Decreasing human body temperature in the United States

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Decreasing human body temperature in the United States

Post by Woodchopper » Fri Jan 10, 2020 11:52 pm

Yes, human body temperature getting lower.

Not some crazy theory but based on data and with a plausible explanation.

Read all about it here: https://elifesciences.org/articles/49555

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Re: Decreasing human body temperature in the United States

Post by jaap » Sat Jan 11, 2020 12:45 am

I'm a bit confused about the explanations given for this drop in temperature.

In order to rule out that the drop was due to differences in measuring methods over the years, they compared the contemporaneous measurements against each other,and showed that the drop correlated with the birth year. So there is a drop of 0.03 degrees C per birth decade, rather than just per decade.

They claim that the drop in temperature is due to a reduced metabolic rate, and speculate that it is most likely caused by a reduced amount of inflammation in the population as a whole, but also due to better temperature control in buildings.

If the temperature is correlated to birth year, it would suggest that the body temperature (or metabolic rate) is set at birth, so I don't see how the explanations apply. Maybe the temperature/metabolic rate settles when you're young, and that the amount of inflammation affects that. Not so sure the ambient temperature in your youth would have a permanent effect on body temperature later in life though.


P.S. "with a mean body temperature 1.6% lower" Oh dear. That makes me doubt everything.

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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 11:50 am

jaap wrote:
Sat Jan 11, 2020 12:45 am
If the temperature is correlated to birth year, it would suggest that the body temperature (or metabolic rate) is set at birth...
No, birth year could be a surrogate for later things going on that affected temperature, like chronic infections or whatever. These would change over time.

And there''s nothing wrong with that "1.6% lower" statement.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 12:22 pm

GeenDienst wrote:
Sat Jan 11, 2020 11:50 am
jaap wrote:
Sat Jan 11, 2020 12:45 am
If the temperature is correlated to birth year, it would suggest that the body temperature (or metabolic rate) is set at birth...
No, birth year could be a surrogate for later things going on that affected temperature, like chronic infections or whatever. These would change over time.

And there''s nothing wrong with that "1.6% lower" statement.
It would correspond to a drop in body temperature of about 5°C.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 12:50 pm

shpalman wrote:
Sat Jan 11, 2020 12:22 pm
GeenDienst wrote:
Sat Jan 11, 2020 11:50 am
jaap wrote:
Sat Jan 11, 2020 12:45 am
If the temperature is correlated to birth year, it would suggest that the body temperature (or metabolic rate) is set at birth...
No, birth year could be a surrogate for later things going on that affected temperature, like chronic infections or whatever. These would change over time.

And there''s nothing wrong with that "1.6% lower" statement.
It would correspond to a drop in body temperature of about 5°C.
We found that men born in the early 19th century had temperatures 0.59°C higher than men today
That's pretty much 1.6% of 37.6 C.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 1:08 pm

GeenDienst wrote:
Sat Jan 11, 2020 12:50 pm
shpalman wrote:
Sat Jan 11, 2020 12:22 pm
GeenDienst wrote:
Sat Jan 11, 2020 11:50 am


No, birth year could be a surrogate for later things going on that affected temperature, like chronic infections or whatever. These would change over time.

And there''s nothing wrong with that "1.6% lower" statement.
It would correspond to a drop in body temperature of about 5°C.
We found that men born in the early 19th century had temperatures 0.59°C higher than men today
That's pretty much 1.6% of 37.6 C.
But it's only about 1.1% of 99.7°F.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 1:09 pm

Go for absolute and you'll get an even bigger wrong number.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 1:13 pm

GeenDienst wrote:
Sat Jan 11, 2020 1:09 pm
Go for absolute and you'll get an even bigger wrong number.
Like I said, a temperature "1.6% lower" than a usual body temperature would correspond to a drop of about 5°C only the only common temperature scale in which the zero is not an arbitrary definition.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 1:14 pm

Well done on ignoring the context and content of the entire paper.
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Re: Decreasing human body temperature in the United States

Post by Martin Y » Sat Jan 11, 2020 1:35 pm

There was a More Or Less podcast last year about body temperature and whether Wunderlich's 37°C was accurate.

https://www.bbc.co.uk/sounds/play/w3cswk3g

Still available if you have 9 minutes to spare. If not just listen to the last 2-3 minutes when they talk about whether it's an accurate number or not. They don't consider whether humans have changed. They do explain that his thermometers were calibrated to take readings from patients armpits so read a few degrees hotter than modern thermometers.

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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 2:20 pm

jaap wrote:
Sat Jan 11, 2020 12:45 am
I'm a bit confused about the explanations given for this drop in temperature.

In order to rule out that the drop was due to differences in measuring methods over the years, they compared the contemporaneous measurements against each other,and showed that the drop correlated with the birth year. So there is a drop of 0.03 degrees C per birth decade, rather than just per decade.

They claim that the drop in temperature is due to a reduced metabolic rate, and speculate that it is most likely caused by a reduced amount of inflammation in the population as a whole, but also due to better temperature control in buildings.

If the temperature is correlated to birth year, it would suggest that the body temperature (or metabolic rate) is set at birth, so I don't see how the explanations apply. Maybe the temperature/metabolic rate settles when you're young, and that the amount of inflammation affects that. Not so sure the ambient temperature in your youth would have a permanent effect on body temperature later in life though.
The data in Fig. 1A start at age 30.

I think the point is that for a particular person born in a certain year, their body temperature slowly decreases with age. However, for a person born later than this first person, their body temperature starts a bit lower (and then decreases with age).

There's a sentence in the introduction "Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass)" which seems to be contradicted in the outro "studies examining whether metabolism is related to body surface area or body weight (Du Bois, 1936; Kleiber, 1972), ultimately, converged on weight-dependent models (Mifflin et al., 1990; Schofield, 1985; Nelson et al., 1992). Since US residents have increased in mass since the mid-19th century, we should have correspondingly expected increased body temperature."

I think the outro is correct and the idea of accumulating a greater body mass because of a "slow metabolism" as implied by the sentence in the intro is one of those common misconceptions.

(Incidentally, the Stefan–Boltzmann law says that the power radiated from a black body is proportional to the fourth power of the temperature; assuming a spherical human in a vacuum the power difference from the temperature change of 0.59°C would be of the order of 1%. I think you'd get a much smaller difference once you also count the warmth from the surroundings radiating power back into the human, mostly from the inside of your clothes rather than the ambient temperature.)
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Re: Decreasing human body temperature in the United States

Post by Fishnut » Sat Jan 11, 2020 2:45 pm

Martin Y wrote:
Sat Jan 11, 2020 1:35 pm
There was a More Or Less podcast last year about body temperature and whether Wunderlich's 37°C was accurate.

https://www.bbc.co.uk/sounds/play/w3cswk3g

Still available if you have 9 minutes to spare. If not just listen to the last 2-3 minutes when they talk about whether it's an accurate number or not. They don't consider whether humans have changed. They do explain that his thermometers were calibrated to take readings from patients armpits so read a few degrees hotter than modern thermometers.
Thank you for this! When I read the paper it reminded me of something I heard about body temperature being "different" now to when it was first determined and I couldn't for the life of me remember where. It was More or Less.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 2:50 pm

shpalman wrote:
Sat Jan 11, 2020 2:20 pm
There's a sentence in the introduction "Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass)" which seems to be contradicted in the outro "studies examining whether metabolism is related to body surface area or body weight (Du Bois, 1936; Kleiber, 1972), ultimately, converged on weight-dependent models (Mifflin et al., 1990; Schofield, 1985; Nelson et al., 1992). Since US residents have increased in mass since the mid-19th century, we should have correspondingly expected increased body temperature."
There's no contradiction there. BMR increases with body weight. If BMR is a crude surrogate for temperature, then in the absence of other things happening, it is reasonable to speculate that increasing size in the population would predict increasing BMR, which in turn would predict increasing temperature. Even if someone was overweight in part due to a low BMR, the same relationship would be expected apply if they got heavier.

The following sentence, which you didn't quote, is important in the context of their argument:
Thus, we interpret our finding of a decrease in body temperature as indicative of a decrease in metabolic rate independent of changes in anthropometrics.
I would argue with "independent of", because it is likely that multiple things are happening. Something like "not driven by" might be closer to gist of what they are really saying, as the overall direction of the change in temperature they describe is opposite to that expected (indirectly) from contemporaneous changes in adiposity.
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Re: Decreasing human body temperature in the United States

Post by JQH » Sat Jan 11, 2020 4:26 pm

GeenDienst wrote:
Sat Jan 11, 2020 11:50 am

And there''s nothing wrong with that "1.6% lower" statement.
It's every bit as wrong as a tabloid story asserting that 30 degrees Celcius is twice as hot as 15 degrees Celcius.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 5:01 pm

JQH wrote:
Sat Jan 11, 2020 4:26 pm
GeenDienst wrote:
Sat Jan 11, 2020 11:50 am

And there''s nothing wrong with that "1.6% lower" statement.
It's every bit as wrong as a tabloid story asserting that 30 degrees Celcius is twice as hot as 15 degrees Celcius.
These authors haven't done that. They talk about mean body temperature, using the standard SI unit for temperature, and they found it Their measurement was 1.6% lower over time. This is perfectly correct.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 5:13 pm

GeenDienst wrote:
Sat Jan 11, 2020 5:01 pm
JQH wrote:
Sat Jan 11, 2020 4:26 pm
GeenDienst wrote:
Sat Jan 11, 2020 11:50 am

And there''s nothing wrong with that "1.6% lower" statement.
It's every bit as wrong as a tabloid story asserting that 30 degrees Celcius is twice as hot as 15 degrees Celcius.
These authors haven't done that. They talk about mean body temperature, using the standard SI unit for temperature, and they found it Their measurement was 1.6% lower over time. This is perfectly correct.
The °C isn't the SI unit for temperature. Its definition of zero is physiologically meaningless. Ok, it would have been meaningless to give the percentage of absolute temperature difference too, but at least it wouldn't have been physically incorrect.

(It would have been more meaningful to compare the temperature difference to the normal range of human body temperature variations, or something like that.)
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 5:19 pm

GeenDienst wrote:
Sat Jan 11, 2020 2:50 pm
shpalman wrote:
Sat Jan 11, 2020 2:20 pm
There's a sentence in the introduction "Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass)" which seems to be contradicted in the outro "studies examining whether metabolism is related to body surface area or body weight (Du Bois, 1936; Kleiber, 1972), ultimately, converged on weight-dependent models (Mifflin et al., 1990; Schofield, 1985; Nelson et al., 1992). Since US residents have increased in mass since the mid-19th century, we should have correspondingly expected increased body temperature."
There's no contradiction there. BMR increases with body weight...
Yes that's why I didn't understand why they wrote "lower metabolism, greater body mass" in the introduction. All things being equal, if you consume a certain number of calories and require less energy to maintain your body temperature then you will gain weight, but things aren't equal because that gained weight needs more metabolism to support it.
GeenDienst wrote:
Sat Jan 11, 2020 2:50 pm
If BMR is a crude surrogate for temperature, then in the absence of other things happening, it is reasonable to speculate that increasing size in the population would predict increasing BMR, which in turn would predict increasing temperature. Even if someone was overweight in part due to a low BMR, the same relationship would be expected apply if they got heavier.

The following sentence, which you didn't quote, is important in the context of their argument:
Thus, we interpret our finding of a decrease in body temperature as indicative of a decrease in metabolic rate independent of changes in anthropometrics.
I would argue with "independent of", because it is likely that multiple things are happening. Something like "not driven by" might be closer to gist of what they are really saying, as the overall direction of the change in temperature they describe is opposite to that expected (indirectly) from contemporaneous changes in adiposity.
I think they are suggesting that since these effects are opposite then the changes in adiposity slightly counteract the change in temperature which would otherwise be even stronger.
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Re: Decreasing human body temperature in the United States

Post by Woodchopper » Sat Jan 11, 2020 5:31 pm

All the authors work at Stanford and as far as I can tell have PhDs.

One is a Senior Research Scientist
One is a Professor of Medicine (Infectious Diseases and Geographic Medicine) and Professor of Health Research and Policy
One is a Professor of Mathematical Sciences and Professor of Statistics

I doubt that they’d make basic errors that we’d usually associate with a tabloid journalist.

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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 5:39 pm

And yet they thought it was meaningful to say that 0.6°C was 1.6% of 37°C.

If the air temperature dropped from 0.0°C to -0.6°C, what percentage change would that be?
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 5:44 pm

In the introduction they are just pointing out why we they think we should think changes in BMR are important.

Again, the whole paragraph provides better context.
The question of whether mean body temperature is changing over time is not merely a matter of idle curiosity. Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). We speculated that the differences observed in temperature between the 19th century and today are real and that the change over time provides important physiologic clues to alterations in human health and longevity since the Industrial Revolution.
It's not very well written. There's a *clunk* as they go into the last sentence. If t'were me I'd have put some version of the first sentence in at the 3rd sentence, something like

Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). [so it's important, like, yeah?] We speculated...

That would flow better.
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Re: Decreasing human body temperature in the United States

Post by GeenDienst » Sat Jan 11, 2020 5:44 pm

shpalman wrote:
Sat Jan 11, 2020 5:39 pm
And yet they thought it was meaningful to say that 0.6°C was 1.6% of 37°C.

If the air temperature dropped from 0.0°C to -0.6°C, what percentage change would that be?
You have a gift for completely ignoring context.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 5:55 pm

GeenDienst wrote:
Sat Jan 11, 2020 5:44 pm
In the introduction they are just pointing out why we they think we should think changes in BMR are important.

Again, the whole paragraph provides better context.
The question of whether mean body temperature is changing over time is not merely a matter of idle curiosity. Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). We speculated that the differences observed in temperature between the 19th century and today are real and that the change over time provides important physiologic clues to alterations in human health and longevity since the Industrial Revolution.
It's not very well written. There's a *clunk* as they go into the last sentence. If t'were me I'd have put some version of the first sentence in at the 3rd sentence, something like

Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). [so it's important, like, yeah?] We speculated...

That would flow better.
If you go to https://elifesciences.org/articles/49555 and click on "Author Response" you can actually read some of the peer review comments as quote by the authors in their response.
anonymous peer wrote:Given that body temperature is defined as a biomarker for metabolic rate, discussion regarding body habitus in different parts of the manuscript are a bit difficult to reconcile: 1) lower metabolism is associated with greater body mass (Introduction, last paragraph); 2) increased body mass is associated with increased body temperature (Discussion, second paragraph).
The authors don't actually seem to respond to that.
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Re: Decreasing human body temperature in the United States

Post by shpalman » Sat Jan 11, 2020 7:38 pm

GeenDienst wrote:
Sat Jan 11, 2020 5:44 pm
shpalman wrote:
Sat Jan 11, 2020 5:39 pm
And yet they thought it was meaningful to say that 0.6°C was 1.6% of 37°C.

If the air temperature dropped from 0.0°C to -0.6°C, what percentage change would that be?
You have a gift for completely ignoring context.
"Our investigation indicates that humans in high-income countries have changed physiologically over the last 200 birth years with a mean body temperature 1.6% lower than in the pre-industrial era."

It would have been fine if they would have just written 0.6°C instead of 1.6%. There doesn't seem to be anything wrong with the rest of the paper, it's just a silly mistake.
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Re: Decreasing human body temperature in the United States

Post by Martin_B » Sat Jan 11, 2020 10:44 pm

GeenDienst wrote:
Sat Jan 11, 2020 5:44 pm
shpalman wrote:
Sat Jan 11, 2020 5:39 pm
And yet they thought it was meaningful to say that 0.6°C was 1.6% of 37°C.

If the air temperature dropped from 0.0°C to -0.6°C, what percentage change would that be?
You have a gift for completely ignoring context.
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Re: Decreasing human body temperature in the United States

Post by dyqik » Sun Jan 12, 2020 2:48 am

GeenDienst wrote:
Sat Jan 11, 2020 5:44 pm
shpalman wrote:
Sat Jan 11, 2020 5:39 pm
And yet they thought it was meaningful to say that 0.6°C was 1.6% of 37°C.

If the air temperature dropped from 0.0°C to -0.6°C, what percentage change would that be?
You have a gift for completely ignoring context.
There's no possible context in which that statement is meaningful and correct.

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