How to Use Cold & Heat Exposure to Improve Your Health | Dr. Susanna Søberg

Episode Summary

Executive Summary: Andrew Huberman and Dr. Susanna Søberg discuss how deliberate cold and heat exposure affect metabolism, brown fat, catecholamines, insulin sensitivity, blood pressure, and stress adaptation. Søberg explains her research on winter swimming and sauna, emphasizing that brief, repeated exposures—not extreme duration—produce hormetic benefits, and that ending on cold may prolong metabolic activation.

Main Topics: Physiology of cold shock and sympathetic activation (Priority: 5/5): Cold exposure triggers cold receptors, the hypothalamus, sympathetic activation, catecholamine release, hyperventilation, and shivering; these responses are framed as adaptive stress rather than merely discomfort. Brown fat biology and thermogenesis (Priority: 5/5): Brown fat is presented as a metabolically active, plastic tissue that responds rapidly to cold and heat, helps regulate body temperature, and can expand or become more active with repeated exposure. Dose, protocol, and adaptation (Priority: 5/5): The discussion centers on how much cold/heat is needed for benefit, with Søberg arguing that short, repeated bouts are preferable to long exposures and that the stimulus should remain challenging. Sauna and combined heat-cold exposure (Priority: 4/5): Sauna is discussed as another hormetic stressor that can improve cardiovascular and metabolic health, with the combination of sauna and cold immersion used in Søberg’s study and in Scandinavian practice. Human study design and findings (Priority: 5/5): Søberg describes her winter-swimming study, including PET imaging, blood measures, shivering assessment, and temperature monitoring, showing improved insulin sensitivity, lower insulin, and greater brown fat activity in winter swimmers. Safety, individual differences, and practical guidance (Priority: 4/5): The conversation covers differences by sex, age, body size, cold sensitivity, Raynaud’s, head immersion, and the importance of avoiding hypothermia while still allowing enough discomfort to drive adaptation. Cultural and lifestyle context (Priority: 3/5): Scandinavian habits such as outdoor infant sleeping, winter swimming, and seasonal clothing choices are used to illustrate how regular temperature exposure may support resilience and health.

Key Arguments: Cold exposure should feel meaningfully uncomfortable; the goal is a cold-shock response, not comfort. Repeated brief exposures create adaptation in brown fat, muscles, and blood vessels, improving thermoregulation over time. Brown fat is a key first responder to cold and can be activated by cold skin exposure, cold water, and even mild cooling. Sauna and cold exposure both act as hormetic stressors that can improve cardiovascular and metabolic health when used in moderation. Ending on cold may extend post-exposure thermogenesis because the body must rewarm itself, keeping brown fat and muscles active. Winter swimmers in Søberg’s study showed better insulin sensitivity, lower insulin, and faster glucose clearance than controls. Cold adaptation may reduce the subjective stress response over time, but the stimulus should remain sufficient to provoke adaptation. People with smaller body size, children, or those with Raynaud’s may need extra caution because they lose heat faster and can become hypothermic sooner.

Data Points: Cold exposure threshold: 11 minutes per week total - Søberg’s study-derived minimum effective cold exposure, divided across sessions Sauna threshold: 57 minutes per week total - Study-derived heat exposure associated with benefits Cold session duration: 1-2 minutes - Typical winter-swimming/cold immersion bout in the study Sauna session duration: 10-15 minutes - Typical sauna bout in the study Sauna cardiovascular benefit threshold: ~19 minutes per session - Referenced Finnish observational data showing dose-response up to this point Upper sauna duration with no added benefit: ~30 minutes per session - Beyond this, additional cardiovascular benefit was not observed in the cited cohort Water temperature range in study: ~2-12°C - Seasonal outdoor winter-swimming water temperatures in Denmark Cooling protocol temperature: 4°C for 4 minutes - Søberg’s experimental hand/cold-water protocol used to assess physiological responses Blood flow to brain reduction: 30-40% decrease - Reported with neck-deep immersion in 0°C water Heat loss increase with head dunk: 36% more heat loss - Compared with immersion up to the neck Heat loss with neck-deep immersion: 11% heat loss from core - Referenced in discussion of head immersion and afterdrop Room temperature study: 19°C vs 24°C vs 27°C - Sleep-room temperatures used in a cited study on brown fat and insulin sensitivity Age-related brown fat change: After age 40, less brown fat is associated with more obesity - Association discussed as a possible age-related trend Gender thermoneutral comfort: Men ~22°C; women ~24°C - Discussed as a reason for sex differences in thermal comfort and study design Winter-swimmer frequency: 2-3 times per week - Typical exposure frequency among study participants Study design rounds: 3 cold dips and 2 sauna sessions per visit - Protocol used by winter swimmers in the study Glucose clearance: Faster 2-hour glucose decline - Winter swimmers cleared glucose faster than controls after a glucose drink Insulin response: Lower insulin production - Observed in winter swimmers during fasting/experimental testing Inflammatory marker: IL-6 increased with IL-10 follow-up - Markers measured to assess inflammatory response to cold exposure PET imaging finding: One participant had zero detectable brown fat - An outlier who shivered early and had control-like metabolic markers

Pivotal Quotes: "You should get uncomfortable cold." — Dr. Susanna Soberg: Her core prescription for effective deliberate cold exposure "If you end on the cold, you force your body to heat up by itself." — Dr. Susanna Soberg: Explanation of why she recommends ending sessions with cold rather than heat "It should be hard because that's the point of it, right? If you enjoy it, then yeah, then I'm thinking something is wrong." — Dr. Susanna Soberg: On the role of discomfort and cold shock in adaptation

Implications: Listeners can use brief, repeated cold and heat exposures as practical hormetic tools for metabolic and cardiovascular health. The field needs more controlled studies, especially on cold showers, women, children, and clinical populations.