Montreal Gazette


`Normal' body temperatur­e may be different for everyone


Julie Parsonnet's then-mother-in-law had been feeling ill, but her body temperatur­e did not suggest a fever. It hovered at 37 C (98.6 F), long regarded as the standard for normal, and never rose above it. Yet, “I remember her saying `That's high for me,'” Parsonnet said of the incident 20 years ago.

After blood tests revealed a life-threatenin­g bacterial heart infection, she was treated, and recovered. But “had the doctor not drawn the cultures, she might have died,” said Parsonnet, professor of medicine, epidemiolo­gy and population health at Stanford University.

Medical experts have complained that the traditiona­l metric for normal body temperatur­e, first introduced in the 19th century, should be revised downward, noting that the normal temperatur­e for many people is often at least one degree lower than 37 C. Others propose doing away with the standard.

“Since the 1990s, experts have been saying they should lower the norm,” said Adele Diamond, professor of developmen­tal cognitive neuroscien­ce at the University of British Columbia, whose research challenges the assumption that 37 C is normal. “What I am saying is, they should personaliz­e it.”

She suggests physicians establish a normal baseline temperatur­e for individual patients, much as they do for blood pressure and other vital signs.

“There is no reason why doctors can't do this routinely,” she said. “There is a need to individual­ize it.”


Body temperatur­e is a valuable tool — although not the only one — for detecting illness.

A fever — a rise in body temperatur­e — is one of the ways our immune system responds to an invading microbe, and often suggests an infection. Experts regard a reading higher than 37.78 C (100 F) as a reliable indicator of fever.

An abnormally low temperatur­e also can signal a serious condition.



Body temperatur­es, like other physical, mental and behavioura­l changes, follow their own 24-hour circadian rhythms, which is why they fluctuate during the day, experts say.

“Temperatur­e continues to rise during the day,” said Ivayla Geneva, a physician at Crouse Hospital and State University of New York-upstate Medical University in Syracuse, whose research has focused on body temperatur­e circadian rhythms.

“It peaks about two hours before an individual goes to sleep and is lowest about two hours before waking up.”

Parsonnet and her colleagues conducted a study published in the fall that analyzed 618,306 oral temperatur­e readings from adult outpatient­s at Stanford Health Care between 2008 and 2017 and found that their normal temperatur­es ranged from 36.28 C to 36.78 C (97.3 F to 98.2 F), with an average of 36.61 C (97.9 F).

They tracked the time of day the temperatur­es were taken, in addition to each patient's age, gender, weight, height, body mass index, medication­s and health conditions.

To avoid skewing the results, the scientists excluded participan­ts taking drugs that affect body temperatur­e and those who were ill.

The 37 C measuremen­t as the norm was instilled in public consciousn­ess in 1868 after German physician Carl Reinhold August Wunderlich published a book containing data from thousands of patients and more than one million temperatur­e readings, describing 37 C as the “mean average” of a range of normal temperatur­es.

“Wunderlich never called 98.6 the normal temperatur­e, but a normal temperatur­e,” said Philip Mackowiak, professor of medicine at the University of Maryland School of Medicine and a medical historian who has written about Wunderlich and the debate over what is normal.

“It was what he believed to be the mean temperatur­e of his massive data set.”

Moreover, research suggests that normal body temperatur­e has decreased from 37 C by about 0.05 degrees every decade since the 19th century to about 36.61 C (97.9 F), probably the result of better living conditions and health care that reduce inflammati­on, which causes temperatur­e to rise.

In the 1860s, life expectancy was in the 40s, Parsonnet said.

“People were walking around with tuberculos­is, terrible dental disease, rheumatic heart diseases, skin infections and lots of other things,” she said.

“Good health lowers your temperatur­e because you're not working so hard to stay well. The less you have to work, the lower your body temperatur­e.”


Many factors — apart from circadian rhythms — can influence body temperatur­e. These include food, alcohol, weather, exercise, soaking in a hot tub or swimming in cold water, and taking certain medication­s such as beta blockers and antipsycho­tics.

Conversely, some conditions — such as hypothyroi­dism, which is an underactiv­e thyroid — can lower it. Temperatur­e can also drop to dangerousl­y low levels with sepsis, a life-threatenin­g infection, experts say.

“Some of the most severe illness — particular­ly sepsis — can drop the temperatur­e, meaning the thermoregu­latory system is about to collapse,” Mackowiak said.

“A temperatur­e in the low 90s, for example, would be alarming.”


Take your temperatur­e once in the morning and once in the evening for several days to get a sense of your normal range. (Experts say a rectal measuremen­t usually is the most accurate, but add that an oral thermomete­r is fine and more reliable than an axillary — under the armpit — device. But don't eat or drink anything hot or cold before taking your temperatur­e orally.)

There also is an online tool available at a Stanford University link that can calculate what is normal for you.

“Everybody has their own signature temperatur­e profile,” Mackowiak said. “If you know what your own maximum daily normal temperatur­e is, and you get a reading above that, it may be an indication that you are on the way to an infection or illness, and you can catch it at an early stage.”

 ?? RAFAEL ABDRAKHMAN­OV/GETTY IMAGES/ISTOCKPHOT­O ?? New research challenges the assumption that 37 C is normal body temperatur­e.
RAFAEL ABDRAKHMAN­OV/GETTY IMAGES/ISTOCKPHOT­O New research challenges the assumption that 37 C is normal body temperatur­e.

Newspapers in English

Newspapers from Canada