A few extracts from the (excellent) book: What Doesn’t Kill Us: How Freezing Water, Extreme Altitude, and Environmental Conditioning Will Renew Our Lost Evolutionary Strength by Scott Carney
For at least half a century the conventional wisdom about maintaining good physical health has rested on the twin pillars of diet and exercise. While those are no doubt vital, there’s an equally important, but completely ignored, third pillar – environmental training.
Once you arrive at high altitude, your body automatically produces more red blood cells to compensate for lower oxygen saturation. Move to an oppressively hot environment and your body will sweat out fewer salts over time and produce lower volumes of urine. Heat will also stimulate your cardiovascular system to become more efficient and increase evaporation and cooling. Yet no environmental extreme induces as many changes in human physiology as the cold does.
A plunge into ice-cold water not only triggers a number of processes to warm the body, but also tweaks insulin production, tightens the circulatory system, and heightens mental awareness. A person actually has to get uncomfortable and experience that frigid cold if they want to initiate those systems.
Despite all of our technology, our bodies are just not ready for a world so completely tamed by our desire for comfort. Without stimulation, the responses that were designed to fight environmental challenges don’t always lie dormant. Sometimes they turn inward and wreak havoc on our insides. An entire field of medical research on autoimmune diseases suggests they originate from fundamental disconnect between the outside world and an under stimulated biology.