Dr. Susanna Søberg, Ph.D. (@SusannaSberg1) is the founder of “Soeberg Institute” and “The Thermalist cure”. Susanna is a leading international scientist and expert in cold and heat therapy to reduce stress and improve health, and sleep and optimize performance. Her research focuses on the effects of deliberate cold and deliberate heat exposure on metabolism and other aspects of human physiology.    
Andrew Huberman and Susanna Søberg discuss how deliberate heat and cold can improve metabolism, cardiovascular and brain health, balance hormones, and decrease inflammation. Dr. Søberg reviews how to leverage specific protocols depending on goals, how to apply various types of heat and cold exposure and other actionable tools.
Host: Andrew Huberman (@hubermanlab)
If you are hot before entering cold, you will have an easier time than if you were cold beforehand
It’s difficult to put a precise temperature on “cold” because it is really more dependent on the difference between the current temperature of your skin and the temperature of the water
Tip: instead of a specific temperature, focus on uncomfortably cold (but safe)
You can train and adapt to cold exposure so shock subsides but it should be hard
People vary tremendously in ability to embrace the cold – the more you resist it, the worse it’ll feel for you
The more you cover your body in cold water, the more potent activation of cold receptors on the skin
Even being outside in cold air will increase norepinephrine and activate brown fat which increases metabolism
We know that as soon as our skin is cold, brown fat is activated – but we don’t have all the nuances of shower vs cold air, etc. for metabolism
Two tissues increase thermogenesis: brown fat and muscles (shivering)
Dive reflex: survival system which slows down oxygen response in the body, activation of the sympathetic nervous system after 1-2 minutes
Shivering increases metabolism in the body
After drop: sometimes shivering occurs once you’re already out of the cold
  • When you get in the cold, your blood vessels will constrict because you want to keep vital organs warm but they’ll open again once you’re out
Shivering is an autonomic response but shouldn’t be avoided – like exercise, shivering is training your cells to healthy stressors
Perception of cold doesn’t always correlate to shivering
As soon as you go into cold there’s an activation of brown fat
Every time you are exposed to cold, you’ll build adaptation – you’ll have more brown fat activated and will heat up faster because your body gets more efficient
Stress response will subside with consistent exposure so catecholamines will increase less
Insulin sensitivity will improve and metabolism will increase as a result
Other benefits: lower blood pressure, improved heart rate, better glucose balance
Brown fat: fat located around the organs
Brown fat is more widespread throughout the body than originally thought
Pathway from cold receptors to brown fat: cold receptors send a signal to the hypothalamus which increases noradrenaline which activates brown fat
  • Interestingly, brown fat is also activated when we get warmth on our skin
Brown fat is essential to our survival and evolution because temperature regulation is critical
Brown fat is elastic, it can grow and increase if there’s an increase in noradrenaline (but we want this within certain confines)
After age 40 people have less brown fat and obesity increases; the linearity of the relationship isn’t clear but both things exist
  • If you moved a lot in your early years and throughout life, you will keep more of your brown fat later in life
Ways to ease into cold exposure for brown fat activation and insulin sensitivity: sleeping in a very cold room (32F), dipping a hand in cold water, exposure to cold air
  • Some Scandinavian countries have infants and children sleep outside in the cold in the winter to cold adapt
Women have more brown fat than men and physiologically run colder than men
Was interested in potent cold exposure as proof of concept study
Participants: started as an observational study on male winter swimmers who swam 2-3 seasons
Method: participants stayed in cold water up to the neck for 1-2 minutes x 2-3 per week
  • Cold-heat cycling: participants start in a cold, go to a sauna (176F 10-15 minutes), and end in cold
Regular PET scans were taken to monitor brown fat
Monitoring of comfortability in cold was conducted
Results: winter swimmers produced less insulin and faster glucose clearance on all experimental days
Conclusion: cold exposure 11 minutes per week, spread out + 10-15 minutes per session (up to 30 minutes per week)
  • Inflammation biomarkers improved which can have a huge impact on disease
Interestingly, one participant didn’t have any brown fat
Regrettably, measurements of sleep were not assessed but anecdotally sleep seemed to improve  
Note, it doesn’t matter whether you are wearing a bathing suit or nude during cold exposure
End on cold: you want to end on cold to force your body to keep brown fat and muscles activated to heat the body up on its own
Ending on cold keeps neurotransmitters and thermogenesis going for hours after exposure
With practice, you will warm up faster
Tips for staying in the cold when it feels unbearable:
  • Keep hands out if it’s unbearable and/or wear boots or water shoes for feet
  • You can wear a cap and leave your head above the water
Cold exposure can’t be translated directly to children because they are smaller in mass
  • In one study, boys could tolerate for about 1 minute but could become hypothermic beyond
It’s possible protocols may be different for men and women but more studies are needed
It’s possible there are therapeutic benefits for those with autoimmune conditions but more studies need to be done – it is enough to be submerged up to the neck
Time of day and fasting state is unlikely to have an effect on cold exposure outcomes
Dr. Jack Kruse had a lot of thoughts about this episode – check out his critique here
Altered brown fat thermoregulation and enhanced cold-induced thermogenesis in young, healthy, winter-swimming men (Cell Reports Medicine)
Human physiological responses to immersion into water of different temperatures (European Journal of Applied Physiology)
Variations in leptin and insulin levels within one swimming season in non-obese female cold water swimmers (Scandinavian Journal of Clinical and Laboratory Investigation)
Mapping of human brown adipose tissue in lean and obese young men (Proceedings of the National Academy of Sciences)
A role for brown adipose tissue in diet-induced thermogenesis (Nature)
Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events (JAMA Internal Medicine)
Impact of cold exposure on life satisfaction and physical composition of soldiers (BMJ Military Health)
Thermal effects of whole head submersion in cold water on nonshivering humans (Journal of Applied Physiology)
Thermoregulation during rest and exercise in the cold in pre- and early pubescent boys and in young men (Journal of Applied Physiology)