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Is our mean body temperature decreasing and why? What can we learn from it?

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JK
Juran K. Nov 11, 2020

[1]https://www.sciencedaily.com/releases/2020/10/201028171432.htm

[2]https://en.wikipedia.org/wiki/Human_body_temperature

[3]https://advances.sciencemag.org/content/6/44/eabc6599

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Creative contributions

Problems with Carl Wunderlich's temperature measurements

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Shubhankar Kulkarni
Shubhankar Kulkarni Nov 12, 2020

[1]Mackowiak PA, Wasserman SS, Levine MM. A Critical Appraisal of 98.6°F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich. JAMA. 1992;268(12):1578–1580. doi:10.1001/jama.1992.03490120092034 https://jamanetwork.com/journals/jama/article-abstract/400116

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JK
Juran K.2 months ago
I agree. Carl wunderlich also stated that he had a sample of 1 million adults. We definitely need to be careful.
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Povilas S
Povilas S20 days ago
😁

Not global warming

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Shubhankar Kulkarni
Shubhankar Kulkarni Nov 12, 2020

[1]https://www.jci.org/articles/view/135006

[2]https://theconversation.com/how-rising-temperatures-affect-our-health-123016

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Povilas S
Povilas S20 days ago
"It is easier for the body to store the heat (when the ambient temperature is higher)" - what would be the mechanism of the body for doing this?
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Shubhankar Kulkarni
Shubhankar Kulkarni19 days ago
Povilas S
1. "Heat is stored in body fluids, muscles and bones, resulting in an increase in the core temperature."
2. Heat shock proteins are activated to protect enzyme systems and prevent cellular death. These proteins enable excess heat to be stored temporarily. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4515708/)
Another interesting study shows heat stored in muscles during exercise (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2269891/).
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JK
Juran K.2 months ago
Thank you for the contribution! I was thinking about this one, too, but I couldn't find something interesting.
For me, it also makes sense that the body temperature decreasing could be a potentially good strategy against global warming, but I didn't see any signs of this happening. I guess there really is something with much bigger effect that causes the drop.

I don't think its population getting older

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Shubhankar Kulkarni
Shubhankar Kulkarni Nov 12, 2020

[1]https://ourworldindata.org/grapher/age-dependency-breakdown

[2]https://ourworldindata.org/world-population-growth

[3]https://www.prb.org/2020-world-population-data-sheet/#:~:text=The%20world%20population%20is%20projected,as%20in%20the%20United%20States.

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JK
Juran K.2 months ago
I am impressed by the way how you solve problems! The data you extrapolated really says that older population temperature could not be responsible for the drop. I guess it could play a small part in it, but can't fully address it.

What could affect your extrapolated data is the fact that 65 years of age in 1861 was different from being 65 years old today. Since people's lifespan prolonged in this period, maybe being 65 then is more similar to today's 75/80.
But even if we adjust the data (e.g. that today's 65 is 45 in 1861), I think the rate of change would still not be big enough to independently address the problem.

Maybe the hypothalamus?

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Martina Pesce
Martina Pesce Nov 13, 2020

[1][1] D. Grimaldi et al., “Evidence of a diurnal thermogenic handicap in obesity,” Chronobiol. Int., 2015.

[2][1] F. Bastardot, P. Marques-Vidal, and P. Vollenweider, “Association of body temperature with obesity. The CoLaus study,” Int. J. Obes., 2019.

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JK
Juran K.2 months ago
Thank you Martina Pesce on your contributions! This could be on track of something very specific and easier to check, not only statistically, but also experimentally. I like the second paper you referenced. It's simple and clear.

But what they state is that body temperature is positively associated with obesity markers in men and postmenopausal women, what is different from our theory in the beginning of the session. That would mean that our temperature is decreasing because we are getting more fit.

But they also state some other interesting viewpoints that could help us:
- the increase body area of obese subjects does not influence significantly their temperature,
- adipose tissue is secreting hormones (leptin, adiponectin, and cytokines) that could affect other systems like cardiovascular and increase the temperature
- they suspect on indirect relationship between intestinal microbiota composition and thermal homeostasis in humans
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Martina Pesce
Martina Pesce2 months ago
Juran K.
the temperature is positively correlated in the second paper, yes, but in many more was the opposite. I also like more the clarity of the last one.


So, considering that the theme is discussed and sustained in both the opposites directions, it may actually not be the best indicator for our investigation.
This actually sounds to me familiar and typical for obesity-related topics.
It's a very complex phenomenon influenced by many different factors that itself influence many other factors.
edit: just after this I found that somehow obesity is side correlated, for that check my contribution "Great for the lifespan"

Progressive increase in global iron deficiency

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Brett M.
Brett M. Jan 19, 2021

[1]https://www.who.int/vmnis/anaemia/prevalence/summary/anaemia_data_status_t2/en/

[2]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5112924/

[3]https://www.nature.com/articles/pr19871174.pdf?origin=ppub

[4]https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6531837/

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Shubhankar Kulkarni
Shubhankar Kulkarni3 days ago
An interesting finding, Brett M. I am taking a different approach to confirm whether low iron levels can lead to a decrease in the global average body temperature. I want to sort this out mathematically. From the measurements displayed in the session text, we know that the average human body temperature is/ was 37 deg. C and we know that the current average is 36.39 deg. C. If 75% of the population (having normal iron levels) has a body temperature of 37 deg. C. and if the remaining 25% (having reduced iron levels/ anemic individuals) has a body temperature of X deg. C., (75*37 + 25*X)/100 should equal to 36.39 deg. C. Using this equation, the value to X is 34.56 deg. C.

A body temperature of 34 deg. C. is not impossible and it is a classic sign of hypothermia. However, I could not find the absolute decrease in the body temperature caused by iron deficiency in humans. If there are reports that anemic individuals present a body temperature of 34 deg. C. or lower, we might be able to prove the point.

Furthermore, I am not sure whether all forms of anemia cause a decrease in the body temperature but, in this regard, about 47% of the urban Indians have vitamin 12 deficiency, [1] which can also lead to anemia (Pernicious anemia). 47% is a sufficient proportion to cause a nation-wide decrease in the average body temperature. However, again, I could not find the net decrease in the body temperature caused by anemia.

Here is another study that concludes that a transition from the nomadic hunter-gatherer to the urbanized and sedentary lifestyle has increased the prevalence of anemia. The authors also mention that the diet of the studied people (Kalahari community in Africa) did not change with the transition and, hence, the drop in the iron levels cannot be attributed to diet. [2]

Reference:
1. Singla R, Garg A, Surana V, Aggarwal S, Gupta G, Singla S. Vitamin B12 Deficiency is Endemic in Indian Population: A Perspective from North India. Indian J Endocrinol Metab. 2019;23(2):211-214. doi:10.4103/ijem.IJEM_122_19
2. Kent S, Dunn D. Anemia and the transition of nomadic hunter-gatherers to a sedentary life-style: follow-up study of a Kalahari community. Am J Phys Anthropol. 1996 Mar;99(3):455-72. doi: 10.1002/(SICI)1096-8644(199603)99:3<455::AID-AJPA7>3.0.CO;2-V. PMID: 8850185.
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JK
Juran K.3 days ago
Nice correlation data. I would agree that the correlation between iron and thermogenesis exists. Many sources confirm that low body temperature (BT) is one of the symptoms of low blood iron [1, 2].

Few things I would like to check before concluding anything.
The first one is the statistics of anemia from 2016 compared to 2011-2012, 2003-2004, and 1993-2005. Many historical measurements in medicine are significantly lower because of the increase in the number of BT measurements as a standard procedure (statistically more anemic persons will be measured and reported). Also, technology is becoming more and more sensitive and thus, more patients emerge every day.

The second thing that concerns me is the fact that in human experiments, they mostly correlated iron-deficiency and like you said, "a blunted thermogenic response when exposed to cold temperatures", but there were no data on the effect of iron deficiency on the BT when in normal conditions. Based on experiments on mice, scientists try to explain it like this:
Two possible mechanisms of how iron deficiency could affect thermogenesis are i) anemia and ii) the other involving tissue iron deficiency [3]. Iron-deficiency anemia results in decreased blood oxygen transport, which reduces the physiological response of the body temperature to cold. Low oxygen contents can result in hypoxia and further, hypothermia. The other mechanism involving tissue-iron deficiency accounts for the decreased activity of mitochondrial iron-containing enzymes that produce ATP, which reflects in, again, worse muscle response to cold.

Taking both mechanisms into account, I found strong evidence that the iron-deficiency affects the thermoregulation in cold, but not so significant in normal conditions (correct me if I am wrong). Believing that the conditions in the laboratory where the temperature was measured in previously mentioned papers [4] are normal, I am not so sure to what extent could the rate of anemia affect the observed reduction in BT. If we also take into account the Povilas S´s comment on likeliness, I think we need more research and statistics on this.

References:
1 https://consumer.healthday.com/circulatory-system-information-7/anemia-news-25/health-tip-symptoms-of-iron-deficiency-anemia-730529.html
2 https://www.medicinenet.com/iron_deficiency_symptoms_and_signs/symptoms.htm
3 https://www.nap.edu/read/5197/chapter/19#248
4 https://www.sciencedaily.com/releases/2020/10/201028171432.htm
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Povilas S
Povilas S4 days ago
Interesting find. Did you get to know the reasons why anemia is increasingly more prevalent?

One objection to this would be that even though anemic people comprise quite a large part of the general population (~25% as you note) the observed general BT (body temperature) decrease trend can't be solely because of them, because studies dealing with BT measurements would then identify BT decrease only as prevailing in certain subjects. In other words, for studies claiming the general trend of BT decrease to be statistically sound, BT decrease has to be more or less evenly distributed among subjects, if 75 percent had the decrease and 25 not, then maybe it could count, but not the other way around. Otherwise, this would be an error-based conclusion. It's highly unlikely that BT studies somehow included the majority of anemic people in their subject samples. This could be a supplementary cause though.

A bit of everything

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Martina Pesce
Martina Pesce Nov 13, 2020
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Shubhankar Kulkarni
Shubhankar Kulkarni2 months ago
Martina Pesce I had the same thought. You beat me to it. :)
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JK
Juran K.2 months ago
I agree with you. Maybe I can do an updating list of proposed "maybe's and maybe-not's" on the bottom of session description, so that every newcomer has an overall picture what has been proposed or not.

Other environmental factors (if not global warming)

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Povilas S
Povilas S Jan 05, 2021
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Darko Savic
Darko Savic6 days ago
If the rise of atmospheric CO2 is the cause, then many animal species should be affected as well. How is the body temperature of wild animals or a domesticated species that lives outdoors? Even cattle results would be viable.

In which situations is the body temperature of animals taken/logged on a regular basis, over years? Expensive racehorses, various famous endangered animals that are being tracked, etc.

How are sea animals doing? Dolphins? Whales? Do any of them have permanent monitoring devices that also report the body temperature?
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Shubhankar Kulkarni
Shubhankar Kulkarni11 days ago
Povilas S CO2 concentrations stood out when I read this. So I did some research and found that it might be true - an increase in the ambient CO2 concentration may decrease core body temperature. Here is an amazing paper (https://journals.physiology.org/doi/full/10.1152/japplphysiol.00010.2010) that demonstrates it (please look at Figure 1A). They made their participants exercise (cardio) for 60 minutes with and without CO2-enriched ambient air and monitored their core temperature (oesophageal temperature), blood pressure, and heart rate throughout. They found that although the blood pressure and the heart rate did not change, the rise in body temperature due to exercise was lower in the CO2-enriched air and the normal air.

Moreover, according to another paper, the solubility constant of CO2 in the blood depends on body temperature. The rise in body temperature decreases the solubility constant. Therefore, probably, to accommodate the increased CO2 from the ambient air in the blood, the temperature of the blood decreases. (https://www.jbc.org/content/44/1/131.full.pdf)

Also, the global average atmospheric carbon dioxide was the highest in 2019 (409.8 parts per million). Carbon dioxide levels then were higher than at any point in at least the last 800,000 years. (https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide#:~:text=Global%20atmospheric%20carbon%20dioxide%20was,%C2%B1%200.1%20ppm%20per%20year.) Therefore, even if certain geographical areas have a higher CO2 concentration than others, the difference is insignificant compared to the increase in the global average over time.

However, there is a small twist in this. Although the body temperature decreases to accommodate more CO2, it also decreases to compensate for the decreased oxygen levels in the atmosphere. There are two ways in which the body compensates for oxygen deficiency -
1. By increasing respiration (inhalation of O2) and by increasing the solubility of O2 in the blood.
2. Lowering oxygen demands by the body by decreasing the body temperature. (https://journals.physiology.org/doi/abs/10.1152/ajplegacy.1937.120.1.190?journalCode=ajplegacy) It was shown that mice exposed to air containing 8.1% oxygen showed a drop in their body temperature by about 2.5 to 3 deg C. Also, if CO2 is increased by 3%, the body temperature decreases further. Also, if the room temperature is elevated to 35 deg. C., the mice died when exposed to an oxygen pressure, which they could tolerate at normal room temperature (probably 25 deg. C.). To drive the point further, here is a reference that shows the fall in atmospheric O2 content over the years. (https://www.oxygenlevels.org/)

Taken together, these studies demonstrate that decrease in atmospheric O2 and an increase in atmospheric CO2 cause a fall in body temperature. As these conditions are currently observed at the global level, the global fall in the body temperature could be attributed to these.
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JK
Juran K.16 days ago
First, thank you Povilas S for the contribution!

I agree that the causing factor of the lower BT is probably something very similar to both observed populations and I can understand the reasons why you think there is only a small number of probable factors. I would not say that global warming was ruled out - just left out of the supporting arguments. But here you mention global environmental changes. They are not ruled out and are not a small number of factors. Global environmental changes range from lifestyle changes, animal interactions to devastating natural disasters and are the consequence of artificial (human) or natural processes - thus, high on our list. :)

I am not sure I understand what is your point in the third paragraph. In this paper, we follow an approximately two-decade-long socioeconomic change that was correlated with a significant BT drop. The socioeconomic change that was observed amongst the Tsimane people was pretty drastic and it could potentially reflect the proportionally drastic BT drop.
Also, let's say that human-caused climate change becomes evident around the 1980s. That means we have a period of 20 years with no data before the BT change was observed and tracked - true.
But, what would you do with the info if you knew that the temperature was decreasing at the same rate in the period from the 1980s to 2002? How would this data help us in determining the main factors that caused BT to drop? Can you tell me what you aim for?

You had some really interesting statements In the last paragraph! It could be true that people who are "deeper immersed into nature", better reflect the environmental changes than those lying in their air-conditioned offices and homes. I love the new perspective of circularity you give here - changing people cause the change in people. Nature could just be the boomerang that serves as a medium and a partial absorber of the returning change.

How about prostaglandins and IUD?

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Martina Pesce
Martina Pesce Nov 13, 2020

[1] "Eicosanoid Synthesis and Metabolism: Prostaglandins, Thromboxanes, Leukotrienes, Lipoxins". themedicalbiochemistrypage.org. Retrieved 2018-09-21.

[2] Mary Anne Koda-Kimble (2007). Handbook of Applied Therapeutics (8th ed.). Lippincott Williams & Wilkins. p. 1104. ISBN 9780781790260.

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Shubhankar Kulkarni
Shubhankar Kulkarni2 months ago
Juran K. Only 10% of the women in the United States use intrauterine devices (https://www.cdc.gov/nchs/fastats/contraceptive.htm). Martina Pesce How do the IUDs affect body temperature - positively or negatively?
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Martina Pesce
Martina Pesce2 months ago
Shubhankar Kulkarni
UPS! I must have got confused: IUD increases the productions of prostaglandins, which increases the temperature. So, actually...not the IUD.
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JK
Juran K.2 months ago
Nice! I didn't remember to look at the problem from that perspective. It could be useful to look for inner regulators of body temperature and what affects them.

Also, since 49.584% of the world population are women (https://data.worldbank.org/indicator/SP.POP.TOTL.FE.ZS), the intrauterine device could affect the temperature on a larger scale. But we first need the data on how many females actually use those.

Reduced number of infections or physical activity

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Shubhankar Kulkarni
Shubhankar Kulkarni Nov 24, 2020

[1]https://jamanetwork.com/journals/jama/fullarticle/768249

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JK
Juran K.2 months ago
I understand the model you propose and yes, it could explain the observation of slightly reduced body temperature. It fits in "a bit of everything" theory.

But the problem with this is that the measurements are usually done at the hospital, in one moment, on one, usually sick individual, once. Statistically, it could be possible that the sample is nonbiased, but then the patients at the regular examination need to be taken into account, too. What they did in the study I mentioned in the session description is that they adjusted the data to the patient diagnosis (infections, general state) and didn't find a pattern.

Concerning physical activity, it is not very likely that someone will do a hardcore physical activity and then go to an examination or measure the body temperature and report it to a doctor. I don't know how we could fit that into the adjustment algorithm, but it could definitely contribute.
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Shubhankar Kulkarni
Shubhankar Kulkarni2 months ago
Juran K. I agree with your comment concerning the effect of decreased infections on average body temperature.

Regarding physical activity, although it is unlikely that the participant had a run and then visited the clinic, the regular commute would be involving more physical activity then. For example, the participant would be more like to ride a cycle and climb up the floor to the clinic than travel in a car and use the lift. Since the year of the initial measurement is 1861, we cannot eliminate this possibility.
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JK
Juran K.2 months ago
Shubhankar Kulkarni I agree, it should be taken into account.

Ambient temperature in the clinic might explain the differences in the average body temperature

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Shubhankar Kulkarni
Shubhankar Kulkarni Nov 26, 2020

[1]Mackowiak PA, Wasserman SS, Levine MM. A Critical Appraisal of 98.6°F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich. JAMA. 1992;268(12):1578–1580. doi:10.1001/jama.1992.03490120092034 https://jamanetwork.com/journals/jama/article-abstract/400116

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JK
Juran K.2 months ago
This is an excellent find! I really like the simplicity of the study you linked. It could play a role in the mentioned changes in body temperature.

What I find a bit tricky is the sample size (41 participants), but that could be taken as a minor flaw.
Also, as you mentioned, the extreme temperatures seem a bit too radical. Plus, even after these extreme conditions, the temperature seems to get back to normal in the period of 20 mins, especially in females. If we take into account the average temperature differences inside and outside the hospitals and the average waiting time, the effects fall fairly below significant, I think.

What could support this idea is the integration of the thermometers into smartwatches or smartphones to follow the body temperature continuously. Also, the COVID-19 temperature measurement at airports, hospitals, pharmacies, shops, etc. could be used to test the theory.
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Shubhankar Kulkarni
Shubhankar Kulkarni2 months ago
Juran K. Agreed! Even I loved the simplicity of the study, there was no confusion.

Yes, there will be a lot of data with COVID-19 testing that can be put to use for topics other than COVID-19.

Measurements were taken in different climate zones

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Darko Savic
Darko Savic Jan 15, 2021
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JK
Juran K.7 days ago
True, the measurements were done on people in different climate areas.

While researching on this, I found tons of material supporting a theory of the human body being an amazing machine that is capable of coping with different environmental temperatures, just so it's temperature could remain unchanged. Body functions perfectly on let's say, 36.6 degrees Celsius. When we say body, we mean organs and tissues made of cells, which are made of lipids, sugars, and proteins. To "work" on optimal turnover times, synthesize, degrade, or maintain the rate of chemical reactions, the body needs optimal conditions. Any small change in body temperature reflects heavily on cell and tissue mechanisms. That could be the reason why hot-blooded organisms, including humans, should have a constant body temperature. if the protein, sugar, and lipid structure or content are the same in all climate zones, then the body temperature should be, too.

On the other hand, why it could be true that body temperature change according to the climate? The problem is that we do not always measure the "body" temperature, but oral, tympanic, or rectal temperatures, from which the oral and tympanic vary the most. How could they vary? Some findings reported different body temperature measurements after the 15-min exposure to cold or hot temperatures. Shubhankar Kulkarni mentioned it in his contribution above and concluded that even much smaller temperatures could play a role in a temperature change. Therefore, it's not strange to conclude that people living in different climate zone could have slightly different "surface" body temperature - just because of the measurement method.

That could be the reason why your idea could be true (for this study). But are the "real" temperatures of the body changing according to the climate zones? I would say not.
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Povilas S
Povilas S4 days ago
Juran K. , Darko Savic This seems to be already accepted as know phenomenon, it couldn't be just from one study. The one with Tsimane people is another example, are there more?
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Povilas S
Povilas S4 days ago
https://elifesciences.org/articles/49555 It seems that there's enough proof.

Great for the lifespan

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Martina Pesce
Martina Pesce Nov 23, 2020

[1] Conti, B.; Sanchez-Alavez, M.; Winsky-Sommerer, R.; Morale, M. C.; Lucero, J.; Brownell, S.; Fabre, V.; Huitron-Resendiz, S.; Henriksen, S.; Zorrilla, E. P.; De Lecea, L.; Bartfai, T. (2006). "Transgenic Mice with a Reduced Core Body Temperature Have an Increased Life Span". Science. 314 (5800): 825–828.

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Shubhankar Kulkarni
Shubhankar Kulkarni2 months ago
Martina Pesce Great find! The causality you mentioned in your suggestion (lower temperature leads to a higher lifespan) is the opposite of the one mentioned in another suggestion ("I don't think its population getting older") on this session. I think what you have suggested can very well be the (or one of the) reasons for the reduced body temperature. We were looking at it from the perspective of an "effect" but it can also be the "cause" of something. In the paper you cited, the authors report a reduction in the physical activity of the mice, which can also be one of the reasons. We do not know whether the reduction in physical activity was due to genetic modification (Heterozygous Hcrt-UCP2 mice).

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Darko Savic
Darko Savic6 days ago
While this couldn't be the reason, it should be mentioned. Entropy is slowly but persistently decreasing the temperature of everything in the universe. We seem to be on the one-way road to the heat death of the universe https://en.wikipedia.org/wiki/Heat_death_of_the_universe.
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JK
Juran K.5 days ago
Darko Savic Interesting theory. I didn`t hear about it before. That would mean that the temperature of the air, earth, sea, and all the other waters should be decreasing too? I guess the air is heavily influenced by global warming, but the other elements should respond to this, right? In our case, I guess the time frame of 20-30 years is definitely too small to "catch" the difference in temperature caused by the entropy. But if we had a much bigger time frame (since these events such as the Big Freeze are planned to occur in about 10^100 years), we could catch the change caused by the entropy.
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Darko Savic
Darko Savic5 days ago
Juran For us on earth, things will first get much hotter (sun expanding) before they get colder. But eventually, yes - entropy is coming for everything in the universe - https://youtu.be/80tdw-kBiu8