Below, Bill Gifford shares five key insights from his new book, Hotwired: How the Hidden Power of Heat Makes Us Stronger.
Bill has been writing about health and longevity for about 20 years. He is a co-author of the worldwide bestseller Outlive and, prior to that, wrote the New York Times bestseller Spring Chicken. He is a longtime contributing editor of Outside magazine, and his writing has been featured in Best American Sportswriting.
What’s the big idea?
We’ve been taught to avoid heat, but our bodies were built for it. From boosting heart health and performance to improving mood and longevity, strategic heat exposure is a powerful, overlooked tool for living better.
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1. We were born to sweat.
Sweat has a bad rap nowadays. It’s considered kind of gross, and socially unacceptable. We wouldn’t show up for a dinner date or a job interview soaked in sweat, and we spend billions of dollars trying to stop or hide it. Which is crazy because the average adult human has between two and four million sweat glands spread all over their body. We are sweating machines!
There are two kinds of sweat, and the first is called apocrine—this is the sweat that soaks your armpits and other hairy areas, and it’s also the stuff that produces body odor. The other kind of sweat glands are called eccrine glands, and those are found all over. Eccrine sweat glands cool us down by bringing liquid to the surface of our skin and then letting it evaporate. When we exercise or feel hot, our eccrine sweat glands are activated.
Why do we have so many eccrine sweat glands? I spoke to an evolutionary geneticist named Yana Kamberov who discovered that at some point in our lineage, natural selection basically went crazy with our sweat-gland genes—mutating rapidly over a short period of time, giving us these cooling sweat glands, everywhere. Our ancestors could now forage and hunt in the heat of the day. Some evolutionary biologists believe that our ancestors would use our superior cooling ability to chase down prey animals in the middle of the day, basically running them to death (deer or antelope can only cool down by panting). We are natural-born endurance athletes, and sweating is our superpower.
2. Heat can heal us.
Sweating is good for us. An incredible series of studies out of Finland looked at a group of about 2,500 middle-aged men and found that the most frequent sauna users had less than half the rate of heart attacks, cardiovascular disease, and overall deaths than the infrequent users, and about one-third the rate of Alzheimer’s disease. This is an incredible result, more powerful than any medication, and similar, if not greater, than the effect of exercise. By going to sauna and experiencing intense but limited bouts of heat exposure, they were strengthening their cardiovascular systems, their vasculature, and that made them more resistant to heart disease and probably also Alzheimer’s.
“This is an incredible result, more powerful than any medication, and similar, if not greater, than the effect of exercise.”
Another important change that happens when we get hot is that our cells activate heat shock proteins, which are like the repair department for our cells, helping keep everything running smoothly and making us more resilient to the effects of heat stress. They may even play a role in slowing damage caused by aging.
There are other positive changes that take place in sauna users (also in people who just take hot baths), but what these Finnish studies also did was to change the conversation around heat. Where heat exposure was once viewed as always dangerous, people now see it has the potential to heal.
3. Sweat is like a performance-enhancing drug.
Humans are an incredibly adaptable animal. That’s how we have spread all over the planet. You’ve probably noticed that an 80-degree Fahrenheit day in May feels pretty hot, but in July, that temperature is a relief. That’s because we’ve become heat-adapted, which turns out to be an incredibly powerful tool.
Olympic athletes use heat-adaptation training to compete in hot places like Tokyo and, soon, LA; all kinds of athletes use it, from Tour de France cyclists to dressage horses. Coaches and scientists have found that by raising your core body temperature just a little bit (around 101 degrees Fahrenheit) and keeping it there, your physiology changes in subtle but awesome ways: you sweat more, run at a lower core body temperature, and your aerobic capacity increases.
Heat training is the new altitude training, and you can benefit from it even if you’re not in the Olympics. I used heat training to prepare for a 100-mile bike ride in Texas, in 107-degree weather, called the “Hotter’n Hell Hundred”—and I was astounded how much it helped.
4. Cold kills.
As I was looking into the limits of human heat tolerance, I discovered that the death toll attributable to colder temperatures is far greater (seven to ten times greater) than deaths due to heat. This balance is changing a little with climate change, but it’s still overwhelming. Even in places like sub-Saharan Africa, there are many more excess deaths associated with cool temperatures than with hot temperatures. Why is that?
“Something deep within us craves warmth.”
As our ancestors developed the ability to sweat, they lost most of their fur, which meant they couldn’t keep warm. This is ironic because only then did our ancestors migrate to the Arctic, Siberia, and other inhospitable places. To me, it solves the riddle of why people seem to crave hot spaces—not only sauna, which is a thousands-of-years-old practice, but things like hot yoga, which people seem to get addicted to. Something deep within us craves warmth. And way back, in a premodern era, we would have gravitated to any kind of warm space.
5. Heat can make us happier.
Heat waves are typically associated with an increase in violence, stress, and general grumpiness, but a little group of scientists is making progress using heat therapy as a treatment for depression.
Several studies have now found that whole body hyperthermia—heating people up, to simulate a mild fever—can drastically reduce or even eliminate symptoms of severe depression. I participated in one of those studies as a test subject, and it was no picnic, but I experienced a definite improvement in my level of depression.
Some research suggests that getting hot stimulates certain brain regions to produce more serotonin. But I also think this helps explain the popularity of social sauna; something about getting hot and uncomfortable seems to knock us out of whatever spiral we’re in, making us more willing, more receptive, more chatty, and just generally happier. Nature wants us to get sweaty together.
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