Essentials: Cold & Heat Exposure for Metabolic Health | Dr. Susanna Søberg

Welcome to Huberman Lab Essentials. I’m Andrew Huberman, and today I’m joined by Dr. Susanna Søberg to talk about deliberate cold, heat, metabolism, and practical ways to use these stressors. Susanna, for someone starting out, how should cold exposure feel?

It should be uncomfortably cold—that is enough. Early on, you may breathe fast or gasp; that’s the cold shock and sympathetic activation. With practice, that response settles down, but cold water is not supposed to be cozy. If you’re loving every second of it, I’m thinking, something is wrong.

Does the method matter: a shower, neck-deep plunge, putting the head under, or simply walking outdoors in light clothing?

They are different doses. Water covers more skin and activates cold receptors faster, but cold air also raises norepinephrine and recruits brown fat, our heat-producing tissue. Brown fat responds first; muscles join in through shivering, and together they protect body temperature.

And shivering itself isn’t necessarily the problem. You clarified something I’d heard described but never understood well: after leaving cold water, vessels reopen, cooled blood returns inward, and core temperature can continue falling.

Yes, that after-drop is why you should not stay in long enough to become too hypothermic. But ordinary shivering can be viewed a bit like exercise: a hard, healthy stress. Cold and heat challenge cells, helping them become more robust for the next exposure.

You don’t need to begin with an ice bath. Even a cold hand, cold wind, or sleeping in a cooler room can stimulate brown fat. One study found that a month sleeping at nineteen degrees Celsius was associated with more brown-fat activity and improved insulin sensitivity; the face may be enough, since it has many cold receptors.

In my study, winter swimmers combined short outdoor dips with sauna two or three times weekly. They had better insulin sensitivity, used less insulin, and cleared glucose faster than matched controls. The cold total was about eleven minutes weekly, in one- to two-minute bouts; sauna was about fifty-seven minutes weekly. More is not automatically better—too much can exhaust the cells.

That’s encouraging: better glucose control with lower insulin release is precisely the direction people want. And the key seems less about a rigid temperature prescription than repeated transitions between warm and cold.

Exactly. End on cold if your goal is to make the body rewarm itself, keeping brown fat and muscles working afterward. But please vary it; you do not need ice every time. Even temperatures up to around twelve degrees Celsius in water, or cool air, can work. It’s the changing temperature that challenges the body.

Susanna, thank you for your research and for making this less extreme and more usable. Your work offers a remarkable direction for studying deliberate cold and heat exposure.