What Cold Water Can—and Cannot—Tell Us About Metabolic Health

1. Guest Background

Dr. Susanna Søberg joins Andrew Huberman on Huberman Lab Essentials to examine a practical scientific question: can changing the temperatures people encounter alter the way their bodies produce heat and regulate metabolism? Her contribution centers on brown fat, muscle shivering, and research involving winter swimmers who also use saunas. This is a discussion of physiological responses and study interpretation, rather than an account of competitive swimming.

Søberg says she began the winter-swimming research in 2016. The starting question was whether an activity people could actually undertake would activate brown fat, and whether its cold stimulus would be too strong, too weak, or sufficient to produce meaningful responses. Her relevant experience in the episode includes recruiting established winter swimmers and comparing their measurements with those of controls.

She also describes conducting a hand-cooling experiment, measuring blood pressure and heart rate and using infrared imaging to examine temperature changes near the clavicles. These specific investigations provide the background for her explanations. The supplied evidence does not identify an institutional affiliation or provide a complete professional biography; the strongest introduction to her here is the research she describes and the questions it can address.

2. What the Episode Covers

The conversation begins with the immediate experience of cold. Søberg describes an uncomfortably cold stimulus as producing cold shock: sympathetic nervous system activation accompanied by catecholamine activity, gasping, and faster breathing. She says the breathing response can diminish as someone becomes accustomed to repeated exposure. That distinction matters because the initial intensity of the experience and the body's later adaptation are different parts of the discussion.

Huberman asks how showers, immersion, and cold outdoor air compare. Søberg emphasizes the amount of skin exposed and the medium making contact with it. In her account, immersion stimulates skin cold receptors more rapidly and extensively than walking in cold air. The episode therefore treats exposure as more than a temperature reading: coverage and form also help determine the stimulus.

Brown fat supplies the central metabolic explanation. Søberg describes signals from skin cold receptors reaching the hypothalamic temperature-regulation system, with noradrenaline-related signaling activating brown fat. Muscles contribute another source of heat through shivering. Her account presents heat production as a collaboration between tissues. For showers, however, she makes an explicit qualification: although she expects brown-fat activation, studies have not quantified how much activation a cold shower produces. A proposed pathway does not supply a measured benefit for every version of exposure.

The most concrete findings concern swimmers with two to three seasons of experience. They generally attended two or three times weekly, completing three cold dips and two sauna sessions on each visit. Dips lasted approximately one to two minutes; sauna rounds lasted ten to fifteen minutes at about 80°C. The outdoor water varied, from around 15°C downward, averaging approximately 2–4°C at its coldest. This was an established pattern of alternating cold and heat, rather than a single exposure imposed on beginners.

Søberg reports that these swimmers had lower insulin than matched controls on two cooling days and one thermally comfortable day. Participants had fasted for eight hours and were measured while lying still. A glucose-drink test added an important companion finding: the swimmers cleared glucose faster and had lower glucose after two hours, despite releasing less insulin.

The familiar weekly totals emerged when the researchers calculated the swimmers' exposure: eleven minutes of cold water and fifty-seven minutes of sauna, spread across two or three visits. Søberg uses these figures to argue that prolonged cold-water swimming is unnecessary to discuss the favorable measurements in her study. Their origin nevertheless remains essential: they describe what this group did, rather than the result of a comparison establishing the best possible schedule.

3. Core Views: Reasoning, Examples, and Limits

The interview's strongest idea is that temperature adaptation deserves attention as a physiological process. Its strongest caution is that explaining that process does not establish every proposed health outcome. Søberg uses hormetic stress—the idea of adaptation to a manageable challenge—to connect repeated exposure with improved heat production and a less pronounced acute stress response. In that account, becoming less breathless on entering cold water need not mean that thermoregulatory adaptation has disappeared. She draws on exercise as an analogy for preparing the body for another challenge. The analogy helps explain her reasoning, but cannot establish equivalent benefits or make cold exposure a substitute for exercise.

The winter-swimmer comparison illustrates both the value and the limits of the evidence. It concerns people already adapted to winter swimming, using sauna as well as cold water in a changing outdoor environment. As described, the comparison does not separate the effects of cold, heat, their alternation, and differences the participants may already have had. It supports reporting the group's metabolic measurements. It does not show that cold water alone caused every difference, or that a beginner following the same weekly total would reproduce them. Nor does calculating eleven minutes establish a minimum effective dose: identifying a threshold would require evidence comparing exposures rather than simply totaling them.

A bedroom-temperature example broadens the discussion beyond dramatic plunges. Søberg recounts a study moving participants through months at 24°C, 19°C, 24°C, and 27°C. She reports improved brown-fat and insulin-sensitivity measures during the cooler month, followed by reductions as the environment warmed. Within her argument, the example suggests that adaptation can respond to sustained environmental conditions and can recede when those conditions change. It does not establish a universal bedroom setting. Participants wore clothes and used duvets, so room temperature was not the temperature of all their exposed skin. Huberman suggests facial cooling as an explanation, and Søberg considers it plausible; the conversation does not present a separate test of that mechanism.

Her hand-cooling experiment makes another useful distinction. She describes four minutes with a hand in 4°C water and a subsequent rise in temperature near the clavicular brown-fat region on infrared imaging. This is an example of a rapid response to localized cooling. It is not a measurement of long-term fat loss. Regional surface temperature, brown-fat activity, the amount of brown-fat tissue, and whole-body metabolic outcomes answer different questions. The episode provides no basis for converting that temperature response into a promised amount of weight loss.

Ending on cold is similarly persuasive at the level of mechanism without being established as a superior protocol. Søberg argues that self-rewarming keeps brown fat and muscles engaged in heat production. Yet she also explains afterdrop: core temperature can continue falling after someone leaves the water as blood circulates through still-cold peripheral tissues and returns toward the core. Her favorable discussion of shivering is conditional on avoiding excessive cooling and staying too long in the water. Shivering therefore cannot serve as a simple score in which more means better. The episode presents no direct cold-ending versus warm-ending comparison that quantifies an additional benefit.

The largest inferential jump concerns disease prevention. Søberg reports increased IL-6, discusses IL-10 and an anti-inflammatory interpretation, and extends the argument to possible prevention of type 2 diabetes, depression, anxiety, and Alzheimer's disease. The discussion supplies no disease-incidence outcomes establishing those effects. A proposed biological route remains different from demonstrated clinical prevention. That distinction also helps place her closing qualification in context: precise longer-term outcomes for fixed temperatures and durations remain uncertain, and she does not consider constantly adding ice necessary. Her enthusiasm for adaptation should be read together with that unresolved dose question.

4. Learning and Application

A useful application of this episode is to improve how exposure recommendations are read. Before adopting a weekly number as a target, reconstruct the conditions behind it: who participated, how experienced they were, how often they attended, how long each round lasted, what temperatures they encountered, and whether heat and cold were combined. The swimmer study contains all these dimensions. Keeping only its eleven-minute total discards information needed to understand what was observed. Combining that time into one long immersion, or removing sauna while expecting identical results, changes the exposure being discussed.

For someone comparing accessible forms of temperature variation, the episode offers possibilities rather than a conversion table. Søberg discusses cold air and cooler sleeping environments alongside showers and plunges. That makes an expensive plunge unnecessary as an entry point to the subject. It does not make the alternatives interchangeable. A shower exposes skin differently from immersion, and its brown-fat effect remains unquantified in her account. Likewise, the bedroom study's 19°C setting belongs to an experiment involving clothes and bedding; it does not demonstrate that a colder room would produce a larger benefit. Convenience, tolerability, and closeness to the studied conditions are separate considerations.

The glucose findings also offer a practical lesson in evaluating health claims. Lower insulin was accompanied by faster glucose clearance. The relationship between those observations is what makes the result relevant to the episode's discussion of insulin sensitivity. Extracting only the lower insulin figure turns a paired finding into a different claim. When assessing a program or product that cites this interview, ask which outcome it actually promises and whether the supporting evidence measures that outcome. Feeling invigorated, noticing warm skin, or shivering cannot by themselves establish the same thing as a glucose-related measurement.

A further boundary concerns self-rewarming. The rationale for ending on cold explains why Søberg recommends it, but does not supply a safe temperature or duration for every person. Her emphasis on short exposures and changing temperatures should discourage treating accumulated minutes, added ice, or prolonged discomfort as achievements in themselves. The afterdrop discussion makes the period after leaving the water relevant, too: exit does not necessarily mark the end of cooling. None of these observations justifies deliberately extending shivering to chase a presumed metabolic return.

For writers, coaches, or readers evaluating the evidence, three questions keep the discussion usable: what did the guest report observing, how did she propose explaining it, and what comparison is still missing? The swimmers' measurements answer the first question. Her self-rewarming rationale addresses the second. The optimal dose and the relative benefits of different ending strategies remain questions for the third. This approach preserves the interview's practical interest while keeping expectations proportional to what was actually described.

Source

• Original episode: Essentials: Cold & Heat Exposure for Metabolic Health | Dr. Susanna Søberg