A paradox of the modern world is that we undervalue and deprioritize things we know to make us healthier, happier and more productive. Sleep is chief among them.
The research is unambiguous: Good Sleep is a powerful performance enhancer. With Good Sleep, we’re stronger, we’re smarter, and we look better. Everything we want to accomplish–physical goals, cognitive goals, relationship goals–becomes easier.
Going through the world with Bad Sleep is running a marathon with a weight vest on. Yet not sleeping has become a badge of honor. Imagine athletes bragging about their poor preparation and lack of training. Would we ever imagine they were in the best position to perform well? The same goes for sleep, for athletes and non-athletes alike.
The fact that we’re unconscious for a third of our lives provides a hint to the importance of sleep. It’s hard to think of a worse evolutionary disadvantage than conking out for a third of each day, prone to attack, and unable to find food. In spite of that cost, humans evolved to require a huge amount of sleep, something we fail to appreciate as a society.
Sleep Environment
Environment plays a prime role in sleep quality. You wouldn’t try to study at a construction site, and you wouldn’t try to PR your 10K in 10 degree weather, so why sleep in an environment not conducive to optimal sleep?
I can only speak for myself, but I think the optimal sleep environment differs for everyone. Over the years, I’ve experimented with different set-ups and gadgets, and have landed on a core “Sleep Stack” to create the optimal sleeping environment. I sleep best in a room that’s very cold, pitch black, with white noise.
Cold
If I could choose one characteristic of an optimal sleep environment, it would be temperature somewhere between 62-65 degrees. Sleeping in a warm room is a slow drip IV of discomfort, so I avoid it at all costs.
Central AC is rare in San Francisco, so the tools of choice are a bedroom AC unit and Chili Pad. The Chili Pad goes under the sheet, and circulates cold water, keeping your sleep surface as icy as you want. The first night you sleep with the Chili Pad, you wonder how you ever slept without it.
Dark
Our circadian rhythms follow the pattern of the sun. We’re awake when it’s light, we sleep when it’s dark. I’ve found that any light shining through in the morning impacts my ability to sleep optimally.
I’ve tried numerous black out curtains and have slept in loads of hotels with heavy-duty curtains, but nothing has blocked light as well (and at as low of a cost) as overlapping black towels.
If you can get past your significant other tolerating the eye-sore, this is highly recommended.
When I’m on the road and don’t have black towels blocking all the light, I use this sleep mask, which works well.
White Noise
For some reason, sleeping in dead silence is uncomfortable and my mind seems to wander more. To create some white noise, I blast a fan, with the air pointing in the opposite direction.
Blanket
My most recent acquisition is the Gravity Blanket, a 35 lb blanket that’s insanely cozy and meant to make you feel peaceful and comforted. I’ve only had it for a few weeks, but I’ve enjoyed it so far.
Sleep Tracking
I’ve been tracking my sleep on and off since 2013, originally with the (now defunct) Zeo and for the last year and a half, with the Oura ring.
There are a lot of devices that track sleep, but I enjoy the Oura ring because I don’t love wearing watches (to be fair, I don’t love wearing rings either, but this is the lesser of two evils). I’m less interested in non-wearable sleep trackers, because I think heart rate and heart rate variability are really important metrics to track, which non-wearables don’t get, or don’t get as accurately.
Tracking sleep nightly has several benefits for me. First, it’s a forcing function to do the things that lead to better sleep, knowing I’ll see the results in the morning. Second, it builds up a dataset that’s useful in seeing trends over longer time-horizons.
ROI
These things aren’t cheap. The combined cost of these items is over $1,000, but I look at them as investments, not expenses. If you could guarantee me a 10% increase in the length and quality of my sleep for the next year, the return on investment in the form of increased health, happiness, and productivity would be higher than any other investment I could make.
Analysis
I’ve collected 464 nights of sleep data from the Oura ring. The nights I’ve missed have been a combination of either forgetting to put it on, or a depleted battery. The missed nights seem to be distributed randomly, and shouldn’t skew the dataset.
Oura records a lot of metrics (full list here), but the ones I track most closely are total sleep, deep sleep, REM sleep, sleep efficiency, bedtime, heart rate, heart variability, and respiratory rate (breaths per minute).
Over the last year and a half, these are my nightly averages:
Takeaway 1: Get more overall REM sleep, and increase my REM:Total Sleep ratio
My REM:Total Sleep ratio is currently 19%. Studies suggest 20%-25% to be optimal, so getting an extra 25 minutes of REM sleep a night would get me to a 25% REM:Total ratio, assuming the same amount of total sleep. More on this below.
Takeaway 2: I can get more total sleep without spending more time in bed
Increasing sleep efficiency (total sleep / total time in bed) from 88% to 93% would give me an extra “free” 20 minutes of sleep a night. That’s an extra 2h 20m a week, or 121h 40m in a year. That’s 5 full days worth of sleep a year by tossing and turning less, and spending 0 additional minutes in bed. Seems worth pursuing.
Correlations
I’ll start by looking at correlations across the entire dataset. The chart below highlights the correlation coefficients between different metrics. The size and intensity of the colors reflect the intensity of the correlation. Blue marks high positive correlation, where an increase in one metric is correlated with an increase in the other; red marks high negative correlation, where an increase in one metric is correlated with a decrease in the other.
Obligatory correlation ≠ causation note here. A lot of these correlations are simply results of other behaviors. For example, take the correlation between Bedtime and Heart Rate. I don’t believe going to bed later inherently increases my heart rate. But on nights when I go out and have drinks, I tend to go to bed later, and the drinking increases heart rate.
Takeaway 1: REM sleep is highly correlated with Total Sleep
Shorter nights of sleep disproportionately impact REM. This is an important point. Because more REM occurs later in the sleep cycle, a night with 80% of normal sleep doesn’t impact all phases of sleep by 80%. It disproportionately crushes REM, which impacts our ability to concentrate, skill acquisition, problem-solving, and other things most of us need to function in the modern world.
Takeaway 2: Total Sleep is highly negatively correlated with Bedtime
This confirms what I’ve always felt: if I go to bed later than usual, I still wake up around the same time and have less overall sleep. Because my circadian rhythm is so early, I try hard to go to bed early every night, knowing I won’t get a full night of sleep otherwise. In my ideal world, my sleep schedule would be something like 9pm-5am. Early mornings with no one awake yet are special times, and when I do my best thinking.
Takeaway 3: Heart Rate Variability is highly negatively correlated with Heart Rate
You can read more about the importance of Heart Rate Variability here, but it serves as a great proxy for stress levels, recovery, and readiness to perform. I don’t think Heart Rate directly impacts Heart Rate Variability, rather the things that lead to an increased heart rate–drinking, late workouts, stress–can crush Heart Rate Variability and our ability to perform at peak performance.
Takeaway 4: REM is positively correlated with Breaths Per Minute, and negatively correlated with HRV
I don’t know what to make of this. An increase in BPM is negatively correlated with sleep efficiency, deep sleep, and heart rate–all bad outcomes. Not surprising, given that the things that reliably make my BPM increase are drinking and eating a big meal close to bedtime.
So why the positive correlation with REM? Could it be that a late meal increases my BPM, but is stress-reducing which lets me get more REM?
I’m also not sure why REM negatively correlates with HRV. I’d assume the things that lead to high HRV–good workouts, good sleep, lower stress–would also increase REM. Something to explore more.
I’ll stop here for now, but in Part 2, I’ll dive into how the schedule and travel of an MLB season affected my sleep, what I learned from the data, what I’d do differently, and what sleep experiments I’ll be running this year.