Chill Out. Sleep Deep: The connection between cold exposure and sleep

If you’ve ever cranked up the AC or kicked off the covers on a hot night, you already understand one of the fundamental truths of sleep: cooler temperatures promote better rest. Our core body temperature naturally drops in the evening as part of the circadian rhythm, signalling to the body that it’s time to sleep. This cooling process is essential for facilitating deep, restorative sleep.

For decades, the relationship between cold exposure and sleep has been largely anecdotal – science had little to say on the matter. That’s beginning to change.

Emerging research is now shedding light on how cold water immersion (CWI) may influence sleep quality. While studies on this specific link are still in their infancy, what we do know about sleep physiology suggests a compelling case for cold exposure as a potential sleep aid.

Deep Sleep vs. REM Sleep: why the distinction matters

To understand how cold exposure might enhance sleep, it helps to break down the two most well-known sleep stages:

• Slow-wave sleep (deep sleep): This is the most restorative phase of sleep, characterised by slow brain waves, reduced heart rate, and muscle relaxation. It’s crucial for physical recovery, immune function, and memory consolidation.
• REM (Rapid Eye Movement) sleep: This stage is where most dreaming occurs. The brain is highly active, and this phase is linked to cognitive function, emotional regulation, and learning. Unlike deep sleep, REM sleep does not benefit as much from cooler temperatures and may even be slightly suppressed by extreme cold exposure.

Why does this matter? Because if cold therapy enhances deep sleep – without significantly disrupting REM sleep – it could provide a net positive effect on overall sleep quality and recovery.

The Science: what the research says

One of the most compelling findings comes from a study conducted at the University of Poitiers in France, which examined the effects of whole-body cryo-stimulation (-90°C exposure) on young, active adults. Over five consecutive days, participants experienced a significant increase in slow-wave sleep, averaging 7.3 additional minutes during the first two sleep cycles. Beyond sleep improvements, mood enhancements and reduced anxiety were observed, with particularly strong effects in women.

Beyond cryotherapy, cold-water immersion (CWI) has also been investigated for its impact on sleep. A systematic review analysing data from 11 studies, encompassing 3,177 participants, found that CWI was associated with improved sleep quality and reduced stress levels, especially within the first 12 hours post-exposure. However, these benefits appeared to be short-lived, suggesting that regular and consistent exposure may be necessary to sustain long-term effects for quality sleep.

Similarly, a study published in Physiology & Behaviour examined the effects of regular CWI (10°C for 10 minutes, three times per week over four weeks) and found notable improvements in both sleep quality, with a clear decrease in the number of sleep disturbances.

Based on research by Knill Jones et al. (2024) we’d recommend cold therapy at least 3 times per week, for a minimum of 4-weeks to reduce sleep disturbances and improve overall sleep quality. We advise plunging at least 3–4 hours before bedtime to allow any post-immersion adrenaline to fully subside, setting the stage for deeper, more restful sleep. However, we do know a few cool cats who love plunging an hour before bed for the best results, but it’s personal and unique to everyone.

Why do so many people sleep better after an ice bath?

Ask any regular cold plunger, and you’ll often hear the same story: the best night’s sleep often follows a deep dive into cold water. While science is still catching up, one theory for this sleep upgrade lies in melatonin – the hormone that governs your sleep-wake cycle. Animal studies suggest that cold exposure can increase melatonin activity, enhancing the body's natural transition into deep sleep. It's not yet conclusive for humans, but given how consistently people report sleeping well post-plunge, it's a compelling area for future research – and a likely contributor to those knockout nights.

Our favourite tips for your sleep kit

Quality sleep is the result of a medley of factors: circadian rhythm regulation, light exposure, stress management, and physical activity, to name a few. With over 10 years of Oura data from some of our team members, we’ve found some patterns that are impossible to ignore. If you’re serious about levelling up your sleep (and amplifying the effects of cold therapy), these rules are game-changers:

• No food three hours before bed: This is our biggest one (we see it in our resting heart rate and heart rate variability).
• Blue-blocking glasses in the evening: protect melatonin production and help your brain shift into sleep mode.
• No alcohol: Sorry, not sorry. Even one drink can trash your REM and deep sleep, even if you think it helps you fall asleep.
• Consistent sleep + wake times: yes, even on weekends. Your circadian rhythm loves predictability.
• Morning sunlight: Exposure within the first hour of waking helps regulate your internal clock and boosts sleep hormone production later.
• Intentional wind-down routine: breathwork, stretching, or anything that calms your system pays serious dividends.

Integrating the cold into practice

By leveraging what we already know about temperature regulation and sleep physiology, combined with emerging research on cold therapy, we can begin to harness the cold as a strategic tool for deeper, more restorative sleep. The cold isn’t a cure-all, but in the right context, it just might help you sleep like a (very chilled-out) baby.