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Cold temperatures kill more Americans than hot ones, CDC data show

Bundle up. (Richard Tsong-Taatarii/Star Tribune)

The polar vortex is back with a vengeance in certain parts of the country this week. Here in northwest Minnesota, Saturday's temperature is expected to top out at minus-10 degrees, with a low of minus-27 on Saturday night.

Once you factor in wind chill, the temperature will feel like minus-45 or so. As the National Weather Service helpfully reminds us, in these temperatures “frost bite can occur quickly and even hypothermia or death if precautions are not taken.”

Personally, I'll take crazy cold over crazy heat any day — you can always add layers if you're cold, after all, but if you're hot once you're buck naked there's really not much more to do. But data from the Centers for Disease Control and Prevention has consistently shown that excessive cold presents a greater threat to life than excessive heat. Take a look at the chart below, plotting annual deaths from hypothermia (too much cold) and hyperthermia (too much heat) in the United States from 1999 to 2015.

As you can see, cold deaths outnumber heat-related deaths in just about every year. Part of the disparity may be because of differences in how the human body responds to heat and cold, as outlined in a study in the Lancet released last year. With heat, there may be a “threshold” temperature beyond which the body's temperature regulating system essentially breaks down.

If the temperature is below that threshold (which likely varies between individuals), your body is essentially good to go. It's only when ambient temperatures surpass that point that mortality risks come into play.

With cold temperatures, on the other hand, the authors of the Lancet study posit that it seems to produce negative health effects in a fairly linear fashion. There's no threshold; rather, the colder it gets, the more trouble your body has adapting.

In their study, the authors found that many deaths attributable to cold happened on moderately cold days (as opposed to extremely cold ones), while a much larger share of heat-attributable deaths happened on days of extreme heat — hinting at the threshold relationship mentioned above.

A report published by the CDC a few years ago describes some of the factors in heat and cold-related deaths stateside. One big predictor of temperature-related mortality is age: older people are much more likely to succumb to heat or cold than younger Americans.

There's an economic component, too: “weather-related death rates were 2 to 7 times as high in low-income counties as in high-income counties,” the CDC found. Poorer households may be less likely to have temperature-regulating niceties, such as air conditioning or insulation, that many folks take for granted.

And as you might expect, there's a geographic element, too. Here's a map of hypothermia death rates by state from 1999 to 2015. In this map and the one that follows, the CDC suppresses the data for a number of states. This happens only in cases where there are fewer than 10 deaths across the time period for that state.

As you might expect, Alaska is head and shoulders above all the other states when it comes to hypothermia mortality risk. The age-adjusted rate of 2 deaths per 100,000 population is more than twice as high as the next-highest states, Montana and New Mexico. The northern Plains states stand out on this map, as does New England to a lesser extent.

Here's the map for hyperthermia, or death from excess heat. A number of states are suppressed here — you wouldn't expect to see a lot of heat-related deaths in Maine or Alaska, for instance.

Arizona is the state with the greatest hyperthermia death rate, at 0.7 deaths per 100,000 population. Nevada is similarly high, and a cluster of states in the south-central United States are above average as well.

Overall, the important thing to remember is that your odds of dying from heat or cold exposure are pretty low, even in a polar vortex. In 2015, for instance, a little over 800 people in the United States died from hypothermia. By contrast, over 4,000 people died from drowning, 35,000 were killed by falls and 36,000 died in traffic accidents.

But deaths from cold exposure do happen. Just a few days ago in St. Paul, Minn., a 34-year-old woman died of hypothermia just steps from her house.