How to Use Cold & Heat Exposure to Improve Your Health | Dr. Susanna Søberg
Dr. Susanna Søberg, PhD, is a researcher focused on how cold and heat exposure affects human physiology. In this discussion, she highlights the remarkable benefits of cold and sauna therapies for metabolism, hormone balance, and inflammation reduction. She reveals how deliberate cold exposure can enhance mood and energy by triggering neurotransmitters. The conversation also touches on the unique responses to cold in men and women and the significant health advantages of brown fat activation. Practical tips and cultural insights from Denmark add a fascinating layer to the discussion.
Top snips
What happens when you hit cold water
10:31 – 14:20
Jumping into uncomfortably cold water triggers a rapid cold shock: sympathetic activation, faster breathing, and release of catecholamines (norepinephrine, epinephrine, dopamine).
This is a powerful arousal signal — useful for mood, alertness, and metabolism, and it subsides with adaptation as you train cold resilience.
If you enjoy it, then yeah, then I'm thinking something is wrong.
— Susanna Søberg
Shower vs. Plunge vs. Cold air →→
18:11 – 20:40
All cold on the skin activates brown fat, but immersion (water up to the neck) is the most potent because water transfers heat faster.
- Cold shower: intermediate effect (less studied)
- Outdoor cold/wind: effective and practical
- Even hand in cold water activates brown fat quickly
Small exposures can still shift metabolism.
Brown fat: plastic, powerful, protective
39:39 – 48:10
Brown adipose tissue (BAT) is rich in mitochondria and plastic — it grows or shrinks with cold exposure and adrenergic signals.
BAT takes up glucose & fatty acids, raises metabolic rate, and improves insulin sensitivity.
You can increase BAT by repeated cold or by sleeping cooler (e.g., 19°C for weeks).
Shivering, afterdrop & why end on cold →
25:22 – 27:50
Shivering boosts metabolism and helps warm you, but watch the “afterdrop”: when vasoconstricted blood returns to core after warming, core temp can fall and trigger shivering.
Ending a session on cold forces your body to re-warm itself, extending thermogenic and neurotransmitter effects (the “Soberg principle”).
The winter-swimmer study — design & real-world protocol
1:01:12 – 1:20:09
Susanna studied experienced winter swimmers (2–3 seasons) vs. matched controls using PET/MRI, biopsies, ECG/EMG and metabolic tests.
Typical routine: 1–2 min cold dips + sauna rounds (10–15 min) × 2–3 sessions/week — practical, field-realistic, and ethically safe for humans.
Key outcomes & dosing: small dose, big benefit
1:27:56 – 1:34:56
Results: winter swimmers had better insulin sensitivity, faster glucose clearance, lower insulin output, and BAT activation.
Susanna’s practical weekly targets: ~11 total minutes cold (many short dips) and ~57 total min sauna (≈10–15 min/session). Short, repeated exposures keep the stimulus potent.