Dr. Susanna Soberg is making a case that most people miss: cold exposure isn't about extremes. It's about the minimum effective dose. Her research centers on brown adipose tissue — brown fat — and what it takes to wake it up. The claim is simple but profound: brief, consistent cold exposure activates a metabolically active tissue that most adults barely use, and that activation has cascading effects on insulin sensitivity, energy expenditure, and cellular longevity.
Brown fat isn't like the fat you're trying to lose. It burns energy rather than storing it. When you get cold, it generates heat through a process called non-shivering thermogenesis. The more active your brown fat, the more metabolically flexible you become. Soberg's contribution is quantifying what "enough" looks like — and it turns out to be far less than most people assume.
Soberg's work sits alongside a rich body of research from the van Marken Lichtenbelt group in the Netherlands, who demonstrated that even mild cold — sleeping in a 19-degree room for a month — meaningfully increased brown fat activity in healthy adults. That finding changed the conversation. You don't need an ice bath to get results. You need sustained mild cold more than you need brief extreme cold.
Where Soberg adds nuance is on the water-versus-air distinction. Cold water extracts heat from the body roughly 25 times faster than cold air at the same temperature. That thermal conductivity is why immersion produces such a strong norepinephrine response — two to five times baseline — compared to standing in a cold room. The signal to brown fat is stronger, the hormonal cascade is sharper, and the downstream effects on mood and metabolism are more pronounced.
There's genuine debate about shivering. Some researchers — including work on succinate release during shivering — suggest that the muscle contractions themselves signal white fat to convert toward beige fat. Soberg acknowledges shivering is useful for beginners but notes it's a sign of inefficiency. As brown fat becomes more active, you shiver less because the brown fat is doing the thermal work instead of your muscles. That's adaptation, not failure.
The cold shock protein findings are less contested. RBM3 and CIRBP — two key cold shock proteins — are well-established in the literature as protective against cellular stress. What's emerging now is that RBM3 specifically appears to promote synapse regeneration in the brain, which connects cold exposure research to neurodegeneration prevention in ways that weren't obvious five years ago.
If you're not ready for immersion, start with your sleep environment. Set your bedroom to around 18-19 degrees Celsius and give it a month. That's a real intervention, not a placeholder. If you want the full metabolic effect, add two to three cold water exposures per week — shower, plunge, lake, whatever's accessible — aiming for one to three minutes at a temperature that's uncomfortable but sustainable. The goal is not heroics. The goal is a consistent signal to your brown fat that cold is part of your life.
Here's what I keep coming back to when I read Soberg's work alongside the heat shock protein research: the body has two parallel cellular repair systems triggered by temperature stress. Heat activates HSP70 and HSP90 — proteins that refold damaged structures and clear metabolic debris. Cold activates RBM3 and its family of cold shock proteins, which protect RNA integrity and promote synapse repair. These are not redundant systems. They target different cellular vulnerabilities. Contrast therapy — alternating heat and cold — may be triggering both cascades in a single session. That's not a small thing. That's a complete cellular maintenance protocol wrapped in what looks, from the outside, like a wellness ritual.