Sleep and Body Temperature: How Heat and Cold Affect Sleep Quality

Why is it important to sleep well?

Let’s say you eat well, exercise regularly, and even incorporate sauna and cold exposure sessions into your routine. None of that really works if you don’t sleep well (both in terms of quantity and quality). This is, basically, what Peter Attia tells us.

Dr. Attia considers sleep to be the foundation of health. Why? Because during sleep, the body carries out vital physiological repair processes: brain clearance, cellular repair, memory consolidation, cardiovascular recovery, immune system support, etc.

To understand just how fundamental sleep is, let’s look at this study: Impaired insulin signaling in human adipocytes after experimental sleep restriction: a randomized, crossover study.

Researchers took 7 young, healthy adults and divided them into 2 groups. For 4 days, one group slept 8.5 hours and the other 4.5 hours per night.
At the end of each period, samples of their fat tissue were analyzed to see what was happening with their insulin.

What did they find? After just 4 days of restricted sleep, the fat cells showed lower insulin sensitivity. These results suggest that not getting enough sleep can have a direct negative impact on metabolism and lead to a state of insulin resistance, even in young and healthy people.

Now that we understand how important sleep is, let’s talk about sleep itself. One of the key pieces when it comes to sleep is body temperature.

Circadian Rhythm and Body Temperature

We all have a circadian rhythm: an internal biological clock that helps regulate when we wake up, when we sleep, and other processes in the body.

And you may not know this, but our body temperature also has a “rhythm,” following a 24-hour cycle that works more or less like this:

Between 4 and 6 AM, core body temperature reaches its lowest point, which coincides with the deepest resting phase.
Between 6 and 8 AM, body temperature starts to gradually rise. The body reduces melatonin and increases cortisol to help us wake up.
During the day, temperature rises a little more and then remains relatively stable.
Between 4 and 6 PM, we reach our highest body temperature of the day (around 37 °C).
From around 6–7 PM, body temperature begins to drop and melatonin production increases to promote sleep.
From 11 PM to 2 AM, body temperature drops rapidly, facilitating deep sleep.

In short: body temperature rises to activate us and falls to help us rest.

Sleep and Temperature

As we’ve seen, body temperature and sleep are closely connected. In order to fall asleep, your body needs to dissipate heat and lower its core temperature.

The drop in body temperature is one of the signals the brain uses to understand that the day is over (remember the circadian rhythm?) and that it’s time to rest. Based on this signal (among others), the brain increases the production of melatonin, the hormone that makes you feel sleepy and helps you fall asleep.

In this sense, modifying the external temperature is one of the tools we have at hand to improve sleep.

If the temperature in your bedroom is too high, it can interfere with the body’s natural cooling process, leading to fragmented sleep and nighttime awakenings. On the other hand, a cooler room supports the body’s natural thermoregulation, making it easier to fall asleep and stay asleep.

So, how cool should your bedroom be? In general, 18–20 °C is recommended. But this is subjective, since everyone has their own internal thermostat. So, basically, your room should feel cool to you. Not cold. Cool.

4 Habits to Sleep Better

Here are some other tips that can help you fall asleep more easily and sleep better:

Sauna or hot-water immersion. You can “hack” this natural mechanism through heat exposure. Around two hours before going to bed, do a sauna session or take a hot bath. This raises your body temperature. Once the session is over, your body gets to work bringing your temperature back to normal and, as a result, lowering it.
Screens OFF. Yes, you’ve read it a million times already. But the blue light from screens really can be your worst enemy. Screen light can interfere with the signals our biological clock receives, keeping the brain in a more active state.
Caffeine. Avoid coffee, tea or anything with caffeine from around 5–6 PM onwards.
In the morning: when you wake up, expose yourself to natural morning light. This is one of the strongest signals for your brain to understand that it’s time to activate. In this way, you’re helping synchronize your biological clock, which at night will help your body and brain “wind down.”

Conclusion

Getting good sleep is essential. And body temperature is one of the key pieces of the puzzle. Our body needs to lose heat to initiate sleep and, throughout the night, continues adjusting its temperature as part of our circadian rhythm.

The good news is that you can support this process with simple habits: getting natural light in the morning, keeping your bedroom cool, limiting caffeine and screens at night and, if you enjoy it, incorporating a sauna session or hot bath a few hours before bed.

It’s not about finding the perfect hack or obsessing over the numbers. It’s about understanding how our body works and working with it so we can live life to the fullest.