it.

Video Breakdown:

00:00 Introduction to Sleep Regularity

01:06 Clinical Significance and Metrics of Sleep Regularity

06:13 Measuring Sleep Regularity with Wearable Data

So today's objective for the talk regarding sleep regularity is to answer these questions. Why has sleep regularity gained so much scientific and clinical attention recent years?
Why does sleep regularity matter for health and what biological mechanisms might explain its relevance? Which Sleep regularity metric should researchers use? And under what circumstances and what are the strengths and limitations for each? And how can sleep regularity be measured using wearable data, particularly consumer wearable data, which is gonna be the focus for Labfront particularly.
And I've divided sleep regularity into six categories here. The first one is intro to sleep regularity. I'll talk about clinical significance of sleep regularity, the physiological mechanisms, associated factors, the metrics, and also future directions as well. And so, traditionally the focus for sleep clinical care has been on sleep duration, and this is a result of well described relationships between sleep duration and key clinical outcomes.
This meta-analysis done by Yin in 2017 shows that U-shape or J-shape relationship between sleep duration and a number of key clinical outcomes all cause mortality, total cardiovascular disease events, coronary heart disease events and stroke events. And you could see that there's a sweet spot about six to seven to eight hours, where you have the lowest instance of mortality or these adverse events.
And then if you slept a little too little or too much that could be bad. This relationship at present appears to be correlational. It's unclear if it's causal because it could be that those individuals who have some predisposing conditions can actually sleep more or sleep less.
So it's unclear whether it's causal or correlational. But as a result of this emphasis on the sleep duration being important for these various key clinical outcome, public health has placed most of their energy on optimizing sleep duration. For instance, this is the American Heart Association's life's essential eight.
You could see it outlined here, eating better, being more active, quitting tobacco, managing your weight, controlling cholesterol, managing blood sugars, and managing your blood pressure and get healthy sleep. But when they talk about getting healthy sleep, this is the actual depictions that they show on their website.
Adults should aim for an average of seven to nine hours and obviously it depends on the age. But we have recognized that sleep is a multidimensional construct, which was proposed by Dr. Dan Buysse at University of Pittsburgh, which not only includes sleep duration, but also sleep efficiency, like how effectively one sleeps often incorporating information on sleep stages.
We're interested in sleep timing, the chronological aspects of when sleep occurs, and you might incorporate circadian rhythm within this category too. Then there's sleep regularity and then sleep satisfaction. The subjective measures of how restorative sleep feels to the individual. And daytime alertness, another qualitative measure, assessing cognitive function during the waking hours.
So the question is, what is sleep regularity? Basically it's just the consistency of sleep wake patterns from one day to the next. And this is depicted using a, raster plot. And raster plot just visualizes the time that you're asleep from day to day. This is obviously an idealized version, a high sleep regularity where a person sleeps exactly the same time, and then wakes up at the same time. A low sleep regularity you can imagine has a lot of variability and the timing of when a person goes to sleep, what time they wake up. And there could be fragmentation too, a lot of times when they're awake in the middle of the night.
This sleep regularity topic, has really become a hot topic. And if you've gone to any of the sleep research meetings, there's a buzz about it, especially in the last few years, and there's a number of reasons why.The first one is that there was an SRI or the Sleep Regularity Index, which was developed by Dr.Andrew Phillips during his time at Brigham Women's and Harvard Medical School and published in 2017. And this exact same SRI index was subsequently incorporated into large epidemiological studies such as the MESA or the multi-ethnic study of atherosclerosis and published in 2018. That study showed irregular sleep patterns as documented by this SRI index was associated with increased cardiometabolic risk factors such as obesity, hypertension, fasting glucose levels, and hemoglobin A1C. Then the big study that got a lot of press was the one published by the Phillips Group. Dan Windred is the first author.
They incorporated the SRI index in the UK Biobank and that showed that sleep regularity was actually a stronger predictor of all cause mortality than sleep duration. And then there are some follow-up studies just this year, again using the SRI index done by Andrew Phillips and again, applying to UK Biobank, but this time focusing on dementia incidents.
And it showed that sleep irregularity had a dose response correlation with dementia incidents, and all of this received a decent amount of attention in the news. And also the National Sleep Foundation put out the consensus statement in 2023, which we'll talk about later, which truly emphasized the importance of sleep regularity.
The other additional component for why sleep regularity has become popularized is because it's actually become much more accessible, and that has to do a little bit with the wearables that are enabling this. And this is actually the data that we generate through our Labfront app and incorporating our Garmin Vivosmart 5 and this shows a raster plot of an individual over a span of four weeks.
You could see the sleep period that are demarcated using our sleep actigraphy methodologies. And you could see the amount of irregularity here as well. And there's also availability of open source analytics such as the GGR package, which is the R package and the sleep rank package made available by Dan Windred who did that major publication with the UK Biobank. There's also a Python version of this as well. And so both these things had made sort of sleep regularity increasingly accessible to researchers.

Course episodes

Sleep 6.1 Intro to Sleep Regularity

Sleep 6.2 The Clinical Importance of Sleep Regularity

Sleep 6.3 Physiological Mechanisms of Sleep Regularity

Sleep 6.4 Exploring the Factors Influencing Sleep Regularity

Sleep 6.5 Understanding Sleep Regularity Metrics

Sleep 6.6 Future Innovations in Sleep Monitoring