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Doctors know that there is not one “normal” body temperature for everyone at all times, despite stabilizing at 98.6 ° F (37 ° C).
Throughout the day, your body temperature can fluctuate by around 1 Fahrenheit, with early morning lows and late afternoon highs. It changes when you are sick, increases during and after exercise, varies throughout the menstrual cycle and between individuals, and tends to decrease with age.
In other words, body temperature is an indicator of what’s going on inside your body, like a metabolic thermostat.
And an interesting study, carried out earlier this year, found that normal body temperatures were around 97.5 degrees Fahrenheit among Americans – at least in Palo Alto, Calif., Where researchers carried out hundreds of thousands temperature readings. This indicates that in the United States, normal body temperature has declined over the past 150 years.
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A standard of 98.6 F for “normal body temperature” was first established by German physician Karl Wunderlich in 1867 after studying 25,000 people in Leipzig. However, lower body temperatures have been widely reported in healthy adults. A 2017 study of 35,000 adults in the UK observed an average body temperature of 97.9 degrees Fahrenheit.
What could be causing these subtle and important changes? Are these provocative signals of changes in human physiology only happening in urban and industrial areas, like the US and UK?
One of the main assumptions is that with improved hygiene, sanitation and medical treatment, people today suffer from fewer infections that could lead to an increase in body temperature. The researchers were able to directly test this idea in a unique environment: at the horticulturalists of Tsimane, in the Bolivian Amazon.
The Tsimane lives in a remote area with limited access to modern facilities, and we know from firsthand experience that infections are common – from colds to intestinal worms to tuberculosis. And after the research team worked with Tsimane on a variety of health and aging topics for two decades, they had the opportunity to see if body temperatures drop similarly in this tropical environment, where infection is most common.
As part of the Tsimane Health and Life History project, a mobile team of Bolivian doctors and researchers travel from village to village to monitor health while treating patients. They record clinical diagnoses and laboratory measurements of infection at each patient visit.
When they started working in Bolivia in 2002, the body temperatures of Tsimane individuals were similar to those found in Germany and the United States two centuries ago: on average 98.6 degrees Fahrenheit, but over a relatively short period of time. age 16, they noticed a rapid decline in the average. Body temperature in this community. The drop is steep: 0.09 degrees Fahrenheit per year, temperatures today are hovering around 97.7 degrees Fahrenheit.
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In other words, in less than two decades, we are witnessing the same level of degradation observed in the United States for nearly two centuries. This can be said for sure, as the analysis is based on a large sample (around 18,000 observations for almost 5,500 adults), with statistical control for many other factors that can affect body temperature, such as ambient temperature and mass. bodily.
More importantly, while the incidence of certain illnesses, such as respiratory or skin infections, were associated with a high body temperature during a medical visit, adaptation to this infection did not explain the sharp drop in temperature. body over time.
So why has body temperature dropped over time for both Americans and Tsimane? Fortunately, there is evidence from long-term research in Bolivia to address some of the possibilities.
For example, the decrease may be due to higher modern healthcare and lower rates of persistent mild infections now compared to the past. But although health has generally improved in Bolivia over the past two decades, the infection is still widespread among the Tsimane. The results indicate that the lower incidence of infection alone cannot explain the observed decrease in body temperature.
And people can be in better shape, so their bodies don’t have to work so hard to fight infection. Or, increased access to antibiotics and other treatments means the duration of infection is shorter now than it was in the past. It is also possible that increasing the use of certain medications such as ibuprofen or aspirin may reduce inflammation, which results in lower temperatures. However, while laboratory measurements of system-level inflammation were associated with elevated body temperature during patient visits, calculating this in the analysis did not affect the researchers’ estimate of the annual decrease in body temperature.
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Another possible explanation for historic drops in body temperature is that bodies no longer need to put a lot of effort into regulating their internal body temperature, due to air conditioners in the summer and heaters in the winter. While the Tsimane’s body temperature changes with the time of year and weather conditions, the Tsimane does not use any advanced technology to regulate his body temperature. However, they receive more clothes and blankets than before.
Understanding the cause of low body temperatures remains an open question for scientists to explore. Whatever the reason, experts claim body temperature is below 98.6 F outside countries like the US and UK – even in rural and tropical areas with minimal public health infrastructure, where infection remains the main cause of death.
They hope the results will inspire more studies on how the improved conditions can lower body temperature. Because it is quick and easy to measure, body temperature can one day prove to be a simple but useful indicator, like life expectancy, that gives new insight into the health of a population.
This report was prepared by Michael Gourven, professor of anthropology, and Thomas Kraft, postdoctoral researcher in anthropology, at the University of California, Santa Barbara.
Source: Science Live
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