Popular Mechanics - USA (2020-07)

(Antfer) #1

Science


▶ Julie Parsonnet, MD, a professor of epidemi-
ology at Stanford University. “We have changed
who we are over the modern era.” She and her team
analyzed more than 670,000 reported tempera-
tures spanning 157 years of measurement and 197
birth years and found that our temperature has
dropped 0.05 degrees Fahrenheit per decade since
the mid 1800s. The study was sparked by a review
of modern temperature studies where patients
uniformly fell below the 98.6-degree Fahrenheit
mark—a signal that something was rotten in the
state of human body-temperature research.
Parsonnet and her team studied three large sets
of data from between 1862 and 2017: temperatures
taken during periodic checkups with Civil War vet-
erans between 1862 and 1930; National Health
and Nutrition Examination results from the early
1970s; and data from the Stanford Translational
Research Integrated Database Environment proj-
ect taken from 2007 to 2017.
Controlling for changes in how temperatures
were taken and advances in thermometry across
the large pool of data, they compared body tem-
perature with birth years and found that the
average body temperature in men and women
has gone down 0.05 degrees Fahrenheit per birth
decade.
In their paper published in the journal eLife,
Parsonnet and her colleagues suggest that a
change in inflammation levels over time is the
most likely explanation for the decrease in
temperature. Inf lammation can be caused by bac-
terial, fungal, or viral infections, surface injuries
like scrapes and punctures, or inf lammatory con-
ditions like cystitis, bronchitis, and dermatitis. As
part of the body’s immune response, inf lamma-
tion produces cytokines and other proteins that
increase metabolism and generate heat.
The development of germ theory (that micro-
organisms can cause disease) and advances in
hygiene have changed how often many of these
conditions occur. Today, the length of bacte-
rial infections is shortened by antibiotics. And
the symptoms of viruses can often be alleviated
with anti-inf lammatory drugs like ibuprofen
and naproxen, which can bring down your body
temperature. Civil War veterans plagued with ail-
ments in the 1800s weren’t as lucky.
Our environment has changed, too. We now
have access to healthier foods and are more


hygienic. We’ve learned to heat and cool indoor
spaces more efficiently, which may also contrib-
ute to a lower metabolic rate. These environmental
changes beget physiological changes. “We’re taller,
fatter, and colder,” Parsonnet says. We also live a lot
longer than the average Civil War veteran.
The world has certainly become a safer, health-
ier place for humans, but the researchers say it’s
hard to single out any one environmental change
that’s lowered our temperatures.
Parsonnet says that changing the human body
creates ensuant mysteries: what are the outcomes,
and how do they change as a consequence of our
actions and environment? “They could be good—
greater life expectancy, for example. They could
be bad—causing obesity and perhaps limiting our
ability to deal with new pathogens,” Parsonnet
says. “Changing fundamentally who we are may
have surprising consequences.”
Parsonnet and her colleagues did not iden-
tify a new average body temperature guideline
in their study. A recent large review, a 2017 study
published in the British Medical Journal, for
example, found the average body temperature
of 35,488 British patients to be around 97.88
degrees Fahrenheit. However, because each per-
son’s own temperature constantly f luctuates and
can be inf luenced by factors like gender, age, and
the time of day, many researchers have questioned
whether an ideal temperature standard should
even exist.

M U C H A S W E H A V E C H A N G E D


THE EARTH ECOSYSTEM, WE


ARE CHANGING OUR OWN ECOSYSTEMS,”


SAYS JULIE PARSONNET, MD, A


PROFESSOR OF EPIDEMIOLOGY AT


STANFORD UNIVERSITY. “WE HAVE


CHANGED WHO WE ARE OVER THE


MODERN ERA.”


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