Dyotak Chandra, The West Bengal University Of Health Sciences
Since the past two centuries, 98.6°F (37C) is taken as the standard “normal” body temperature. First established by German physician Carl Wunderlich, it has been used by doctors and parents as a measure by which fever can be assessed and to detect the severity of any infection. Temperature is a vital parameter that helps in the detection of the physiological processes that are taking place inside the body similar to a metabolic thermostat. Body temperature is not uniform for everyone and also not for an individual. Body temperature varies by 1F during the day, being the lowest during the early morning and the highest in the late afternoon. Body temperature also shows certain variations during the menstrual cycle and at the same time, it also decreases with age. Certain research also suggests that body temperature is a marker of life expectancy.
Over time however lower body temperature is being reported in healthy adults. A 2017 study among 35000 adults of the United Kingdom reported an average body temperature of 97.9F. Another study in 2019 on the American population revealed that the average normal body temperature is 97.5F. Similarly, a multinational team of physicians, anthropologists, and researcher-led by Michael Gurven, UC Santa Barbara noted a similar decrease in the normal body temperature among the Tsimane, an indigenous population of forager horticulturists in the Bolivian Amazon. In the Tsimane the body temperature is being seen to rapidly decline at a rate of 0.09F per year, such that at present the Tsimane have a body temperature is about 97.7F.
According to Gurven, the decline in body temperature that occurred in the last two decades is equivalent to that observed in the U.S over approximately two centuries. According to Gurven body temperature in the U.S is seen to decline from the time of the Civil War. One probable cause for this decline can be infections have decreased among people due to improved hygiene, clean water, vaccination, and treatment. While certain infections were associated with higher body temperature, these patients did not show a steep decline in body temperature. But in general, there is a steep decline in the body temperature of so-called healthy individuals.
The answer to why the body temperature is decreasing cannot be justified just by the modern healthcare facilities and lowered infection rate but by a combination of several factors. It could be due to the widespread use of antibiotics which lowers the infection duration or due to the extravagant use of anti-inflammatory drugs like ibuprofen that reduces inflammation. Further, it could also be due to the use of air conditioners in the summer and heaters in the winter that our body does not have to work that hard to regulate the internal body temperature. Moreover, besides the UK and the US temperature decline is also seen in tropical countries where the infection is one of the major causes of mortality. So it is not just one factor but a group of factors which caused the decline in body temperature with few questions still unanswered.
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Source – Michael Gurven, Thomas S. Kraft, Sarah Alami, Juan Copajira Adrian, Edhitt Cortez Linares, Daniel Cummings, Daniel Eid Rodriguez, Paul L. Hooper, Adrian V. Jaeggi, Raul Quispe Gutierrez, Ivan Maldonado Suarez, Edmond Seabright, Hillard Kaplan, Jonathan Stieglitz, Benjamin Trumble. Rapidly declining body temperature in a tropical human population. Science Advances, 2020; 6 (44): eabc6599 DOI: 10.1126/sciadv.abc6599
https://advances.sciencemag.org/content/6/44/eabc6599
The topic is so very relevant ❤️