Heat Myths and Warnings

It’s summer, and the news is full of dire warnings about heat. Mostly justified, but some based on myths debunked all the way back in the 1940s.

In case you haven’t heard, it’s going to be hot here in Portland. As I’m writing, my app upped its prediction for day after tomorrow from 113° to 115°.

Most people have never experienced 115°. I have. Actually, it was 125°.

Here are a couple things I learned in the school of hard knocks—things you probably won’t read about in the news.

  • These temperatures will kill electronics. Even turned off, in the shade. Believe the owner’s manual when it gives a maximum operating temperature and maximum storage temperature. These are real.
  • At 110 °and higher, a breeze isn’t your friend. The hot air imparts more heat to your skin than it removes by facilitating evaporation. It’s a weird experience, but also very real.
  • Believe it or not, the coolest, most comfortable clothing is long sleeves and long pants, loose (the looser the better), and light-colored. The desert-dwelling Bedouin have a mantra: dress to keep the heat out. Why do we think we know better than people who have lived in these conditions for untold generations?

A bigger issue is hydration

Pretty much everything you read says that keeping well hydrated is your defense against heat. This is wrong. It’s based on a mistaken belief that dehydration causes heatstroke.

Heat causes heat stroke. Heat also causes dehydration, so the two sometimes go in tandem. But dehydration in and of itself does not cause heatstroke, unless you are so dehydrated that you run out of fluids to sweat out.

If you want hundreds of pages of details on this, check out Waterlogged by South African exercise physiologist Tim Noakes, known to runners for his encyclopedic tome, The Lore of Running. It’s a fun read, but a shorter answer comes from research done during World War II by E. O. Adolph, an exercise physiologist who marched volunteers around the desert near Yuma, Arizona, trying to help the Army prepare for the North Africa campaign.

He made several important findings, but the most important for this discussion is that his volunteers could be as much as 7-10 percent dehydrated (the equivalent to a 150-pound person losing up to 7 liters of water), and not suffer anything worse than becoming grumpy, thirsty, tired, and eventually refusing to budge. Given water and a rest, they were perfectly ready to go again the next day.

So, stay hydrated to avoid becoming grumpy, thirsty, tired, and otherwise miserable. But don’t count on it to stave off heatstroke. (Though, drinking a quart of cold water can lower your core temperature by a full degree, simply from the heat it absorbs as it warms up.)

Finally, be aware of the risk of hyponatremia, a potentially deadly condition created by low sodium in your bloods. Most reports about it involve people who take “hydrate, hydrate, hydrate” too seriously and drink too much. But it can happen even if you don’t excessively hydrate, because the fluids you drink (even sports drinks like Gatorade) contain less sodium than you are sweating off. The result is that you can actually dehydrate but flush enough sodium out of your body to become hyponatremic.  

This is not myth. I’ve seen it happen to an elite athlete in a hot-weather marathon. Luckily, my marathoner had salt tablets in her kit. Two of those and she perked up with amazing rapidity.

Runners and the media always talk about electrolytes. But in the short run, the one that really matters is sodium. A big hit from the salt shaker can do the trick. I’ve even been known to put a couple of salt packets from a place like McDonald’s in a plastic bag in my pocket, so I have them if needed.

Finally, be aware of the symptoms of heat stress. Many are subtle, but one of the most important is that if you feel chilled on a hot day, it’s a sign of impending heatstroke. Stop what you’re doing and get out of the heat ASAP.