Huberman LabHow to Use Cold & Heat Exposure to Improve Your Health | Dr. Susanna Søberg
CHAPTERS
- 0:00 – 5:40
Introduction to Dr. Søberg and the Science of Cold and Heat
Huberman introduces Dr. Susanna Søberg, outlining her background in metabolism research and her seminal 2021 Cell Reports Medicine paper on cold and heat thresholds for brown fat activation. He previews the episode’s focus: practical, science-based protocols for deliberate cold and heat exposure and their impact on metabolism, hormones, and neurotransmitters.
- •Dr. Søberg’s PhD work centered on deliberate cold and heat exposure and human metabolism.
- •Her 2021 paper identified minimum thresholds of cold and heat to activate brown fat thermogenesis.
- •Discussion will cover catecholamines (dopamine, epinephrine, norepinephrine), hormones, safety, and protocols.
- •Her book ‘Winter Swimming’ breaks down practical aspects of cold and heat exposure for laypeople.
- 5:40 – 14:40
Sponsors and Live Tour Announcements
Huberman pauses for sponsor messages and to announce live Brain-Body Contract events. This segment is unrelated to the core scientific discussion but frames the podcast’s funding model and outreach activities.
- •Sponsors include Plunge (cold plunges), Maui Nui Venison, Thesis Nootropics, Athletic Greens, and InsideTracker.
- •Brief descriptions of product relevance to health and performance.
- •Huberman announces live lecture tours in Toronto and Chicago.
- •He reiterates the podcast’s mission to provide zero-cost, science-based tools.
- 14:40 – 23:20
What Happens During Cold Shock? Physiology and Psychology
Søberg explains what occurs when someone enters uncomfortably cold water—whether via open water, cold plunge, or shower. They detail the cold shock response, sympathetic activation, catecholamine release, breathing changes, and how adaptation blunts the shock over time.
- •Cold exposure activates the sympathetic nervous system and catecholamines (dopamine, norepinephrine, epinephrine).
- •Cold shock is defined by hyperventilation and gasping; this attenuates with adaptation.
- •The relevant intensity is relative to skin and core temperature, not just absolute water temperature.
- •Repeated exposure builds resilience and reduces the panic/shock phase.
- 23:20 – 33:20
Discomfort, Adaptation, and Individual Differences in Cold Tolerance
They discuss why some people seem to tolerate cold easily while others dread it, even among elite performers such as special operations soldiers. Søberg notes nervous system sensitivity, avoidance behavior, and cold pain perception, and emphasizes that adaptation reduces distress over time.
- •Psychological and nervous system sensitivity influences cold tolerance; phenotype doesn’t reliably predict response.
- •Avoiding cold tends to increase perceived cold pain over time.
- •Those habitually exposed to cold (e.g., outdoor workers, winter swimmers) appear more resilient.
- •Discomfort is expected and desirable as a hormetic stress, analogous to strenuous exercise.
- 33:20 – 41:40
Cold Showers vs. Full Immersion vs. Ambient Cold
The discussion compares different cold-exposure modalities: outdoor cold air, cold showers, partial immersion, and full-body submersion. Søberg explains how coverage of skin with cold water strongly affects receptor activation and brown fat stimulation, and why cold-shower research lags behind immersion studies.
- •Cold water immersion covers more skin with denser molecules than air, giving a more potent stimulus.
- •Outdoor cold in light clothing still activates sympathetic output and brown fat.
- •Cold showers almost certainly activate brown fat, but standardized human data are scarce due to methodological challenges.
- •Any exposure that feels uncomfortably cold at the skin will recruit brown fat activity.
- 41:40 – 50:20
How Cold Signals Reach and Activate Brown Fat
Søberg outlines the three main pathways linking skin-cold sensing to brown fat activation. She explains hypothalamic integration, direct skin-to-BAT innervation, and muscle-shiver signaling, highlighting evolutionary redundancy for thermoregulation.
- •Cold receptors in skin send signals to the hypothalamus, which increases sympathetic output to BAT.
- •There is also a direct neural pathway from skin receptors to brown fat.
- •Shivering muscles send signals (e.g., via metabolites like succinate) that further activate BAT.
- •Redundant parallel pathways underscore brown fat’s importance in survival and homeostasis.
- 50:20 – 1:00:00
Shivering, Afterdrop, and Why Shiver Is Beneficial
They delve into shivering thermogenesis and the ‘afterdrop’ phenomenon: why core temperature continues to fall after leaving cold water. Søberg argues shiver should not be feared—it’s a sign of metabolic training—and she explains how afterdrop arises from reperfusion of cold peripheral blood.
- •Shivering burns calories, trains muscles and brown fat, and improves insulin sensitivity.
- •Afterdrop occurs as vasoconstricted vessels reopen, cold peripheral blood returns to the core, and core temperature dips further.
- •Shiver is the body’s response to afterdrop, ramping thermogenesis to restore core temperature.
- •Avoiding any shivering eliminates a meaningful part of the adaptive training stimulus.
- 1:00:00 – 1:09:10
Hormetic Stress: Why Cold and Heat Are Like Exercise
Huberman and Søberg parallel cold/heat stress with exercise-stress, emphasizing that transient, high-strain states (inflammation, high blood pressure, etc.) are necessary to produce long-term healthful adaptations. They also introduce the concept of cellular hormesis via heat-shock and cold-shock proteins.
- •During exercise, physiological markers (inflammation, blood pressure) look ‘unhealthy’ but drive healthier baselines afterward.
- •Cold and heat similarly induce transient stress that upregulates protective proteins and adaptive pathways.
- •Homeostatic stress in cells helps maintain robustness and resilience to future challenges.
- •Overdoing exposure flips hormesis into damaging chronic stress; dose and timing matter.
- 1:09:10 – 1:18:20
Long-Term Adaptations: Insulin Sensitivity, Blood Pressure, and Season-Long Change
Søberg reviews prior winter-swimming cohort data showing that a full winter season improves metabolic and cardiovascular markers. They relate this to her own controlled study and the broader concept of using cold for prevention of lifestyle diseases.
- •Season-long winter swimming (4–5 months) in middle-aged adults lowered blood pressure and resting heart rate.
- •Participants showed improved insulin sensitivity and glucose control after a season of cold exposure.
- •Such changes suggest preventive potential against type 2 diabetes and cardiovascular disease.
- •Søberg’s study aimed to connect these outcomes mechanistically to brown fat activation.
- 1:18:20 – 1:30:00
Deep Dive Into Brown Fat: Biology, Location, and Plasticity
They explore what brown fat is, where it resides, and how it changes with age, obesity, and chronic catecholamine exposure. Søberg highlights PET imaging data, cancer case evidence for BAT plasticity, and age-related loss linked to obesity.
- •Brown fat is located mainly in supraclavicular regions, along the spine, and around large vessels; it can appear in multiple depots.
- •BAT is rich in mitochondria and uniquely capable of non-shivering thermogenesis.
- •Case studies (pheochromocytoma) show that chronic high norepinephrine can dramatically expand BAT mass, which normalizes when the tumor is removed.
- •BAT volume/activity tends to decrease after age 40 and is inversely associated with obesity, though causality is unclear.
- 1:30:00 – 1:41:40
Environmental and Lifestyle Drivers of Brown Fat: Cold Rooms, Outdoor Work, and NEAT
Søberg discusses studies where mild chronic cold exposure—like sleeping at 19°C—grew brown fat and improved insulin sensitivity in just one month. Huberman adds anecdotal and classic physiology data on non-exercise activity and cold labs, reinforcing the role of daily environment.
- •Sleeping at 19°C with normal bedding for one month increased BAT volume and insulin sensitivity; warmer rooms reversed this.
- •Even localized cold (e.g., hand in 4°C water) can measurably activate BAT.
- •Outdoor workers and people chronically exposed to cold tend to retain more brown fat into older age.
- •Non-exercise activity thermogenesis (NEAT)—e.g., fidgeting, moving frequently—can add up to ~1,800 kcal/day in energy expenditure.
- 1:41:40 – 1:50:00
Scandinavian Culture: Seasonal Acclimation, Babies Sleeping Outside, and Winter Swimming
They explore traditional Nordic practices that incidentally train thermoregulation: underdressing before winter, overdressing before summer, and putting babies to nap outdoors. Observations from Copenhagen highlight widespread, age-spanning use of cold water.
- •Scandinavian wisdom: wear fewer layers in autumn to acclimate to winter cold, more layers in spring to handle summer heat.
- •Since mid-20th century, Danes have routinely let babies sleep outside in cold weather to build immune resilience.
- •These practices likely help maintain BAT activity and thermal robustness from early life.
- •Urban observation: many Danes of all ages comfortably swim in cold harbor water, reflecting cultural normalization of cold exposure.
- 1:50:00 – 2:00:00
Designing the Søberg Winter Swimmer Study
Søberg explains how she designed her human BAT study: observational rather than interventional, with experienced winter swimmers and matched controls. She describes recruitment, matching criteria, and why she initially used only male participants.
- •Study used experienced winter swimmers (2–3 previous seasons) versus matched non-swimming controls.
- •Groups were matched for BMI, diet (including vegetarian status), age, and general health.
- •Only men were included to avoid confounds from sex differences in brown fat and temperature perception.
- •Human metabolic trials are logistically complex and expensive, so the study was powered as a controlled proof of concept.
- 2:00:00 – 2:08:20
The Winter Swimming plus Sauna Protocol: Frequencies, Durations, Temperatures
She details the actual protocol winter swimmers were habitually using: frequency of visits, cold-immersion duration, sauna duration, and the order of exposure. This real-world pattern became the basis for deriving weekly ‘minimum effective dose’ thresholds.
- •Participants winter-swimming 2–3 times per week.
- •Each visit: three cold dips of 1–2 minutes in 2–12°C water, interspersed with two sauna bouts of 10–15 minutes at ~80°C.
- •Swimmers always ended on a cold dip, not on heat.
- •Weekly totals: ~11 minutes cold and ~57 minutes sauna, which are the key thresholds Søberg now cites.
- 2:08:20 – 2:16:40
Key Outcomes: Brown Fat Activation, Insulin Sensitivity, and Glucose Handling
Using PET/MRI scans, thermography, and metabolic testing, Søberg found winter swimmers had more active brown fat, used less insulin to control blood sugar, and cleared glucose from the bloodstream faster than controls, even when fasting and at rest.
- •Winter swimmers showed greater BAT activation both in cold and thermoneutral conditions.
- •They had lower fasting insulin levels and needed less insulin during glucose tolerance testing.
- •Their post-glucose blood-sugar curves dropped faster than in controls, demonstrating superior insulin sensitivity.
- •These differences were present regardless of body weight, suggesting direct BAT and thermoregulation effects.
- 2:16:40 – 2:23:20
Thermal Comfort Differences, Sex Differences, and Why Only Men Were Studied
They touch on known thermal and BAT differences between men and women, explaining why the initial study focused on men. Huberman and Søberg discuss comfort temperatures and surface temperature differences across sexes.
- •Women generally have more brown fat but colder hands, feet, and peripheral skin than men.
- •Men are thermally comfortable around 22°C; women around 24°C, per controlled studies.
- •Men have larger hearts and can pump more blood to periphery, contributing to warmer extremities.
- •Including both sexes would have required a much larger, more complex design, so the first study focused on one sex to reduce noise.
- 2:23:20 – 2:31:40
Diving Reflex, Face Dunking, and Head-Under Considerations
They discuss the mammalian diving reflex and whether immersing the head or face changes the physiological profile of cold exposure. Søberg cautions about additional heat loss and potential dizziness when submerging the head.
- •Submerging the body in cold water activates the diving response, reducing oxygen consumption and slowing heart rate over time.
- •Face immersion may add parasympathetic input and serotonin effects, but evidence is limited.
- •Studies show full-body submersion up to the neck in 0°C water reduces cerebral blood flow by 30–40%; dunking the head further increases core heat loss (~36% more).
- •Keeping the head above water or wearing a beanie in open, windy environments can reduce brain-freeze effects and hypothermia risk.
- 2:31:40 – 2:40:00
Why End on Cold: The Søberg Principle
Søberg articulates the logic behind her recommendation to finish sessions with cold: doing so forces your body to self-reheat, keeping brown fat and muscles working for hours afterward and extending hormonal and metabolic benefits.
- •Ending on heat (e.g., hot shower or sauna) reduces the need for endogenous thermogenesis post-session.
- •Ending on cold intensifies afterdrop and demands sustained BAT and muscle activation to restore core temperature.
- •This extended thermogenic period raises energy expenditure and prolongs elevated catecholamine levels.
- •Practically, it means cold → heat → cold, dress warmly, move around, and let your body warm itself.
- 2:40:00 – 2:50:00
Practical Adaptation: Frequency, Bout Structure, and Temperature Variation
They translate the research into pragmatic advice: how to reach ~11 minutes/week of cold and ~57 minutes/week of heat, why multiple short bouts are superior to one long one, and why varying temperatures keeps the system adaptive.
- •Aim for around 11 total minutes of uncomfortably cold water per week and 57 minutes of sauna per week as a starting threshold.
- •Divide this into 2–4 sessions rather than one long exposure to repeatedly trigger the shock-adaptation cycle.
- •Varying temperatures (seasonally, by changing settings, or via different times of day) prevents over-adaptation and preserves hormesis.
- •Those who dread the cold often gain the most, as their sympathetic response and subsequent adaptation are largest.
- 2:50:00 – 3:00:00
Safety and Special Populations: Kids, Small Bodies, Raynaud’s, and Extremity Pain
The conversation turns to safety: hypothermia risk in children and smaller adults, strategies for managing hand/foot pain, and the lack of rigorous studies on conditions like Raynaud’s and autoimmune disease in relation to cold exposure.
- •Children and smaller-bodied people lose heat faster and can defend core temperature during ≈1 minute immersions but become hypothermic sooner with longer exposures.
- •Protocols for kids should be very conservative, supervised, and typically begin with mild cold showers or brief dips.
- •People with painful hands/feet can keep hands out of the water or wear neoprene booties without sacrificing core benefits.
- •Anecdotal reports suggest possible improvement in Raynaud’s with graded exposure, but robust controlled data are lacking.
- 3:00:00 – 3:06:40
Social Norms, Skinny Dipping, and Scandinavian Sauna Culture
They briefly discuss clothing-optional winter swimming and sauna traditions in Denmark, clarifying that nudity offers no physiological advantage—only psychological and cultural dimensions. Huberman notes similar practices in Russian banyas.
- •Some older Danish winter-swimming clubs are traditionally nude; newer clubs tend to require swimwear.
- •Skinny dipping does not materially change cold exposure or adaptation relative to minimal swimwear.
- •Cultural contexts influence comfort and norms around nudity but not core thermogenic physiology.
- •Phones and cameras are gradually eroding some nude traditions due to privacy concerns.
- 3:06:40 – 3:15:00
Outlier Case: A Winter Swimmer With No Measurable Brown Fat
Søberg recounts one remarkable subject: an experienced winter swimmer who had no detectable brown fat on PET/MRI. His responses during cooling experiments resembled controls, and he shivered more vigorously and earlier than other swimmers.
- •One male winter swimmer exhibited no PET-detectable BAT despite regular cold exposure.
- •He shivered more and at higher intensities and had temperature regulation patterns closer to non-swimming controls.
- •His insulin and glucose responses were also more like controls, suggesting BAT absence or dysfunction.
- •He was treated as an outlier/‘knockout’ in analysis, reinforcing the role of BAT in the measured benefits.
- 3:15:00 – 3:25:00
Inflammation, Mental Health, and Future Research Directions
Søberg discusses inflammatory markers (IL-6, IL-10) and their potential link to reduced chronic inflammation and mental health benefits. She highlights gaps: sleep, mood, autoimmune conditions, and a forthcoming study including both men and women.
- •Cold and heat exposure acutely increase IL-6 and anti-inflammatory IL-10, likely reducing chronic inflammatory tone over time.
- •Lower blood pressure and improved insulin sensitivity suggest systemic anti-inflammatory effects.
- •Chronic inflammation contributes to depression, anxiety, Alzheimer’s, and metabolic disease, making temperature hormesis a potentially valuable preventive tool.
- •Søberg has completed a new, not-yet-published study that includes both men and women to explore sex-specific responses.
- 3:25:00
Closing Reflections and Resources
Huberman thanks Søberg and underscores the importance of rigorous yet accessible work on cold and heat exposure. He directs listeners to her book and institute, mentions the Huberman Lab newsletter and social channels, and reiterates the role of science-based tools in everyday life.
- •Søberg’s work is among the first to tightly link real-world cold/heat practices to quantified BAT and metabolic changes.
- •Her book ‘Winter Swimming’ and The Søberg Institute provide further protocols and education.
- •Huberman encourages experimentation within safety bounds and emphasizes that discomfort is the signal, not the goal of extremity.
- •Podcast support options (sponsors, newsletter, social media) are summarized for listeners.
