Is U.S. average body temperature decreasing?

In the US, the normal, oral temperature of adults is, on average, lower than the canonical 37°C established in the 19th century. We postulated that body temperature has decreased over time. Using measurements from three cohorts–the Union Army Veterans of the Civil War (N = 23,710; measurement years 1860–1940), the National Health and Nutrition Examination Survey I (N = 15,301; 1971–1975), and the Stanford Translational Research Integrated Database Environment (N = 150,280; 2007–2017)–we determined that mean body temperature in men and women, after adjusting for age, height, weight and, in some models date and time of day, has decreased monotonically by 0.03°C per birth decade. A similar decline within the Union Army cohort as between cohorts, makes measurement error an unlikely explanation. This substantive and continuing shift in body temperature—a marker for metabolic rate—provides a framework for understanding changes in human health and longevity over 157 years.

That is from a new paper by Protsiv, Ley, Lankester, Hastie, and Parsonnet.  Via the excellent Kevin Lewis.


It's the Negative Flynn Effect for Body Heat.

I would have guessed the combination of older demographic and higher obesity rates, both of which are signs of slower metabolic rate, but the study claims to have adjusted for that. My next guess is less physical activity not only at the workplace but also at home. Modern conveniences mean less physical exertion and that's not a bad thing.

Modern conveniences mean less physical exertion and that's not a bad thing.

That coincides with the most important daily goal in America, to be able to park the SUV as close to the front door of whatever building Mr. or Mrs. health club member must enter. Employee of the month gets to park next to the boss, right by the front door. Also to provide special parking rights for "handicapped" drivers, who need no physical exercise. Washers and driers mean that Mrs. Middle Class doesn't have to make that excruciating trip out the clothesline to hang up her "Save the gay, baby whales" T-shirts.

Goals af,

"The two-toed sloth... has the lowest and most variable body temperature of any mammal, ranging from 74 to 92 degrees Fahrenheit."

Global cooling. Surely the left has a tax or repressive law that will promise to fix this non-problem.

Long beaked echidnas are 68-86. A tie. Mind you, they are less "mammally" than sloths.

Obesity, or just high body mass in general, causes a HIGHER metabolic rate, not lower.

It is due to the massive increase in consumption of polyunsaturated fats, which are well known to reduce metabolic rate, and are clearly linked to cancer and heart disease. Mas produced seed oils basically didn't exist 150 years ago and most fat consumption was highly saturated dairy or monounsaturated like from olives. Hog and beef fat was also more highly saturated as "finishing" animals with corn and soy was relatively rare. Now Americans guzzle polyunsaturated fats like soy/corn/canola oils that effectively didn't exist until the 20th century and steadily became more and more common.

Cold blooded Americans has always been truth not fiction.

It's much more likely thermometers have become more accurate.

Larger people tend to have lower body temperatures and Americans have gotten larger. Also, they've become more sedentary.

Mammals species tend to have lower body temperature with increasing mass, but not for animals in hot environments where inability to easily get rid of heat can result in higher body temperatures among larger animals. Hug a camel and you'll see what I mean.


Ooh, yeah, maybe I should have suggested hugging an Australian camel. They are mostly tick free. In North Africa the camel tick situation can be revolting. Normally they prefer camels. Maybe you have an unusually high body temperature and they got confused?

"It's much more likely thermometers have become more accurate."

Mercury thermometers are a simple, highly accurate technology that has been around since the 18th century. The current state of the art doesn't improve much on them.

Even if there were inaccuracy, since there are tens of thousands of observations, random errors would not affect this. Only systematic error could produce these results erroneously. This seems unlikely, and they have addressed it, as well.

Mercury thermometers were outlawed about half a century ago. maybe it's the current measurements that are more inaccurate.

Wow. That's impressive. Most countries only got serious around 2015 and a compete phase out global is scheduled for 2030. Glad to see the US was taking the lead in this area in protecting the health of its citizens.

No, there has not "been a generation long effort to get the American government out of the business of protecting the health of its citizens." All those regulations, "lead, sulfites, food labelling coming instantly to mind" are still in effect and no one is attempting to repeal them. However, many people feel the marginal benefit of NEW regulations is small.

It is dishonest to confuse that with "getting American government out of the business ..."

Talk to Alex about it.

Or basically anybody who has ever made a contribution to AEI, Citizens for Prosperity, Mercatus Center, etc. in the last generation.

According to the EPA website, a few states have banned mercury thermometers within the 21st century. However, they are still not banned everywhere. I'm not sure what the "half a century" claim is about.

In any case, modern thermometer technology is good regardless, so it doesn't really matter. The point about mercury is that old readings should be accurate, too.

The authors address this in the abstract: "A similar decline within the Union Army cohort as between cohorts, makes measurement error an unlikely explanation."

If we're talking only tiny differences like .03 degrees could thermometers vintage 1860 even measure at that scale?

Surely no. You must be looking at the average of a bunch of measurements that say "98," "99", "99," etc. Maybe it's a change of rounding methodology in the medical field, or a difference in how they print the lines on popular thermometer brands?

Maybe there was a higher background rate of fever inducing illness in the past?

Yeah, I also wondered about the rate of low grade infection, and so fever, at earlier times.

Readings which are >39C, or which have a diagnosis of fever, are excluded. However, I suppose that if you have more fevers, you would likely have more borderline high temperatures as well.

Whether this is a plausible explanation could be assessed by looking at the rate of fever readings in their data over time.

I'm thinking less systemic inflammation. As death rates from cardiovascular events drop, you're bound to see less inflamed arteries in the general population. Whether that's due to better diet or fewer pollutants, it's the sort of thing you'd expect to see.

Weren't cardiovascular problems less prevalent in the distant past? I recall reading that autopsies of civil war era folks rarely showed arterial deposits, that that changed over the next fifty years or so, and that it was headed back down again. At the time, I recall the medical speculation was that it had to do with alcohol - the more of that you have the less atherosclerosis.

This is way outside my area of expertise, so take it with a grain of salt.

These are not unconsidered. They looked at the impact of month of year and ambient temperature, as well as time of day. If something like you suggest was driving the results, then it should have shown up in these variables.

Yes, I understand the difference.

Ambient room temperature is generally not available. However, if the trends you describe are driving the findings, that should show up in effects related to time of year or ambient outdoor temperature--since room temperature, dress, etc. would be related to these things.

More proof we are turning into a nation of snowflakes.

I did some snowshoeing a couple days ago. I did it in a flannel shirt, in the 30s. Everyone else had at least who layers.

I *think* it's because I'm outside enough that my body is tuned to "turn on the heater."

Either that or my metabolism is whack, I don't know.

(1st to the top!)

We're all becoming

Because of our politics

Cold blooded


That's what I thought: More evidence that the lizard people are taking over.

Not really related, but there's a tv commercial run often in which a couple is riding in their Lexus and realize Mom has come to visit earlier than expected. So what does the couple do? Contact Alexa (or whatever) via the Lexus wi-fi and instruct Alexa to adjust the thermostat, start the coffee, and turn on the lights. And Peter Thiel is disappointed that tech hasn't produced a flying car! This commercial captures perfectly the utter nonsense that is tech. Our body temperatures are going down because tech.

Was demo'd at CES this week. Won't be available until 2023, but the prototype is done. Looks like a giant drone.

Because I have long advocated that all wireless telephones come equipped with a colonoscopy app, I am attentive here to the fact that the only data provided come from ORAL measurements.

Obviously, the thermal status of Americans could be gauged accurately by measuring oral temperature and rectal temperature both, for which a separate wireless phone app could easily be devised.

Elizabeth Holmes is working on it.

The last time I bought a mercury thermometer, which described itself as "for oral or rectal use,” I remember thinking that I was going to have to commit to one or the other up front.

The lizard people are multiplying

"That which burns twice as bright burns half as long"
-- Lao Tzu (quoted by Tyrell in the movie Blade Runner)

Almost all chemical and biochemical processes work faster at higher temperatures, including those that destroy us through aging. The human species may be evolving to better live in a world where there is less need to react quickly to danger, and more rewards to living longer.

Ambient temperatures discussed on pages 6-7. Seems in accord with my initial guess -- as populations urbanize they spend more time indoors. Authors discuss/mention possible reductions in daily ambient temperature fluctuations, air-conditioning, etc.

Fewer infections?

They say that measurement error is unlikely, but what is the margin of error on a body temperature measurement?

Blame Sinatra and the Rat Pack, then the hippies and later the Fonz. Everybody is learning how to be cool.

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