Saunas can improve sleep quality by creating a high temperature gradient before bed, which accelerates sleep onset and maintenance.

“the one thing that I felt sana really mattered for was sleep and not for the growth hormone level but because I think there's pretty good data that a great way to sleep is to create a high gradient of temperature so the faster the more negative the derivative of temperature DT by DT when you sleep the faster you'll go to sleep in the longer you'll stay asleep”

“by heating you up right before bed if we're heating up your hands and your feet we're helping you actually open the vasculature and dump some heat it's going to create that gradient and we think that gradient might be important for people with the early kind of insomnia with falling asleep at the start of the night”

“What happens is that you get into the bath, you get massive vasodilation. All of the vessels open up on the surface of your skin. That draws, it almost charms, the blood out from the core of your body to the surface. And your skin and your hands and your feet especially act like these wonderful thermal radiators. And they dissipate the heat. So you get out of the bath, and your core body temperature actually plummets, and that's what you need for good sleep.”