Human body temperature has decreased in United States, study finds
med.stanford.edu
med.stanford.edu
Let's not ignore the elephant in the room. A sedentary lifestyle with minimal exercise has become the norm.
Given that the people involved are in their 20s I would guess that obesity plays less of a role than you'd expect.
[1]: https://en.wikipedia.org/wiki/Obesity_in_the_United_States#/...
(I would almost expect, that the study authors know of something like that, and would have mentioned it, if it were the case.)
The story of willowfine is roughly as well known as penicillin. The point is that in 1910-1920 people didn't carry NSAIDs in their purse and pop 400 mg when they felt a headache coming on or their back hurt. That's a big difference.
It's also worth noting that right at that point, the supply of aspirin was very limited due to phenol shortages caused by the war.
Human body temperature varies naturally by about 5 degrees F. This study is talking about a .4 degree change. At the very least, your body can definitely handle it. This is purely an interesting phenomenon that may not even be real.
Aspirin is very well-studied and definitely known to be very beneficial for your lifespan and quality of life. You should absolutely not throw away all that knowledge because it may be tangentially related to arbitrary theorizing (about inflammation) on a strange result on sketchy data from uncontrolled groups with unknowable biases. Medicine is proven to be good for you. Even if it does have unknown negative effects -even if this is an effect that we don't know about, that may not even be bad- you should not disregard medical wisdom for the sake of what you don't know.
Relatively speaking, it also has a fair low LD50. For a person around 150lb, 40 standard 325mg pills can be fatal. In fact you'll almost never, outside of hospital supply, find the 81mg chewable version in quantities higher than 36 in case children get a hold and think they're candy. Even then, a 2 year old downing a whole bottle would still be close to an LD50.
All in all, despite being extremely common and cheap to the point of nearly free ($10 for a year's daily supply) it is actually less safe than other NSAID class drugs. But then none of this stuff, strictly speaking, is "safe" if it is used outside of it's normal use parameters.
CO2 levels for example can negatively impact cognitive function [1], perhaps this could have some impact on energy expenditure in the brain which might reduce body temperature some. Bodies will absolutely adjust to temperature changes as well (to some extent). Plausible but probably not a large percentage of a body temperature.
I could see people being exposed to higher CO2 levels though due to the fact there are more and more indoor jobs, and less due to climate change. Even with HVAC systems, a quick Google query makes it seem that CO2 levels are generally higher in offices than outside [2] [3] [4] [5].
And while we're on that brain line of thinking... perhaps the increased consumption of television and mindless scrolling of social media feeds also results in far lower cognitive engagement which also decreases energy expenditure shrugs. Also worth looking at I suspect.
For me I immediately thought of the thermic effect of food. Legumes, many spices, nuts, seeds etc all tend to have higher thermic effects. Perhaps eating a highly refined carbohydrate diet has caused a lowering in body temerapture by having lower thermic effects (I don't know, this was just my first mental leap). I suspect there is something here but probably not a major percentage of the difference.
[1] = https://ehp.niehs.nih.gov/doi/10.1289/ehp.1510037
[2] - https://www.businessinsider.com/office-air-co2-levels-making...
[3] - https://www.ncbi.nlm.nih.gov/pubmed/26273786
[4] - https://www.planteriagroup.com/blog/co2-levels-in-offices-ar...
[5] - https://www.washingtonpost.com/news/energy-environment/wp/20...
More importantly, you can't infer anything about the CO2 levels when they were being measured from the global CO2. Big buildings would have had very high CO2 levels since there's no central air. Small buildings would have much lower CO2 than any current buildings when the windows were open, and much higher otherwise. Oil or gas lamps would raise the CO2 levels a ton. Proximity to coal furnaces would have had a huge impact. Fireplaces too.
Bottom line: global CO2 levels have virtually nothing to do with how much CO2 people are exposed to.
Some of these alternatives, like temporal scan thermometers vary dramatically.
The people being studied were in their 20s- obesity has increased 4-5x among children since 1980, but it's still only 20-25% for people in their 20s. Since then we've gotten gym class and advil- they had barely gotten aspirin.
Selection bias probably plays a very large part. They may have been able to measure temperatures but I doubt they were rigorous about taking representative cross-sections in 1910. Additionally the bias towards obesity has roughly switched- wealthier people were more likely to be obese in the 1900s, and now poorer people are more likely to be obese.
That said, muscle mass correlates almost directly with energy consumption. Muscles literally require energy to stay limp. Rigor mortis is caused by the supply of energy being cut off. The majority of the body's energy requirement is spent just keeping your muscles in working order- not even moving.
That aside, the brain burns a significant percentage of calories burned. Perhaps on whole we are thinking less?
Whatever happen to HN being a space where a legit "what if?" was explored, not knocked?
If you're sitting on your ass all day and then going out to drink a gallon of HFCS-infused coke (free refills) and a low-budget meal that could satisfy a starving family, of course you're gonna get to this point.
My personal thought with the US is "why does everything have to be so big?"
Huh? fitness industry is booming! Gym attendance is near all time highs! More and more people are eating healthier and switch to healthier and more active lifestyle.
The rates of intentional exercise - going to a gym and working out - are certainly on the rise, but the actual rate of exercise is more lower than it was a hundred years ago. The job market has switched in large part to sedentary jobs from active jobs. And diets are much less healthy today than they were then because the only diets available (to anyone other than the rich) were relatively healthy. It’s hard to become overweight without the presence of junk food. Not impossible, certainly, but hard.
I think there were a lot of these little things that mean that yes, our 'sedentary' grandparents and great-grandparents were a lot more active just because of how life was.
Unfortunately, it seems pretty predictable given the changes in our lifestyles...
I'd be careful with that assumption. Context means everything. It depends on what caused the inflammation, and what is causing its decrease.
> Economic development, improved standards of living and sanitation, decreased chronic infections from war injuries, improved dental hygiene, the waning of tuberculosis and malaria infections, and the dawn of the antibiotic age together are likely to have decreased chronic inflammation since the 19th century. For example, in the mid-19th century, 2–3% of the population would have been living with active tuberculosis (Tiemersma et al., 2011). This figure is consistent with the UAVCW Surgeons' Certificates that reported 737 cases of active tuberculosis among 23,757 subjects (3.1%). That UAVCW veterans who reported either current tuberculosis or pneumonia had a higher temperature (0.19°C and 0.03°C respectively) than those without infectious conditions supports this theory.
I would assume that less tuberculosis is a good thing (though, this being Hacker News, someone will probably show up to question that assumption too).
Tuberculosis is a disease, and widely accepted as detrimental to human health. I agree, less tuberculosis = a good thing.
This being a medically related post, more information, and less assumptions is better for everyone. Thank you for adding context.
> Changes in ambient temperature may also explain some of the observed change in body temperature over time. Maintaining constant body temperature despite fluctuations in ambient temperature consumes up to 50–70% of daily energy intake (Levine, 2007).
> Resting metabolic rate (RMR), for which body temperature is a crude proxy, increases when the ambient temperature decreases below or rises above the thermoneutral zone, that is the temperature of the environment at which humans can maintain normal temperature with minimum energy expenditure (Erikson et al., 1956).
> ... Thus, the amount of time the population has spent at thermoneutral zones has markedly increased, potentially causing a decrease in RMR, and, by analogy, body temperature.
Our average lifespan is longer than it used to be. I'd assume older people have a lower base temperature. This would skew the results statistically.
See the numerous studies that cannot be replicated, the below-the-surface iceberg of unpublished (unfavorable) studies paid for by for-profit institutions, or the shockingly small sample set or biased sample set in most studies. Most studies expose this information implicitly but it's up to the reader to determine the bias or replicate the study.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6456186
Axillary (armpit) measurements, for example, are a lot colder than oral or rectal measurements. Perhaps the Russians favoured the former, while the Americans preferred the latter?
I suspect there's a nice little bell curve with 37°C in the middle.
Edit: A 37 temperature would automatically give you an excuse from school when I was a kid and, obviously, children always were finding ways to cheat. If just putting the thermometer in your mouth worked then either I was in the dark or nobody has discovered this.
Isn't it likely that this is just a measurement/calibration/methodology error?
> As part of the study, the authors investigated the possibility that the decrease could simply reflect improvements in thermometer technology; thermometers used today are far more accurate than those used two centuries ago. “In the 19thcentury, thermometry was just beginning,” Parsonnet said.
> To assess whether temperatures truly decreased, the researchers checked for body temperature trends within each dataset; for each historical group, they expected that measurements would be taken with similar thermometers. Within the veterans dataset, they observed a similar decrease for each decade, consistent with observations made using the combined data.
Maybe the original paper discusses the point though? Perhaps they have a way to normalize temperatures to a baseline across all data sets and evaluate that way.
Protsiv, M., Ley, C., Lankester, J., Hastie, T., & Parsonnet, J. (2020). Decreasing human body temperature in the United States since the industrial revolution. eLife, 9, e49555.
When working in offices, I have noticed that people who drink pop/soda daily prefer lower room temperature than people not consuming them at all. I might have "noticed" it because of a bunch of biases, but I'd love to see a proper study on that.
Our main source is fortified salt and everyone is cutting back on their sodium or using fancier salts that don’t add iodine.
I make sure to put a pinch of iodized salt in everything I cook.
Dairy and grain are the biggest sources of iodine. To get your iodine from salt alone would require over 3 grams per day, which is quite a lot. The average American consumes 3.4 g, DV recommendation is 2.3 g.
People also became bigger during the last century which results in better thermodynamics, ie. surface/volume ratio, thus less need for burning of the internal fuel, i.e metabolic rate can be lower. Compare - elephant's 96.6 vs. cat's 101.5 body temp.
Obesity: raises temperature
exercise: lowers resting temperature
junk food: raises temperature
Frankly I’m not buying the arguments in the article. Occam’s razor says it’s a common nutritional deficiency or environmental toxin affecting the thyroid.
After therapy my significant other tells me I’m like a body heater constantly radiating heat possibly due to high synthesis and metabolism.
I’m curious but there was a chart I saw as well regarding men’s testosterone levels declining over the last century I wonder how related that is to lowered body temperatures
However, fevers are caused by a subset of the interleukin family, which as a whole causes inflammation. Inflammation was the author's suggestion.
Also, low grade fevers aren't a thing. Fever is caused by the immune system. You can only have a continuous infection with diseases that avoid or supress the immune system. There are a small number of brain-affecting infectious diseases like meningitis that can raise body temperature on their own. Chronically recurring stuff will also give you intermittent fevers, but there's no low-grade. You have it or you don't.
According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[10] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer's scale, brine freezes at zero, water freezes and melts at 7.5 degrees, body temperature is 22.5, and water boils at 60 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and make the scale more fine-grained. He then re-calibrated his scale using the melting point of ice and normal human body temperature (which were at 30 and 90 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees and body temperature 96 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).
Fahrenheit soon after observed that water boils at about 212 degrees using this scale. The use of the freezing and boiling points of water as thermometer fixed reference points became popular following the work of Anders Celsius and these fixed points were adopted by a committee of the Royal Society led by Henry Cavendish in 1776. Under this system, the Fahrenheit scale is redefined slightly so that the freezing point of water is exactly 32 °F, and the boiling point is exactly 212 °F or 180 degrees higher. It is for this reason that normal human body temperature is approximately 98.2° (sic) on the revised scale (whereas it was 90° on Fahrenheit's multiplication of Rømer, and 96° on his original scale).
https://antoine.frostburg.edu/chem/senese/101/solutions/faq/...
You would expect the opposite of what you're suggesting, if anything. If water was used for calibrating temperature then there would be fewer good ways to control the impurity level, which would lower its freezing point. Not to mention Fahrenheit originally defined body temperature as 96 F, and it was later corrected higher.
All of the above is totally moot because we have plenty of medical thermometers from the 1900s and earlier, and they are remarkably accurate and the error is not particularly biased in either way. This is a highly researched area because the accuracy of whether thermometers is important to historical and climate research. Medical thermometers from the 1800s are good to at least 1/5th of a degree and instrumentation thermometers were good to hundredths.