Huberman is making a deceptively simple argument here: deliberate cold exposure and uncontrolled cold stress are not the same thing. One builds the system. The other depletes it. That distinction sounds obvious until you realize how many people conflate the two — thinking that shivering through a cold commute is doing the same work as a structured cold plunge. It is not. Intention shapes the physiological response as much as temperature does.
The Radboud University endotoxin study is the cornerstone here, and it deserves more attention than it usually gets. Researchers injected participants with E. coli lipopolysaccharide — a compound that normally triggers fever, nausea, and pronounced immune symptoms. The group trained in Wim Hof breathing showed dramatically attenuated symptoms. Not because their immune systems were stronger in a naive sense, but because the adrenaline spike from the breathing protocol actively modulated the inflammatory response before it could spiral.
That finding changed how immunologists think about voluntary control of the autonomic nervous system. For decades, the assumption was that the autonomic system was exactly that — automatic. Not trainable. Not something you could reach with breath. The Radboud data cracked that assumption open. And the mechanism — controlled hyperventilation driving CO2 out of the blood, shifting pH, activating the sympathetic nervous system deliberately — is replicable in any lab.
Huberman is careful to separate the breathwork protocol from the broader claims that have accumulated around Wim Hof's public persona. That calibration is right. The core study is solid. But extrapolations — that the method cures autoimmune disease, reverses aging, generates superhuman performance — require more evidence. The honest position is: we know the autonomic nervous system is more trainable than we thought. We do not yet know how far that trainability extends.
Three things that actually move the needle in winter: maintain vitamin D (sun exposure drops, and most people's levels quietly crater by January), keep your deliberate cold practice running rather than letting ambient cold substitute for it, and run Wim Hof breathing in the morning on an empty stomach. That sequencing matters — empty stomach reduces the risk of hyperventilation-induced nausea, and morning timing aligns with the natural cortisol peak your body already generates.
Huberman mentions that winter's shorter days reduce vitamin D synthesis, and that vitamin D modulates immune function. What he does not fully develop is that vitamin D also regulates the same inflammatory cytokines that cold exposure and breathwork act on. IL-6, TNF-alpha, the inflammatory cascade — all of these are touched by vitamin D status. So when your levels crater in winter, you are not just losing a micronutrient. You are losing a regulatory layer that cold practice and breathwork help compensate for. The three interventions — sun, cold, breath — are not separate tools. They are overlapping signals to the same underlying system. That is worth understanding before you reach for the supplement bottle.