The idea of what is a normal body temperature was recently re-evaluated in a new paper from a journal called eLife, a publication that is unfamiliar to me.

After seeing this reference in three printed locations, my interest heated up (to around 99.1).

The study was done by doctors and researchers at Stanford University. The classic body temperature number of 98.6 degrees Fahrenheit, 37 degrees centigrade, has held sway since the 1850s. This paper presents data from three groups that record a lower average (keyword!) temperature.

The paper cites the work of Dr. Carl Wunderlich in Leipzig, Germany, who first published his findings from thousands of temperatures taken from armpits (called axillary) of 25,000 patients with a mercury thermometer.

His final work in 1868 established 98.6 F, 37 C, as the normal human body temperature.

The current data was obtained from Civil War Union Army Veterans’ records of 83,900 temps taken between 1862-1930; National Health and Nutrition Examination Survey I, 5,998 temps from the years 1971-1975; and the Stanford Translational Research Integrated Database Environment, 230-261 temps from 2007-2017.

Some of the Stanford findings showed men’s body temperatures on average to be 0.59 C lower than those born in the early 1800s; women’s body temperature lower by 0.32 C from the 1890s to today; and a decline of 0.03 C in average temperature each decade.

One doctor postulated the reasons for the change might include that the average metabolic rate, which indicates how much energy our bodies use over time, has also declined for several reasons.

One thought is the temperatures in our homes have become more equal with heating and air conditioning, lessening the effort our bodies use to maintain a core temperature.

Another possibility that is we don’t live with as many chronic infections, such as tuberculosis, syphilis and periodontal or gum infections, which cause inflammation that raises core temperatures. They didn’t mention that we don’t physically work as hard as we used to.

This is not the first study to question the almost canonized 98.6 number. Medicine has long known that anyone’s temp varies during the course of a day with time of day, called diurnal rhythm, gender, exertion level, health status, female menstrual cycle phase (higher after ovulation), state of consciousness (nothing personal here) and emotional state (not while listening to news).

The place of measurement and the device used changes the number a bit. Even Wunderlich in 1851 recognized a range of normal, 97.7-99.5 F.

Any person’s temperature can vary by a degree from day to day and especially with location of measurement.

Our temperature during a day fluctuates, with the lowest being 4-6 a.m. and the highest about 4-6 p.m. in our latitude. Nocturnal temps go up under an electric blanket (or cuddling with your main squeeze?).

Working night shifts might alter patterns. But I recall some nurses on nights felt cold at the end of their shift, took their own temps and found them lower about 6 a.m. Aging makes your thermostat not work as well, along with everything else. It’s much harder to stay warm. Oral temps vary with what you have just eaten or drunk.

The Mayo Clinic entry under Fever meticulously outlines the importance of always using a digital thermometer. The mercury ones of yore are gone because of concern about mercury exposure if the mercury end bulb would break. Axillary and eardrum or tympanic devices read about a degree lower on average.

The Stanford paper mentioned a compilation of 27 earlier modern studies, which reported the mean temperature to be uniformly lower than Wunderlich’s estimate.

An infectious disease doctor, Philip Mackowiak, found one of Wunderlich’s 1800s thermometers in the Mutter medical Museum in Philadelphia. Tests showed the instrument, mercury-filled glass tube about 9 inches long ran 2.9-3.2 degrees higher than other thermometers of the same period from the museum’s collection. He published his findings in 1992 and 1994, but it didn’t change anything. The temperature at 98.6 still held sway. Another study in the Journal of Internal Medicine, 2018, also found a normal temp closer to 97.7 F.

So, the quandary of trying to define “normal” extends even into the medical realm of body temperature. It seems paradoxical that our bodies might be cooling as our world is melting and heating with climate change. Is normal actually a one-word oxymoron?

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