98.6
°F versus new normal: why is body temperature declining over time?
For
several years now, doctors and researchers have realized that 98.6 ° F is not
really the “normal” body temperature it was thought to be. Studies show in the
US and Europe they have found that body temperature drops over time. But has
this trend caught on to the good of the outside world? Indeed, body
temperatures have plummeted in Bolivia's indigenous population, a 16-year study
is funded. Published in Science Advances, this study also looks at possible
causes that may cause this decline in the general population. What is the
charge against taking 98.6 ° F as normal body temperature? German physician
Carl Reinhold August Wunder lich, who in 1851 pioneered the use of a clinical
thermometer, took estimates of more than 25,000 patients and published his findings
in 1868, in which he concluded that the human body temperature was 98.6 ° F. In
recent years, however, various studies have found that the human body
temperature is measured differently, including 97.7 °, 97.9 ° and 98.2 ° F.
In
one such large-scale study, we found that temperatures among Americans had
plummeted in the last two centuries. So, what new lesson can we learn? In
previous studies, the reasons for the drop in body temperature were unclear,
and it was not known whether the temperature below 98.6 ° F was
"normal" outside of the high-income countries. The new study looked
at 18,000 body temperature in 5,500 people in Tsimane, an indigenous nation in
the Bolivian Indian Amazon. "The Tsimane are indigenous farmers who eat food
grown in tropical and subtropical areas - ranging from familiar ones such as
cold or pneumonia, to unusual ones such as hook worm and tuberculosis,"
said lead author Michael Gurven, a sociologist at the University of California,
Santa Barbara.
Excessive
exposure to infection can lead to high fever, which in turn can lead to high
body temperature. “From previous studies, we also know that Tsimane suffers
from high inflammation due to this high infection load. And then we were
expecting to find out that body temperatures would be higher than Tsimane than
in the United States, the UK and Germany. Instead, the study found that body
temperature among Tsimane decreased by 0.09 ° F per year; averaged about 97.7 °
F today.
This
decline in less than two decades, researchers noted, was almost identical to
what was seen in the US more than two centuries ago. What could be the reasons
for this? The study looked at a number of theories on the potential for global
warming, and it also examined this by finding out what they found in the
Tsimane people.
BETTER
HEALTH CARE: One hypothesis
is that improved hygiene and health care in high-income population groups have led
to fewer infections over time and, in turn, to lower body temperature. While
the Tsimane live a rural life style with a relatively low access to health care,
they do have better access than they did two decades ago. Indeed, some
infections were found to be associated with higher body temperature. But when the
statistical model adjusted the temperature findings for infection, it found that
reduced infection alone could not explain the declines. “This is to say that
the decline in body temperature over the duration of the study is not altered by
considering patient characteristics, including their medical diagnoses.
LOWER
INFLAMMATION: People
use anti-inflammatory drugs such as ibuprofen more frequently than earlier.
Again, even after accounting for biomarkers of inflammation, body temperature
declines over time remained among the Tsimane.
BRIEFER
ILLNESS: Since
people have greater access to treatment, has it reduced the duration of infection?
That was another hypothesis the study tested. The findings among the Tsimane, indeed,
were consistent with this argument. If a study participant had a respiratory
infection in the early stages of the 2002-18 study, it led to having a higher
body temperature than the temperature if they had the same infection more
recently.
BODIES
WORKINGLESS: Another
theory is that people are healthy, so their bodies may be less active in
fighting infections. Also, our bodies may not need to work as hard as they used
to in order to control the internal heat due to cooling air and winter
temperatures. The people of Tsimane do not use such advanced technology but
have more access to clothing and bedding. So, what are the consequences?
Collectively, the findings emphasize that there is no single cause that can
explain decline. Investigators say it may be a combination of factors - all
pointing to improved conditions.
Researchers
do not expect that their findings will influence how doctors use body
temperature readings. Doctors have already acknowledged that there is no
‘normal’ body temperature in all people at all times. Among its limitations,
the study used the same type of thermometer, but not the same thermometer
throughout the 16 years. In the early years of the study, the sample size was
small. The study did not focus on pregnancy or breastfeeding, or the time of
day when body temperature was recorded.