
Decreasing human body temperature in the U.S. since the industrial revolution - bookofjoe
https://elifesciences.org/articles/49555
======
harry8
Decreasing over time. The following example from Feynman's rightly extremely
famous "Cargo Cult Science" lecture is extremely relevant. Now it may not be
what is going on here at all, but that probably needs to be established
somehow before deciding that some other alternative (eg instrumentation
changes, everyone's actual temperature has changed rather than just its
recording, whatever other theory).

And if you haven't seen it, it's fantastic. As is the whole lecture, 5 minutes
you really won't regret.

"We have learned a lot from experience about how to handle some of the ways we
fool ourselves. One example: Millikan measured the charge on an electron by an
experiment with falling oil drops and got an answer which we now know not to
be quite right. It’s a little bit off, because he had the incorrect value for
the viscosity of air. It’s interesting to look at the history of measurements
of the charge of the electron, after Millikan. If you plot them as a function
of time, you find that one is a little bigger than Millikan’s, and the next
one’s a little bit bigger than that, and the next one’s a little bit bigger
than that, until finally they settle down to a number which is higher.

Why didn’t they discover that the new number was higher right away? It’s a
thing that scientists are ashamed of—this history—because it’s apparent that
people did things like this: When they got a number that was too high above
Millikan’s, they thought something must be wrong—and they would look for and
find a reason why something might be wrong. When they got a number closer to
Millikan’s value they didn’t look so hard. And so they eliminated the numbers
that were too far off, and did other things like that." [1]

Needless to say the actual charge on an electron is very likely to have been
constant over that period rather than trending steadily upward.

[1]
[http://calteches.library.caltech.edu/51/2/CargoCult.htm](http://calteches.library.caltech.edu/51/2/CargoCult.htm)

~~~
Iv
Interestingly, here in Japan, I learned that they consider a lower body
temperature normal. I always learned in France that the normal body
temperature was 37.7C, some people say 37.3. Can be lower just after waking
up.

For my Japanese wife, 37C means you may starting to get sick. you should be in
the 36s.

Just an anecdote, but the normal temperature could vary among population,
latitude, weather conditions...

~~~
brutt
Normal body temperature is 36.6°C (97.9°F) even in France, but can be up to
37°C sometimes or in some places. Temperature of 37.7°C is symptom of
sickness.

[https://www.bmj.com/content/359/bmj.j5468](https://www.bmj.com/content/359/bmj.j5468)

Results:

In a diverse cohort of 35 488 patients (mean age 52.9 years, 64% women, 41%
non-white race) with 243 506 temperature measurements, mean temperature was
36.6°C (95% range 35.7-37.3°C, 99% range 35.3-37.7°C). Several demographic
factors were linked to individual level temperature, with older people the
coolest (–0.021°C for every decade, P<0.001) and African-American women the
hottest (versus white men: 0.052°C, P<0.001). Several comorbidities were
linked to lower temperature (eg, hypothyroidism: –0.013°C, P=0.01) or higher
temperature (eg, cancer: 0.020, P<0.001), as were physiological measurements
(eg, body mass index: 0.002 per m/kg2, P<0.001). Overall, measured factors
collectively explained only 8.2% of individual temperature variation. Despite
this, unexplained temperature variation was a significant predictor of
subsequent mortality: controlling for all measured factors, an increase of
0.149°C (1 SD of individual temperature in the data) was linked to 8.4% higher
one year mortality (P=0.014).

~~~
Iv
I found something super interesting!

The EN and FR wikipedia state different values.

FR:

> On considère généralement que la température basale usuelle du corps humain
> est de 37,0 °C, [...] Une température corporelle normale se situe entre 36,1
> °C et 37,8 °C

Baseline : 37C. Normal range, [36.1 - 37.8]

EN:

No baseline, provided,just a range:

> The normal human body temperature range is typically stated as 36.5–37.5 °C
> (97.7–99.5 °F).

The French version explains that for a long time, until the 1980s, everybody
assumed correct a study made in 1868 about the body temperature that found
37.0 - 37.5 to be the normal range in healthy adults.

It suggests that the declining prevalence of infections in the population may
be the exaplanation of the lowering of the average body temperature.

After all, one of the main causes of rising temperature is an active immune
system. Lower temperatures in the population are actually good news.

------
TallGuyShort
When we're discussing relatively small changes in temperature over very long
periods of time, I wonder how confident we are in those measurements? I mean a
very regular trend like this is a pretty strong signal that you're at least
not overwhelmed by random noise, but: I find it very hard to believe that our
ability to manufacture very precise and accurate thermometers has been so
consistently good (measuring hundredths of degrees) for the order of decades.
Am I wrong? I often wonder how much this impacts climate change studies as
well. Ocean acidification just "feels" like much sounder science to me because
the effects are so much more visible, but I'm not certain about our ability to
measure pH so precisely for decades either.

~~~
5efh456
Due to the way statistics work, you don't need to be able to measure
hundredths of degree to detect a hundredth of degree average change.

Because the error will distribute around the true value, thus even with
sampling errors you can still extract a signal, even a very weak one, if you
have many samples.

~~~
lalaland1125
It depends on the error. It could be that older thermometers were
systematically biased.

~~~
5efh456
Could be.

But surely we have some which survived, or can manufacture using methods of
the time to check.

Also, physics was in a pretty good state at the time, at least regarding
temperature/length measurement. Surely the scientists of the time measured the
bias.

~~~
smegma2
Measuring the bias would require knowing the true temperature.

------
badfrog
From the intro, why this is interesting:

> 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).

~~~
goblin89
> Human body temperature is a crude surrogate for basal metabolic rate

> higher metabolic rate, shorter life span

> lower metabolism, greater body mass

In other words, if you are a really, really skinny person (like myself), you
would be looking at a statistically shorter lifespan, unless somehow your
normal body temp is lower than average or you spot some other sign of
decreased basal metabolic rate. Huh!

I had some intuition along those lines but thought it’s false, and habitually
viewed high metabolic rate as nothing but a “feature” until now.

I suppose, then, you might want to be aware of this if you have a young
family—get life insurance, if you haven’t already (and I also hope, if this
research proves sound, insurers won’t start taking it into account any time
soon).

~~~
mjfl
> if you are a really, really skinny person (like myself), you would be
> looking at a statistically shorter lifespan, unless somehow your normal body
> temp is lower than average or you spot some other sign of decreased basal
> metabolic rate. Huh!

I think you are making the error of combining the "folk" understanding of high
metabolism - that you are skinny, with the scientific understanding of high
metabolism, which means you expend a lot of calories every day. It's more
likely that you have calorically restricted yourself throughout your life to
become skinny, which has longevity benefits, and it's also likely that very
fat people burn a lot of calories every day - high metabolism, worse for
longevity.

~~~
AtlasBarfed
My fundamental question on calorie restriction is that women have been doing
it for superficial reasons for quite a while, but women's superior life
expectancy seems soley due to high risk behavior by men when they are young
and middle age.

I've never seen anything testing that hypothesis.

~~~
yojo
There are actuary tables of average life expectancy given a base age. If you
are a 70 yo female, you’re expected to live 2 years more than a 70 yo male.

[https://www.ssa.gov/oact/STATS/table4c6.html](https://www.ssa.gov/oact/STATS/table4c6.html)

It’s possible this difference is a legacy from riskier makes behavior in
middle age. I can’t think of a reasonable way to control for this though.
Maybe look cross culturally to see if the effect is stable with respect to
different male behavior norms?

~~~
masklinn
> If you are a 70 yo female, you’re expected to live 2 years more than a 70 yo
> male.

The difference is still a year at 86, and doesn't fall to par until
supercentenarians.

------
ivanech
An interesting note: Trevor Hastie is an author on this paper. The crowd
around here probably knows him best for books he co-wrote: The Elements of
Statistical Learning (2001) and An Introduction to Statistical Learning
(2013).

~~~
laichzeit0
It's funny reading the comments in this thread from random internet people
postulating that the authors have probably made some statistical mistake or
overlooked something. Then you see Hastie in the author list. Nope, no
methodological mistakes made here.

------
olex
This is interesting, I didn't know 37° is considered normal in the US. In
Ukraine where I grew up as a child (and I imagine also other post-USSR
countries), 36.6° was always taught to be the norm, and 37° typically
considered an onsetting light fever. However, the typical measurement was
always armpit and not oral - maybe that explains the difference.

~~~
graeme
Interesting. I live in canada, and I never measure 37 or above unless I have
at the least a cold or other sickness.

But when at the doctor nurses will always mention something like 37.2 as not
indicating sickness.

My normal temp is 36.4-36.6ish.

~~~
OJFord
> But when at the doctor nurses will always mention something like 37.2 as not
> indicating sickness.

Note though that they may not be wrong, even if you're sick and you know it
from that temperature alone: 'indicating' is a term of art.

More than just 'based on this it does/doesn't seem to be the case that' it
means that a specific (guideline-given, perhaps regulated) set of criteria
have or haven't been met that tell them whether a certain procedure or
whatever should be ordered.

It doesn't mean they can't also listen to what you're saying, and proceed as
though it was indicated , making a judgement on that basis.

------
11235813213455
Most likely due to most people lifestyle:

\- diet (way too poor in vegetables and fruits which are amazing sources of
nutrients of all sorts, (note: nutrients degrade really fast with
temperature/cooking) that facilitate cell functions, blood circulation, etc..)

\- Over-heating and 'over-clothing': these artificial heating is making our
own natural heating less efficient (people over-heat in winter for example,
it's possible to spend the whole evening and night at 15°C, I live in the
south of France, I don't even heat my apartment, and casually even open
windows at night in winter)

\- Lack of exercise, sun exposure, and quality sleep

------
TheFattestNinja
The article makes, in the discussion section, an hypothesis related to more
time spent in thermally neutral areas as well as better heating and whatnot
due to insulation and AC. Is it possible to formulate a similar thesis for
overall higher ambient temperature linked to global warming?

~~~
semi-extrinsic
That's much smaller though - probably average indoor temperature has gone up
ten degrees easily.

------
ideasarefun
I have to wonder what effect changes in clothing have had over the decades.
The steady trend has been for people to wear less and less clothing since the
1800s, right? But the word "clothing" doesn't appear anywhere in the paper.

I also feel like Amish people living a very old-fashioned lifestyle might make
an interesting control group.

------
ufo
On a related topic, one thing unexpected thing that I learned after I had my
thyroid removed is that there is a LOT of pseudoscience online about body
temperature. In particular, there are plenty of quacks that are eager to
diagnose hypothyroidism if the body temperature comes back as less than 37°C .

~~~
briefcomment
Why do you say that's pseudoscience?

*edit: People are downvoting this without explaining? C'mon.

[https://www.ncbi.nlm.nih.gov/pubmed/29237616](https://www.ncbi.nlm.nih.gov/pubmed/29237616)

~~~
ufo
It is used as an excuse by quack doctors (including naturopaths and
"functional medicine" practitioners) to diagnose people with hypothyroidism
even if all the blood tests come back normal. Here is a good summary:
[https://hormonesdemystified.com/basal-body-temperature-
and-y...](https://hormonesdemystified.com/basal-body-temperature-and-your-
thyroid-why-i-dont-care-and-neither-should-you)

As for the paper you linked, a correlation of -0.013 degrees centigrade is too
small to be useful as a diagnostic tool.

~~~
briefcomment
Good to know

------
DaniFong
This study suggests that from DNA evidence that natural human lifespan is _38_
years old, the same age that was the life expectancy during Wunderlich's 1851
survey.

[https://elifesciences.org/articles/49555](https://elifesciences.org/articles/49555)

Additionally, our heating systems were vastly less sophisticated, and we were
outdoors more.

Together I think that these suggest that we get a sort of genetic gift of our
bodies in our prime, but the growth program kind of peters out in our late
30's. After that it's a genetic maintenance program, with which, in concert
with modern society, we have a good chance to keep the machine going for quite
a long time.

~~~
laurencerowe
The 38 years figure is misleading since it's skewed by high infant mortality
rates. If you made it to 15 then for most of human history you'd probably live
into your 50s or 60s.

~~~
DaniFong
yeah, I think you're definitely right about this, this skews the picture to
your 50's or 60's for sure -- I think that like, human growth hormone levels
also bear this out.

------
allovernow
This might have to do with increasing BMI, though the direction of the causal
relationship could go either, or both ways. I wonder if I can dig up a plot of
average fat composition over a similar period of time. I don't know how
recently we started getting fatter but I suspect it started slowly with the
industrial revolution.

~~~
elil17
They controlled for height and weight in the study

------
hyperpallium
_tl;dr_ speculated causes: reduced inflammation; home heating/cooling

I would have thought more sedentary lifestyle would have decreased resting
metabolic rate, but they didn't mention that one.

~~~
lukeschlather
I don't see them discussing the definition of "resting metabolic rate" in this
paper. I don't know how long it takes the body to reach the "resting metabolic
rate" though I imagine it varies depending on quantity and intensity of
physical activity.

What I'm getting at is that people are more likely to drive to the doctor than
they were in the past, which means they actually were likely at a truly
resting metabolic rate when arriving at the doctor's office. While in the
past, it's more likely people might have walked (or ridden a horse) a mile or
more to the office, which I imagine would result in the "resting rate" to
often not actually be a resting rate but be somewhat elevated.

------
Supermancho
Because medicine has been more and more careful about inflammatory responses,
I propose that the reduction in inflammation (internal and minor) has been a
co-factor.

------
AtlasBarfed
Humans are less active and probably have a reduced basal metabolic rate, which
is where the heat comes from.

That seems the obvious explanation, moreso that disease-related inflammation.

~~~
Enginerrrd
This makes a lot of sense to me.

------
krick
Huh. All my life I knew the rule-of-thumb value of 36.6°C, and I always
assumed 37°C is just a crude rounded-up value of that.

------
fouc
What if overweight people run cooler as well?

------
villmann
In Soviet Union it has always been 36.6

------
alexandercrohde
For those unaware -- men's sperm count has gone down 3% a year since we've
started measuring.

I see these two facts as potentially related and warranting significant
investigation.

~~~
markdog12
Not only that, but testosterone levels have been dropping in men for decades.
Being that testosterone is essential to men's health and well-being, and they
comprise 50% of people, you'd think society would care more about it.

[https://www.forbes.com/sites/neilhowe/2017/10/02/youre-
not-t...](https://www.forbes.com/sites/neilhowe/2017/10/02/youre-not-the-man-
your-father-was/)

[https://uk.reuters.com/article/health-testosterone-levels-
dc...](https://uk.reuters.com/article/health-testosterone-levels-dc-
idUKKIM16976320061101)

~~~
shpongled
Last year I got my hormone levels checked for the first time (normal), and I'm
going to continue to do so yearly to keep track. Given how important it is,
it's really surprising to me that testosterone levels aren't part of regular
health exams/bloodwork panels - I had to convince my doctor add it on.

~~~
JamesBarney
Because the only real fix is giving the patient testosterone which has very
real stroke risks.

~~~
Axsuul
Citation? If you are deficient in testosterone, replacing it is giving your
body what it needs.

~~~
JamesBarney
[https://en.wikipedia.org/wiki/Androgen_replacement_therapy#A...](https://en.wikipedia.org/wiki/Androgen_replacement_therapy#Adverse_effects)

~~~
Axsuul
There are also lots of conflicting studies like this:
[https://www.ncbi.nlm.nih.gov/m/pubmed/26248567/](https://www.ncbi.nlm.nih.gov/m/pubmed/26248567/)

------
kitten_smuggler
Perhaps this can be partially explained by measurements becoming more precise
over time?

~~~
machello13
The abstract, which is only 4 sentences long, explains that they considered
this and dismissed it as unlikely.

------
rjkennedy98
I have a weird feeling this has to do with higher alcohol consumption in the
older days. I wonder if there are many other heavy drinkers who have a high
body temperature like myself.

~~~
throwaway_tech
Although alcohol carries a reputation for keeping people warm when its cold,
it actually has the opposite effect and lowers body temp. But you know...if
your gonna be cold, better to be a little colder and drunk than cold and
sober.

~~~
HorstG
Alcohol cools by widening the blood vessels in your skin and extremities. This
makes you feel warmer, yet it lowers your overall average and core
temperature. This is what makes alcohol in cold weather so dangerous: it
really helps your cold fingers and makes you feel better, while actually
making you worse off by wasting heat.

