How to Use Cold & Heat Exposure to Optimize Health

Soberg's landmark study: minimum cold and heat thresholds for boosting brown fat and metabolism

Dr. Susanna Soberg's seminal research at the University of Copenhagen established the minimum effective doses of deliberate cold and heat exposure.

"But if you are adapted, it kind of subsides with time with adaptation. So what you can do is that you can train this cold exposure and you can kind of like get adapted to it."

Soberg's research: first to define minimum sauna and cold doses for metabolic benefits

Soberg was the first to establish minimum thresholds for heat and cold exposure to activate brown fat thermogenesis and improve metabolic markers.

"She is the first author of a seminal study which discovered the minimum thresholds for deliberate heat and deliberate cold exposure for increasing brown fat thermogenesis, which is essentially a mode of increasing heat production and metabolism in the body, and for establishing actionable protocols that can be used outside of the laboratory to improve metabolism and human health."

The after-drop effect: core temperature keeps falling after you leave cold water

After exiting cold water, core temperature continues dropping as constricted blood vessels reopen and cold peripheral blood flows back to the core.

"Something called the after drop is when your core temperature decreases even after you get out of the cold water."

Cold-adapted Scandinavians in their 70s-80s look decades younger without hormones

Huberman observed remarkably fit people in their 70s and 80s in Copenhagen who are clearly not using hormone augmentation.

"And I know all the telltale signs of hormone augmentation. I'm very good at spotting that."

Copenhagen swimmers of all ages treat cold water like nothing -- fitness culture in action

In Copenhagen, people of all ages swim in cold water year-round as a normal part of life.

"But also when we did see swimmers, they were swimming in this cold water and like it was nothing. And the range and age of the swimmers was what was remarkable."

First-time cold exposure feels painful, but adaptation happens with consistent practice

Soberg describes her first cold water experience as painful, like the regret of running too far after a break.

"I read the literature. I understood in theory what happens when you go into cold water. But I completely understood it when I first tried it."

The diving response: cold water slows heart rate and oxygen consumption via the vagus nerve

Submerging in cold water triggers the mammalian diving response, which activates the vagus nerve, slows heart rate, and reduces oxygen consumption.

"And when you do that, you have an activation of your diving response and that's going to slow down the, you can say, the consumption of oxygen also in your body and that's going to slow down, you can say, the consumption of oxygen also in your body, and that's going to slow down your heart rate. Could I pause you on this?"

Protocol: 3 cold dips of 1-2 min + 2 sauna sessions at 80C, done 2-3 times per week

Study participants did 3 rounds of 1-2 minute cold dips alternating with 2 sauna sessions at about 80 degrees Celsius, visiting 2-3 times per week.

"They do this two to three times per week. And for each time they go, each day they go, they take three rounds of, so three dips and two sauna sessions."

Minimum effective dose: 11 minutes total cold per week across 2-3 sessions

Soberg's study found 11 minutes of total cold exposure per week, spread across 2-3 sessions, was the minimum threshold for metabolic benefits.

"This was ended up being 11 minutes in total per week. So not in one session, of course, but they had two to three visits to the water and the sauna per week."

Minimum effective dose: 57 minutes total sauna per week, about 10-15 min per session

The study found 57 minutes of total sauna time per week was the minimum threshold for metabolic benefits.

"For the sauna, my study showed 57 minutes in total per week. And if we also then divide it out on these two to three days and two sessions each day, correspond to 10 to 15 minutes."

Danish winter swimmers report feeling free -- the mental health dimension of cold exposure

People in Denmark do winter swimming primarily because it makes them feel free, not just for physical benefits.

"People in Denmark who do this, they do the winter swimming because they feel free when they do it."

Cold and heat exposure lower systemic inflammation, potentially preventing depression and Alzheimer's

The combination of cold and heat exposure lowers systemic inflammation, which may help prevent lifestyle diseases including type 2 diabetes.

"If you have your little skinny bikini on, it's not going to do any difference to your cold exposure or your adaptation. It's not going to do any difference for your benefits, of course."

Start with cold showers, then still water immersion -- open water carries drowning risk

Hypothermia is a serious risk, especially for smaller-bodied people and children.

"Hypothermia is no joke. The cold is a powerful stimulus and kids and smaller bodied people are at a greater risk of hypothermia."

Cold and heat as hormetic micro-stress: brief exposure triggers anti-inflammatory adaptation

Brief cold and heat exposures act as hormetic micro-stressors that lower whole-body inflammation.

"I think it's very important to think about the cold exposure and the heat exposure as something that then lowers the inflammation in the body."

Why people wear wool hats in saunas: it lets you stay in longer by insulating the head

In Scandinavian sauna tradition, wool hats insulate the head from direct heat, allowing longer and more beneficial sessions.

"The reason that people wear wool hats in the sauna is it actually lets you stay in the sauna longer because it takes a lot of heat to the skin before you feel that you have to get out."

Safety first: hypothermia risk is real, start conservatively and build up gradually

Hypothermia is a real danger, especially for children and smaller people.

"Hypothermia is no joke. So I'm really glad that this is coming up because the cold is a powerful stimulus and kids and smaller bodied people are at a greater risk of hypothermia."

Women may need different cold protocols, but brief micro-stress exposure works for both sexes

Brown fat activation should work the same in men and women, but tolerance for prolonged cold exposure differs.

"So I would say that women also regarding activation of the brown fit, it should be the same in theory, but I don't know if women actually do need to have another protocol when it comes to this rapid cold exposure."

Soberg's study is a landmark: first high-resolution data on cold/heat exposure thresholds

Huberman calls Soberg's research a landmark in the field, noting it provides the first detailed, modern data on minimum cold and heat exposure.

"Because frankly, there just haven't been that many high-resolution, detailed modern studies of this. There have been studies of sauna."

Soberg study is rare modern research: most prior cold studies used impractical temperatures

Most previous cold exposure research used extreme, impractical temperatures.

"There are a lot of groups in physiology that work on hypothermia and very cold exposure, but most of the temperatures used in those days just aren't practical. So first of all, I just want to thank you for doing the work that you've done and for the work that you continue to do."