In my original sleep analysis, I highlighted my REM sleep and sleep efficiency as two areas to improve. Unfortunately, when it comes to improving either, an internet search returns a deluge of articles with generic advice and no data backing up their claims.
To try to get to an answer of what actually works, I’ll run a handful of sleep experiments over the coming months. I decided to start with cold showers because (a) I like them (b) they’re easy and cheap and (c) there is some evidence that they have health benefits.
It turns out that quarantine is the best time we’ll ever get to conduct self-experiments because almost every day is the same, limiting the number of variables between the control and intervention periods.
The Experiment
My experiment was dead simple: 3 weeks of normal sleep, followed by 3 weeks with a cold shower every night within 90 minutes of bedtime. The showers, which were as cold as my shower would go, lasted between ~3 to ~10 minutes, but I didn’t time them every night, and didn’t use the duration in this analysis.
I tracked my sleep with the Oura ring, which you can read more about in my last sleep post. I’m a fan of the ring because it’s non-invasive, holds a decent charge, and provides quick feedback on the main things I care about.
One night I forgot to take a shower, and another I forgot to charge my Oura, so I ended up with 19 nights of sleep data.
As far as I could tell, I had similar exercise, diet, stress, caffeine intake, and schedule during the Cold Shower and non-Cold Shower periods, but didn’t track most of this.
Cold Showers
There’s a masochistic element to cold showers. The first 15 seconds suck, but they’re unbelievably invigorating and have an immediate positive impact on my mood, at any time of day.
There is some science behind cold showers. If you’re interested in the details, this is a good meta-analysis of various studies. Among the potential effects: short-term increases to noradrenaline and dopamine, increased well-being and decreased anxiety, antidepressant effects, and immunity boosting.
Whether any or all of these purported benefits are true, it’s hard to deny the subjectively great feeling when hopping out of a cold shower or plunge.
Results
My total sleep was impacted the most, up 30 minutes during the Cold Shower experiment. My Deep Sleep remained unchanged, while I saw a 13% boost to REM Sleep for an extra 10 minutes of REM sleep a night. While my REM Sleep:Total Sleep ratio was largely unchanged (18% → 19%), I’m happy about any increase in overall REM.
Sleep Efficiency
In addition to REM, I’m most interested in increasing my sleep efficiency so I can spend the same amount of time in bed, while getting more sleep. I was happy to see a bump from 90% to ~93% during this experiment.
Recovery
I’ve spent less time focused on recovery metrics like Resting Heart Rate and HRV, but it was encouraging to see the positive impact cold showers had on both of these metrics. My RHR was almost a beat and a half lower, and my HRV increased about 10%.
Conclusion
I didn’t track my energy levels or mood, but my subjective review is that my “top end” energy was about the same, with a more consistent, steady energy throughout the day. Those mid-day energy troughs were eliminated, which was a big win.
This is decidedly not evidence that cold showers are a sleep panacea. I’m always wary of n=1 experiments, but the results were uniformly positive, so this is something I’ll definitely continue.
As for the mechanism of action, my hunch is that there are equal parts placebo, and a stress-reducing, mood-enhancing effect, leading to better sleep.
I highly recommend people give this a shot for at least a few consecutive days. Once you get past the initial burn, you’ll settle into what soon becomes an unexpected endorphin high that lasts longer than you’d expect.
With this in the books, my next experiment will be not eating for at least 2 hours before bed. This is a commonly espoused sleep tactic, so we’ll see what the impact is. I’ve noticed that very large meals before bed increase my heart rate, so I’d expect that to come down, but I’m not sure how or if this will affect other metrics. Stay tuned.