Podcast Summary: Cold Exposure, Saunas, and Your Health: What the Science Says

Title: ZOE Science & Nutrition
Host: Jonathan Wolf
Guests: Dr. Susannah Søberg & Professor Tim Spector
Release Date: May 15, 2025

Introduction

In the latest episode of ZOE Science & Nutrition, host Jonathan Wolf delves into the intriguing world of extreme temperature exposures—specifically cold plunges and saunas—and their impacts on health and longevity. Joined by Dr. Susannah Søberg, a leading expert in thermal stress research, and Professor Tim Spector, a renowned epidemiologist and co-founder of ZOE, the discussion unpacks the scientific foundations behind these popular wellness practices.

Benefits of Saunas

Cardiovascular Health:
Dr. Søberg explains that sitting in a sauna induces a mild cardiovascular workout by increasing heart rate without physical exertion. "[...] sitting in the sauna for a while, you heat up from the inside and out and you will start to sweat. And if you can sit there long enough for your heart rate to go up, you will have a sweating that will correspond to having a mild workout" (04:38).

Metabolism and Insulin Sensitivity:
Regular sauna use has been linked to improved insulin sensitivity and better glucose clearance from the bloodstream. Dr. Søberg references Finnish cohort studies showing that frequent sauna bathers enjoyed better cardiovascular outcomes and lower mortality rates over 15-20 years (04:52).

Relaxation and Sleep:
Post-sauna relaxation boosts the parasympathetic nervous system, promoting a state conducive to sleep. Dr. Søberg notes, "taking a sauna [...] might be a good tool," emphasizing its role in regulating body temperature to prepare for restful sleep (04:52).

Benefits of Cold Exposure

Brown Fat Activation and Metabolic Health:
Cold plunges activate brown fat, a metabolically active tissue that burns white fat and enhances insulin sensitivity. Dr. Søberg describes brown fat as "the better fat," akin to muscles, increasing metabolism and energy expenditure even at rest (12:17).

Mental Health Improvements:
Cold exposure triggers the release of dopamine and noradrenaline, enhancing mood and cognitive clarity. Studies mentioned by Dr. Søberg indicate that cold plunges can alter brain activation patterns associated with negative emotions, fostering a more positive outlook (37:49).

Research Highlights: Scandinavian Winter Swimmers

Dr. Søberg shares insights from her research on Scandinavian winter swimmers, demonstrating significant health benefits from regular cold exposure:

• Improved Insulin Sensitivity: Winter swimmers showed faster glucose clearance and lower insulin levels post cold exposure compared to non-swimmers (24:34).

• Enhanced Thermoregulation: Adapted swimmers maintained better peripheral warmth and more active brown fat, contributing to overall metabolic health (26:44).

• Routine and Frequency: Participants engaged in cold water immersions totaling 11 minutes weekly and sauna sessions totaling 57 minutes, divided across multiple days (27:22).

Gender Differences in Temperature Exposure

Addressing common misconceptions, Dr. Søberg clarifies that both men and women can safely engage in cold plunges and saunas, though physiological responses differ:

• Women: Possess more brown fat and better vasoconstriction, allowing effective cold defense.

• Men: Have greater muscle mass contributing to heat generation (52:02).

However, women may experience heightened stress during certain menstrual phases, advising moderation and attentiveness to individual hormonal states (52:02).

Cryotherapy vs. Traditional Cold Plunges

The discussion touches on the emerging trend of cryotherapy—exposing the body to extremely cold temperatures for short durations. Dr. Søberg acknowledges its benefits in activating brown fat but notes that traditional cold plunges may offer more potent metabolic stimulation due to hydrostatic pressure (45:06).

Practical Advice for Starting Cold and Heat Therapies

Sauna Use:

• Duration: Start with short sessions (10-15 minutes) and gradually increase.

• Frequency: Aim for 2-3 times per week to balance stress and recovery (56:11).

• Alternatives: Hot baths can substitute for saunas, providing similar metabolic and relaxation benefits.

Cold Exposure:

• Starting Slow: Begin with cold showers (30 seconds) before progressing to cold plunges.

• Breathing Techniques: Use nasal breathing to calm the nervous system; avoid hyperventilating.

• Safety Measures: Always have someone present during cold plunges to ensure safety (40:29).

• Frequency: Similar to saunas, 2-3 times per week is recommended to optimize benefits without overtaxing the body (49:03).

General Tips:

• Listen to Your Body: Progress at your own pace and avoid comparing to others.

• Time of Day: Perform cold plunges during daylight hours to avoid disrupting sleep patterns.

• Face Exposure Hack: Pouring cold water on the face can activate the vagus nerve, offering some benefits without full immersion (55:18).

Safety Considerations

Participants are advised to exercise caution if they have:

• Cardiovascular Conditions: Individuals with heart diseases or unregulated blood pressure should avoid extreme temperature exposures.

• Pregnancy: Cold plunges and saunas are not recommended during pregnancy due to unknown effects on the fetus.

• Medication Interactions: Those on blood pressure medications may experience exaggerated responses and should consult healthcare providers before starting these therapies.

Impact on Gut Microbiome

While the gut microbiome remains insulated from direct temperature changes, Dr. Søberg and Tim Spector discuss how systemic stress responses from saunas and cold plunges can indirectly influence gut health. The release of stress hormones and modulation of the immune system may create a more favorable environment for beneficial microbes, though definitive studies are still forthcoming (35:10).

Notable Quotes

• Dr. Susannah Søberg:

  • "The biggest misconception around extreme temperatures is that women shouldn't cold plunge." (02:24)
  • "You can think about it as tissue in your body which will make sure that you are in the right temperature for your cells in your body to have the right activation and function." (16:14)
  • "Life is stressful, but cold plunges can help your body manage and reduce long-term inflammation." (34:40)

• Professor Tim Spector:

  • "I hate cold plunges, but understanding the science behind them makes me consider trying them." (02:16)
  • "My experience of stepping into freezing water is absolutely awful. I can't imagine why anyone would want to do it." (02:02)

Conclusion

The episode thoroughly explores the scientific underpinnings of saunas and cold plunges, illustrating their multifaceted benefits on cardiovascular health, metabolism, mental well-being, and potentially the gut microbiome. Dr. Susannah Søberg and Professor Tim Spector provide actionable insights, encouraging listeners to approach these practices mindfully and safely to harness their full health potential.

Timestamps

• [00:00] Introduction by Jonathan Wolf
• [01:18] Tim Spector welcomes Dr. Søberg
• [02:24] Misconceptions about extreme temperatures
• [03:19] How saunas affect the body
• [04:38] Saunas as a cardiovascular workout
• [06:10] Why heart rate increases in saunas
• [07:25] Safety concerns with saunas
• [10:32] Effects of cold water immersion
• [12:17] Brown fat explained
• [16:14] Thermogenic tissues
• [24:34] Winter swimmers' research findings
• [35:10] Cold exposure and the gut microbiome
• [37:49] Cold plunges and mood disorders
• [40:29] Starting cold and heat therapies
• [43:24] Combining saunas and cold plunges
• [45:06] Cryotherapy insights
• [49:03] Frequency of cold and heat therapies
• [52:02] Gender differences in cold exposure
• [55:18] Face exposure hack
• [56:11] Final practical advice

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