Why does a cool bedroom help you sleep?

On Huberman Lab (October 2021), Stanford biologist Craig Heller, who studies how the body controls its temperature, was asked by host Andrew Huberman what people should know about sleep that they rarely hear. Near the end of that conversation, he explained why a cool bedroom works. His reason isn't the one most of us assume.

It's better to have a cool environment because it's easier to thermoregulate.

Craig Heller, Huberman Lab, 2021

Your thermostat turns down at night

Heller starts with the body clock. As bedtime approaches, your clock lowers your internal thermostat, so your body aims for a slightly lower core temperature through the night. That's why you can feel a little chilly when you get into bed. So you pile on the blankets, and a few hours later you wake up hot and throw them off. Your thermostat has moved, and your bedding hasn't.

A cool room gives you an easy way to shed that heat without waking. Heat leaves the body mainly through the palms, the soles of the feet and the face. In a cool room, sliding a hand or a foot out from under the covers is enough, and you can do it half asleep. In a warm room, those surfaces have nowhere to send the heat, so you're more likely to wake up and fight with the covers.

Huberman asked about socks, which he assumed were bad advice. Heller didn't dismiss them. Toes are among the body's most cold-sensitive spots, so socks can keep you comfortable if cold feet bother you. If you're already warm, you won't want them.

What the research adds

The same logic explains a tip that sounds like its opposite: a warm shower or bath before bed. Warm water draws blood to your hands and feet, and when you step out, heat pours off them. A 2019 review that pooled 13 studies found that a shower or bath at 40 to 42.5 °C (104 to 108.5 °F), taken one to two hours before bed, helped people fall asleep sooner, even when it lasted as little as 10 minutes. The authors add that the research is still limited, especially on the best timing and length.

"Cool" isn't a single number. One study that followed older adults at home found they slept best when the bedroom was between 20 and 25 °C (68 and 77 °F), with sleep getting worse above and below that range. It was an observational study, so it shows a link, not a target. Comfort is the better test: cool enough that you want a blanket, never so cold that you lie there tense.

How this fits the Better Sleep program

In the 1h Protocol for Better Sleep, the chapter "Tonight, hour by hour" sets your evening to your own times. Part of it is the runway before lights-out, which starts with a warm shower and a bedroom cool enough that you want a blanket, dark and quiet; Heller's point about hands, feet and a cool room sits right there as an expert note. Later, "Tonight, again" helps you set up the first changes at home, and your fourteen-night sheet shows whether they make a difference for you. The first chapter is free, so you can find your sleep pattern before deciding anything else.

Source: Huberman Lab, Dr. Craig Heller: Using Temperature for Performance, Brain & Body Health, 4 Oct 2021 Research: Haghayegh et al., warm shower or bath before bed, meta-analysis (2019) · Baniassadi et al., bedroom temperature and sleep in older adults (2023)