Decreasing human body temperature in the U.S. since the industrial revolution | Hacker News Reader

Decreasing human body temperature in the U.S. since the industrial revolution

elifesciences.org

209 pointsbookofjoe143 comments

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

In the case of Millikan's experiment, we are considering something in the order of a dozen repetitions. With these temperature measurements, there are thousands. This alone makes it rather implausible that we have a false signal that is the consequence of an initial error.

Furthermore, unlike with the charge of the electron, there is no strong reason to believe the value is a constant. In fact, it is known to be variable, and that variability has been recognized as diagnostic (which is why we have a lot of measurements.)

As others have pointed out, the authors have considered, in detail, several conceivable sources of systematic error. We probably should not approach studies with the expectation that the people performing them are naive.

I wholly concur that we should assume competence in the researchers and their stated confounding factors.

That said I think skepticism is always healthy when done in good faith and is a driving factor in increasing our knowledge.

That's an interesting phenomena, but it is definitely not what has happened here. The introduction talks about it a bit, but the discussion really gets into it showing why it cannot be measurement error.

I agree. My favorite part is when they examine average temperature by birth decade within each cohort, under the assumption that differences in birth decade will not affect the accuracy of the measuring technique.

> To minimize these biases, we examined changes in body temperature by birth decade within each cohort under the assumption that the method of thermometry would not be biased on birth year.

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...

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

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).

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.

In USSR/Russia 36.6C has always been considered ideally normal (and until this very moment i thought that it was normal for the whole human race :). The same way - crossing 37C means you're sick.

It probably may also depend on where the temperature is taken. In USSR/Russia it is in the armpit, which is probably of lower temperature than anus/mouth which is where the temperature is taken in many other countries.

That has me wondering how much average height and square-cube law implications like surface area ratio changing what they consider "the norm" has to do with it.

BMI as a health metric is downright lazy mathematically in that it doesn't use a cubic portion and thus gives more undue "slack" in its judgement for shorter and less for taller.

I am uncertain what aspect if any dominates. It could be that without sufficent HVAC exposure the local climate causes the body to adapt and dominate. Granted not allowing that adaptation may not just be "softness" and "disconnection from nature from arrogance". Apparently according to some accounts colonialists in the tropic were looked upon by natives as fools and lunatics for being physically active during the hot and bright sun instead of resting then and saving activity for when it is cooler.

> viscosity of air

Why were people not able to find this error?

Eventually they did. If you're asking why it wasn't found sooner ... maybe it was hard to notice?

Perhaps it was due to lack of tight control of variables like humidity and temperature nor the ease of processing repeated experiments across many conditions, especially if they never recorded those variables.

That sounds an awful lot like updating our prior beliefs based on data a la Bayesian modeling. So it's actually not a terrible way to go about updating noisy estimates.

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.

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.

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

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.

Measuring the bias would require knowing the true temperature.

They accounted for that possibility:

> One possible reason for the lower temperature estimates today than in the past is the difference in thermometers or methods of obtaining temperature. To minimize these biases, we examined changes in body temperature by birth decade within each cohort under the assumption that the method of thermometry would not be biased on birth year.

I think that the assumption that the method of thermometry is not biased based upon birth year is probably correct.

> I wonder how confident we are in those measurements?

Very.

Thermometer calibration occurs around known values. Like the melting point of ice and boiling point of water at STP. It’s possible for individual measurements to be off significantly, but long term trends like this cover a huge range of manufacturers so the calibration points would need to be shifting around.

If you measure the temperature of boiling water, it can be noticeably different from 100 degrees depending on the weather and location. The confidence isn't coming through to me still.

I'll buy that equipment exists that can measure temperature extremely accurately, maybe we even base it on the Plank constant now too. But I don't buy for a minute that most thermometers, or anything close to that, are even on the same playing field. Nevermind thermometers from decades ago.

He said “STP” or “standard temperature and pressure”, which controls for the things that affect the measurement changing.

Even if the effects were not properly accounted for in the calibration of thermometers (which I doubt, in general), it would not likely cause a systematic error that shifts slowly over decades. The authors of the report have identified, and explored, other, more plausible souces of such systematic errors, such as in how the measurements are performed.

Do you not own a barometer? Pressure changes by the hour.

Indeed it does, but I cannot see how that could possibly refute the point I am making. How could that cause a systematic error that shifts slowly over decades?

FWIW quartz thermometers achieved accuracies better than 0.05 K in the 60s, with resolution better than 1 mK.

Boiling water is at 100C at standard pressure full stop. It is not affected by weather (humidity or air temperature). It is not affected by location unless your change of location involves a change in altitude which accompanying pressure change.

Air pressure changes with weather. It's easily visible in old school barometers like http://www.4physics.com/phy_demo/pressure/baro_exp1.jpg

It varies in a range of about +5% to -5% of average pressure.

Which was known about at the time. The ideal gas law for example dates back to 1834 or 27 years before the oldest measurements in this dataset. But even that was not needed with Barometer’s dating back to 1643 and vacuum pumps originating in 1650 allowed for pressure calibration making the current weather unimportant.

Anyway, I think people are vastly underestimating just how far scientists where calibrating things back then. Clock making for example cares deeply about the current temperature.

>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.

One additional caveat specific to ocean (or other large scale systems) property measurement is that, because of the scale, your data can be easily biased because your sensors are not uniformly or even globally deployed. That's increasingly less of a problem in earth science but for geologic data, both in time and space, we are quite liberal in interpolating/extrapolating based on very impactful and sometimes shakey assumptions. This is dangerous because it is very easy for bias from dogma to sneak in unintentionally and undetectably to produce results which may be far removed from truth.

also because sensor deployment density per region varies in time, so measurements across time aren't readily comparable

They do a few checks for this in the article. For example, one of their subsamples is Union Army veterans, and they detect the same trend within those cohorts (0.03 C lower per decade), which used the same instrumentation, as when comparing across the subsamples (e.g., Union Army vs today).

I don't think there is any claim that the same instrumentation is used for the Union Army cohort -- even basic details like whether the temperature is taken orally or axially: "Whether the temperatures were taken orally or in the axilla is unknown; both methods were employed in the 19th century although oral temperature was more common".

That's true, but they do make the more abstract assumption that any bias isn't associated with birth date within cohort. I think the idea is that if there were bias due to instrumentation, it would have to be somehow systematically related to birth date within the cohort.

This is possible if there were some systematic shift in instrumentation with measurement year, but it would be blunted by the extent to which different ages were being sampled at each year.

I agree though that it would be nice to have some information on instrumentation over time and how it relates to temperature measurement.

It's worth noting that the results have practical implications regardless of the explanation of the observed trends, though, which is it's commonly assumed normal body temperature has certain characteristics, without recognizing that that might have shifted in significant ways over time.

It's interesting to me personally because I've often observed my body temp when I'm feeling fine is usually just above 36 C. That doesn't sound like much but it becomes a bigger deal when deciding whether or not I have a significant fever. Some of that might just be individual variation, but this is suggesting there's cohort trends within that too.

They mention that by data analysis they can detect higher temperatures later in the day, varying by 0.02 or 0.01 C in two of their three data sets and this was an expected effect. My intuition would be if the data is good enough to detect small patterns you expect, that is an indication it is reliable enough when telling you about unexpected patterns.

https://en.m.wikipedia.org/wiki/Accuracy_and_precision

You can have a very precise thermometer (repeated measures are tightly clustered) that isn’t accurate (deviates from true value).

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).

> 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).

> 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.

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.

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

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?

> 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.

2 years for 40% reduction in daily calories? No fucking thank you.

You know what blows away the actuarial tables for life expectancy? Exercise. That makes your life better for longer, much more than starving yourself.

I wonder how much of that is driven by suicide. Older men commit suicide at much higher rates than older women:

https://en.wikipedia.org/wiki/Epidemiology_of_suicide#/media...

> I've never seen anything testing that hypothesis.

Actuarial tables would tell you.

Though there would also be confounding variables e.g. previous "at risk" behaviour could still be in effect.

"but women's superior life expectancy seems soley due to high risk behavior by men when they are young and middle age"

huh?

Work, motorcycles, sports, car accidents, ...

>women have been doing it for superficial reasons

could you list those reasons for us?

Don’t know why this is getting downvoted. The parent statement is news to me and I would definitely like to see some sources.

not because of the inquiry itself, wich seems valid, but because the way it's posed, which suggests it's just a bait for grandstanding

it's pretty obvious it's the hackernews patriarchal bubble. men seem to think they know everything about women, and anyone questioning that is put in their place.

FWIW, I would be interested in hearing why you disagree. I think some of the downvotes probably came because the reasons behind the original statement seem very obvious (there is and has been a lot of social pressure on women to look thin; appearance is commonly referred to as a 'superficial' characteristic), so asking for a list instead of just responding to the obvious interpretation can come across as disingenuous.

I don't think asking for clarification on an ambiguous statement is disingenuous, but I'm willing to listen to why you think that.

I said it can come across as disingenuous, largely because the original statement didn't seem ambiguous to me, nor I suspect to the people who downvoted you. And sometimes people pretend not to have understood something, as a way to indirectly criticize it without having to get specific or engage directly. The topic being potentially a controversial one (relating to gender), it seemed like you might have been hinting that the statement was sexist without actually saying why. But I don't know what your actual intent was. (And I'm still not sure whether you have a disagreement with the main substance, i.e. you doubt there would be a relevant difference in prevalence of calorie restriction in men and women, or you think the use of 'superficial' was disrespectful, or something else.)

> 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!

It would also depend whether your skinnyness is metabolic or nutritional (aka do you eat a lot and burn it easily, or eat little / low-calorie stuff).

But fit people live longer, and high intensity exercise seems to increase DNA repair and antioxidants (the high oxidation of exercise seems to be managed by antioxidant processes kicking into gear, which overcompensate for oxidation versus a sessile person from what I've read... casually)

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).

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.

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.

As a child (Italy) I was taught that the temperature measured outside the body (armpit) would be usually 0.5C lower than the one measure inside the body (rectum, mouth).

The threshold for "fever" as reported on all old mercury-based thermometers was exactly 37C and that was referring to the "inside" termperature.

So 36.6 outside would definitely be considered onset of mild fever, not normal. 36.6 inside would be a-ok

Yes, this is how we do it in the US as well: from under the armpit, add 1 degree (F) to get the true temperature, which should be about 98.6

They say this is how 37°C was established:

> In 1851, the German physician Carl Reinhold August Wunderlich obtained millions of axillary temperatures from 25,000 patients in Leipzig, thereby establishing the standard for normal human body temperature of 37°C or 98.6 °F (range: 36.2–37.5°C [97.2- 99.5 °F]) (Mackowiak, 1997; Wunderlich and Sequin, 1871).

The adjective "axillary" means "relating to the armpit", so armpit vs. oral doesn't explain it.

Presumably many patients have abnormal temperatures, so to figure out the normal temperature from patient data would require some kind of filtering.

A couple ways to do that come to mind. One would be to only use patients who are there for things like an annual checkup.

Another way would be to include everyone and then do a graph of x = temperature, y = number of patients with that temperature. I'd expect there to be a peak centered at normal temperature, and another peak at whatever the average fever temperature is.

If whatever method he used was not able to exclude from the "normal" group people who are just starting to get sick and are at the stage where their temperature has started to rise but they are not aware that they are getting sick, he'd get a slightly too high result.

36.6°C is the more modern number:

> A compilation of 27 modern studies, however (Sund-Levander et al., 2002), reported mean temperature to be uniformly lower than Wunderlich’s estimate. Recently, an analysis of more than 35,000 British patients with almost 250,000 temperature measurements, found mean oral temperature to be 36.6°C, confirming this lower value (Obermeyer et al., 2017).

That would make sense, though, if the article is right. A 37C average in ~1850 could be expected to decrease to about 36.5C in the span of 150 years.

98°F is a common reference, and that is about 36.6°C. 98.6°F is a more precise (not necessarily accurate - I don't know either way) measurement that I hear, and that's exactly 37°F.

I wouldn't be surprised if 36.6 is correct, people rounded that up to 37, converted to Fahrenheit, and we just converted back to Celsius.

98.6°F is an over-precise conversion of 37°C. The number was originally measured as 37°C, with two digits of precision. It shouldn't have been reported as 98.6°F, though a correct rounding would have been even less accurate: the number is closer to 98.2°F/36.8°C, but the proper rounding of the conversion would have rounded up to 99°F.

There is, of course, significant variation from person to person, so two digits of precision is probably all that's really appropriate.

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.

> 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.

Nurses are often surprised when they come across someone with an unusual baseline.

Several times after measuring my father’s resting heart rate at <40/minute, a nurse has gone to fetch a doctor out of fear he might have some serious health problem

Yeah. Same in Poland. 36.6C is normal, 37C would be a cause for mild concern.

The temperature also varies during the day by about 0.5 deg.

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

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?

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

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.

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 .

Why do you say that's pseudoscience?

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

https://www.ncbi.nlm.nih.gov/pubmed/29237616

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...

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

Good to know

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

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.

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.

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.

The discussion suggests heating and air conditioning as partial causes. It also discusses reduced infection (which is correlated with lifespan) as time passed due to antibiotics and anti-inflamatories drugs.

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.

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.

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.

This makes a lot of sense to me.

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.

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.

What if overweight people run cooler as well?

In Soviet Union it has always been 36.6

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.

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://uk.reuters.com/article/health-testosterone-levels-dc...

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.

You might know this but be aware that lab testing companies have lowered the acceptable range of testosterone from 348-1197 ng/dL to 264-916 ng/dL, a ~25% decrease. Source: https://www.labcorp.com/assets/11476

Hormone levels fluctuate significantly from day to day based on a variety of factors so a single snapshot testosterone level test doesn't really tell you anything useful (unless it's way outside the reference range). If you suspect a deficiency then you'll need multiple tests over weeks taken at different times of the day in order to get a reliable diagnosis.

Yeah I'm aware. Didn't suspect anything wrong, just wanted to get a baseline established while I'm young

Right, and even then, different doctors/specialties have different standards for what counts as low testosterone. My primary swore up and down that my 300 was fine (and even 200 would be) but men's clinics would insist I need to be at 900.

I'm not sure I'd agree with the men's clinics that will probably more easily sell you appointments for test. prescriptions, but on the other hand LabCorp recently lowered their average range because of the declining measures in the population: https://www.labcorp.com/assets/11476

I think assuming this is the new norm for humans is a mistake, and should instead be treated as a widespread health issue.

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

Only slightly increased risk in the first two years

https://www.webmd.com/heart-disease/news/20190723/testostero...

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

https://en.wikipedia.org/wiki/Androgen_replacement_therapy#A...

There are also lots of conflicting studies like this: https://www.ncbi.nlm.nih.gov/m/pubmed/26248567/

> the only real fix is

What an irresponsible statement. Science has not yet exhausted the frontiers of biomechanics.

No reason to test for a condition now for a future better fix. Test in the future.

Curious if anyone can cite any equivalent research for women, or if it exists?

Girls are hitting puberty earlier and earlier, the average is no 10 years old, whereas it was 15 last century, and significant percents (differs by race though) are hitting it at 7.

Its true with boys to some extent as well according to studies. So at lease for boys/men, there is early onset of hormone production but an overall decrease in the hormone production.

That's not equivalent - indeed, it's not research. Who has measured girls' hormones over time?

High Quality Organic Milk delayed/postponed this for two years (11-13) in our household. Just one datapoint, but we did it on advice from others. We switched from generic milk upon the first indications/hints.

Very interesting, thanks for sharing

Genuinely, I have no idea what you're trying to say. Without scientific sources "high quality organic milk does x" might as well say snake oil. Unless I'm misreading your post, and you're not espousing snake oil.

If I had to guess...I think he is suggesting the added hormones in food (dairy/milk specifically) have a link to early onset of puberty.

It is my understanding both the hormones and antibiotics given to livestock do it fact have impact on the people that consume them.

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> The phytoestrogen stuff that is popping up in other comments than your own seems a lot of BS, honestly

It's hilarious that "soy boy theory" gets parroted so loudly on HN.

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Please stop.

Caring about men's issues is literally an insult. I don't know why you'd think society would give a rip.

It'd actually be quite reassuring if a lot of this was due to body temperature, and not phytoestrogens.

phytoestrogens suppress natural estrogen production because they partially bind to existing estrogen receptors. there was never any (serious) doubt that there was an issue

There's some serious doubt on Wikipedia FWIW... https://en.wikipedia.org/wiki/Phytoestrogen#Males

It is unclear if phytoestrogens have any effect on male sexuality, with conflicting results about the potential effects of isoflavones originating from soy. A 2010 meta-analysis of fifteen placebo-controlled studies said that "neither soy foods nor isoflavone supplements alter measures of bioavailable testosterone concentrations in men."[31] Some studies showed that isoflavone supplementation had no effect on sperm concentration, count, or motility, and had no effects on testicular or ejaculate volume.[32][33] Sperm count decline and increasing rate of testicular cancers in the West may be linked to a higher presence of isoflavone phytoestrogens in the diet, but such a link has not been definitively proven.[34] Furthermore, there is some evidence that phytoestrogens may affect male fertility, but "further investigation is needed before a firm conclusion can be drawn"

Hi, human endocrine researcher here: Wikipedia is garbage for "controversial" medical topics -- it's even worse for many non-controversial biochemical processes (please take a look at the human alcohol metabolism graph... utter garbage!). Citing a few researcher's conclusions (NO! You do NOT do this!) is haphazard, it usually does NOT match the same conclusions one's peers would reach were they to review piece as a whole.

Here's what easily deductively reproduceable with a cursory understanding of the systems involved (and digging through a lot of literature):

> Phytoestrogens bind to estrogen receptors (YES)

> Chemicals -- other than estrogens -- that bind to estrogen receptors are Selective Estrogen Receptor Modulators

> SERMs are NOT the same as estrogens, but they do increase certain estrogenic effects depending on their chemical structure (good: lipid profile, prostate stability; AND bad gynocomastia, electrolyte retention)

> Each SERM has a specific amount of "power" (receptor affinity and corresponding gene expression, i.e how much it increases or decreases the expression of certain genes)

> Soy, and plant products, contain many different phytoestrogens/SERMs, isoflavones are the strongest

Now, onto the goodies:

> The HPTA (Hpyothalmic-Pituitary-Testicular Axis) controls hormone output

> There are estrogen receptors (and others) in the hypothalmus

> Suffice to say, Hypothalmic Hormonal receptors modulate the levels of circulating sex hormones in the body

> When there is an increase of hormones in the body, the excess get bound to hypothalmic receptors, causing the hypothalmus to tell the Pitutary + Testes to produce less hormones OVERALL (FSH, LH, tesosterone, estrogen, etc.)

> Less production of hormones is NOT necessarily bad - Estrogen is the most important hormone in women AND men (take a large amount of any aromatase inhibitor, i.e estrogen "killer," and you will feel a LOT worse than if you were to take an anti-androgen)

> SERMs do decrease circulating hormone levels (by how much is dependent on many variables), due to negative feedback on the HPTA > Once again, this is NOT necessarily bad, because SERMs still bind to estrogen receptors and elicit estrogenic effects on the body

A few for the road:

> Healthy estrogen levels are vital to male libido (as is a proper estrogen:testosterone ratio, too little of either is bad)

> Too little testosterone may also cause too little estrogen, because estrogen is produced in the male body primarily from aromatase (enzyme that converts testosterone to estrogen)

> FSH is involved in sperm production

> LH is involved in testosterone production

This is all the information you need to make an informed opinion on the whole topic. I'm sick of all sides involved. Pseudoscience and agenads, all of you!

Thank you so much for your answer! It's sad how hard it is to get this kind of expert opinion, in the age of information. Do you have any site to recommend over Wikipedia?

Go straight to the source: libgen.lc + https://www.ncbi.nlm.nih.gov/

Having a truly informed opinion is difficult. In the realm of biology, it requires knowing a lot of vocabulary and fundamental systems. However, once that foundation is built, it becomes very easy to educate oneself on any topic within that sphere.

Textbooks are the gold standard -- if you have the time and inclination.

Papers are good for understanding the mechanisms behind why something happens -- but should be taken with a grain of salt.

What conclusions would you draw from this collection of facts?

If I was shooting for complete 100% accuracy:

> "Phytoestrogens, through their ability to bind to all human steroid hormone receptors, exert effects on the miriad of human biological systems that rely on hormones for homeostasis, both directly through SERM-like activity, and indirectly through HPTA modulation of hypothalamic hormone receptors."

If one were to ask "do phytoestrogens impact male: sexuality, sperm count, mood, etc." the answer is always going to by "yes," but it's a misleading yes. We don't get any specificity as to how much of an impact (certain) phytoestrogens have (that is a matter for you to make your mind up on by reading through hundreds of experimental papers and deciding which ones are worth anything ;).

Whatever other questions that stem from this start getting into the realm of public policy and personal impact, "are phytoestrogens bad? Should they be regulated? Am I going to avoid phytoestrogens?" Frankly I have no interest in getting involved in such a subjective matter.

Bulls are also having fertility issue. Climate change is making progress in taming population issues.

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.

They controlled for height and weight in the study

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.

The article posits factors such as:

- reduced inflammation due to improvements in diet and health

- reduced incidence of diseases like tuberculosis

- reduced exposure to ambient temperature extremes

It doesn't mention alcohol, but alcohol consumption can increase inflammation, IIRC.

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.

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.

I thought that was because it slightly increases blood flow - your core temperature drops because your limbs actually are warmed up a bit.

If you drink enough to affect your hypothalamus and raise your body temperature, you're affecting other parts of the brain as well, and in ways that might not be apparent until they become permanent. You should get off of it before it gets any worse.

Do you have any sources backing that? Last time I checked alcohol dilates blood vessel which actually makes you lose heat more easily (but that's just while you're under the influence)

How do you think a thermometer works? You expect it will measure less heat because your vascular system is dilated and shedding more heat?

Core body temp != single point-in-time measurement.

> Core body temp != single point-in-time measurement.

Since when ? Core body temp means exactly what it describes: your internal body temp, you can make it a one time measurement, an average or whatever you want.

> You expect it will measure less heat because your vascular system is dilated and shedding more heat?

I expect that shedding more heat will make your body lose more heat, which will lower your body temperature. I don't even know why it's so controversial in this thread, literally no one is refuting the fact that alcohol increase heat loss.

Lose heat… into a thermometer? :)

Dilated vessel -> more blood to skin -> increased exchange rate with air.

Especially true in cold weather because your body naturally contracts blood vessels to reduce heat transfer, which alcohol completely cancel.

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

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

They addressed this and suggest precision is not the problem.

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