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May 15, 2023 • 2hr 26min
Dr. Susanna Søberg: How to Use Cold & Heat Exposure to Improve Your Health
Huberman Lab
In this episode, Dr. Andrew Huberman interviews Dr. Susanna Søberg, a researcher who studies the effects of deliberate cold and heat exposure on human physiology and metabolism. Dr. Søberg conducted a landmark study published in Cell Reports Medicine examining how winter swimming impacts brown fat activation, insulin sensitivity, and other metabolic markers. The discussion covers the science behind cold and heat exposure, practical protocols for implementing these practices, and their potential health benefits.
Dr. Susanna Søberg: How to Use Cold & Heat Exposure to Improve Your Health
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Key Takeaways
- Cold exposure activates brown fat, which increases metabolism and improves insulin sensitivity
- The minimum effective dose for cold exposure benefits is about 11 minutes total per week, divided into 2-3 sessions of 1-2 minutes each
- Ending cold exposure sessions with cold (rather than warming up) prolongs the metabolic benefits
- Alternating between cold and heat exposure provides additional benefits by challenging the body to adapt
- Cold exposure triggers release of norepinephrine, which activates brown fat and increases alertness/focus
- Women tend to have more brown fat than men and may respond differently to cold exposure
- Brief, frequent cold exposures are more beneficial than longer, less frequent exposures
- Cold exposure can reduce inflammation and may help with conditions like depression and anxiety
- Children and smaller adults need to be more cautious with cold exposure due to higher risk of hypothermia
Introduction
In this episode, Dr. Andrew Huberman interviews Dr. Susanna Søberg, a researcher who studies the effects of deliberate cold and heat exposure on human physiology and metabolism. Dr. Søberg conducted a landmark study published in Cell Reports Medicine examining how winter swimming impacts brown fat activation, insulin sensitivity, and other metabolic markers. The discussion covers the science behind cold and heat exposure, practical protocols for implementing these practices, and their potential health benefits.
Topics Discussed
Physiological Effects of Cold Exposure (7:40)
Dr. Søberg explains what happens in the body when exposed to uncomfortably cold temperatures:
- Activates the sympathetic nervous system
- Triggers release of catecholamines (norepinephrine, epinephrine, dopamine)
- Causes vasoconstriction to conserve core body heat
- Activates brown fat to generate heat
- Can induce shivering to produce heat through muscle contractions
The intensity of the response depends on the temperature difference between the body and environment. A larger difference produces a stronger "cold shock" response.
Cold Showers vs. Cold Immersion (17:37)
While there are fewer studies on cold showers compared to cold water immersion, Dr. Søberg notes that any form of cold exposure to the skin can activate brown fat. Cold immersion likely produces a stronger response since more of the body is exposed to cold. Key points:
- Cold showers still activate brown fat and provide benefits
- Cold immersion may be more potent due to greater skin surface exposure
- More research is needed to directly compare the effects
Brown Fat Activation and Function (22:11)
Dr. Søberg provides details on brown fat and its role in cold adaptation:
- Brown fat is rich in mitochondria and generates heat when activated
- It's located primarily around the collar bones, neck, and upper back in adults
- Cold exposure activates brown fat via:
- Direct pathway from skin cold receptors
- Hypothalamic activation
- Norepinephrine release
- Repeated cold exposure can increase brown fat volume and activity
- Women tend to have more brown fat than men
Shivering and the "After Drop" (25:22)
Dr. Søberg explains the phenomenon of shivering and the "after drop" in body temperature:
- Shivering generates heat through muscle contractions
- It often occurs after exiting cold water as blood flow returns to the skin
- The "after drop" is when core body temperature continues to fall after cold exposure
- Shivering helps activate brown fat and increase metabolism
"Shivering is just like when you go exercising in the training center and get that feeling of like, oh, this is tough now it hurts a little bit. Yeah, it's going to hurt because that's what shivering also does. But it's just a different way of training your cells in your body." - Dr. Susanna Søberg
Long-Term Health Benefits of Cold Exposure (31:08)
Dr. Søberg discusses some of the potential long-term health benefits of regular cold exposure:
- Improved insulin sensitivity and glucose regulation
- Lower blood pressure
- Reduced inflammation
- Increased brown fat volume and activity
- Enhanced ability to thermoregulate in cold environments
- Potential mood and cognitive benefits
Minimum Effective Dose for Cold Exposure (1:31:14)
Based on her research, Dr. Søberg provides guidelines for the minimum effective dose of cold exposure to see benefits:
- 11 minutes total per week of cold water immersion
- Divided into 2-3 sessions of 1-2 minutes each
- Water temperature around 2-15°C (35.6-59°F)
- Can be combined with sauna use (10-15 min sessions) for additional benefits
She emphasizes that longer exposures are not necessarily better and may be counterproductive.
The "Søberg Principle": Ending on Cold (1:55:40)
Dr. Søberg explains why it's beneficial to end cold exposure sessions with cold rather than warming up immediately:
- Prolongs activation of brown fat and metabolism
- Forces the body to generate its own heat
- Increases mitochondrial efficiency in brown fat and muscle cells
- May improve sleep by facilitating natural body temperature drop at night
"If you end on the cold, you have an exercise for your body going on for hours afterwards. That's not only on your metabolism, but it's also going to keep your neurotransmitters activated as well." - Dr. Susanna Søberg
Cold Exposure Timing and Frequency (2:19:57)
Dr. Søberg discusses optimal timing and frequency for cold exposure:
- Varying exposure times throughout the day may be beneficial due to natural circadian temperature fluctuations
- Brief, frequent exposures are likely more effective than longer, less frequent sessions
- Alternating between cold and heat exposure provides additional benefits
- Consistency is more important than precise timing
Safety Considerations (2:11:29)
Important safety considerations for cold exposure practices:
- Children and smaller adults are at higher risk of hypothermia - limit exposure time
- Submerging the head increases heat loss by 36% - use caution
- People with Raynaud's syndrome should be cautious and may need to keep hands/feet out of water
- Always practice cold exposure safely and with supervision when starting out
Conclusion
Dr. Søberg's research provides compelling evidence for the metabolic and health benefits of brief, consistent cold exposure practices. By activating brown fat, cold exposure can improve insulin sensitivity, reduce inflammation, and enhance overall metabolic health. The key is to start gradually, be consistent, and focus on brief exposures rather than prolonged sessions. Combining cold exposure with heat exposure (e.g. sauna use) may provide additional benefits by challenging the body to adapt to temperature changes. While more research is needed, especially regarding differences between men and women, cold exposure appears to be a powerful tool for improving health when implemented safely and consistently.
