98.6 F — It Is Not The Average Body Temperature Anymore
February 10, 2020 at 5:16 p.m.
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In truth, each of us has his or her own individual "normal" body temperature, which may be slightly higher or lower. Our bodies also constantly adapt their temperature to environmental conditions. It goes up when we exercise, for instance. And it is lower at night and higher in the afternoon than in the morning.
Strictly speaking, body temperature refers to temperature in the hypothalamus, a small region of the brain located at its base and in the vital internal organs. Because we cannot measure the temperature inside these organs, temperature is taken on parts of the body that are more accessible, i.e., orally, rectally, vaginally, axillarily (under the armpit) or in the ear. Ear and rectal temperatures tend to be a half degree higher than oral temperature. Axillary temperature tends to be one degree lower.
There is a recent study from Stanford University that analyzed 677,423 temperatures collected from 189,338 individuals, it indicated that In the United States, the normal, oral temperature of adults is, on average, lower than the widely accepted 98.6 degrees F ( 37 degrees C) established in the 19th century by Professor Carl Reinhold August Wunderlich in Germany.
Professor Wunderlich pioneering and extensive work was published in 1851 and based on results from an astounding 25,000 patients. Dr. Wunderlich reported that “The average normal temperature of the healthy human body in its interior, or in carefully covered situations on its surface, varies, according to the plan of measurement, from 98.6 degrees to 99*5 degrees F. (37 degrees to 37*5 degrees C). It is about 98*6 degrees in the well-closed axilla, and a few tenths of a degree higher in the rectum and vagina.”
The Stanford University comprehensive study determined that body temperature has decreased over time. It provides a framework for understanding changes in human health and longevity over the past 157 years. Using measurements from three cohorts—the Union Army Veterans of the Civil War measured in the years 1860–1940, the National Health and Nutrition Examination Survey taken in 1971–1979, and the Stanford Translational Research Integrated Database Environment from 2007–2017 — the researchers determined that mean body temperature in men and women, after adjusting for age, height, weight and, in some models, date and time of day, has decreased monotonically by 0.03 degrees C per birth decade. A similar decline within the Union Army cohort as between cohorts, makes measurement error an unlikely explanation.
There have also been at least 27 other modern studies reporting mean temperatures uniformly lower than Wunderlich’s estimate. Recently, an analysis of more than 35,000 British patients with almost 250,000 temperature measurements, found mean oral temperature to be 36.6 degrees C, confirming this lower value. Remaining unanswered is whether the observed difference between Wunderlich’s and modern averages represents true change or bias from either the method of obtaining temperature (axillary by Wunderlich vs. oral today) or the quality of thermometers and their calibration.
Wunderlich obtained his measurements in an era when life expectancy was 38 years and untreated chronic infections such as tuberculosis, syphilis and periodontitis afflicted large proportions of the population. These infectious diseases and other causes of chronic inflammation may well have influenced the ‘normal’ body temperature of that era. Wunderlich’s book On the Temperature in “Diseases: A Manual of Medical Thermometry” published in 1871 has been translated into English.
The question of whether mean body temperature is changing over time is not merely a matter of idle curiosity.
Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). The Stanford group speculated that the differences observed in temperature between the 19th century and today are real and that the change over time provides important physiologic clues to alterations in human health and longevity since the Industrial Revolution.
Final Thoughts
According to a recent Wall Street Journal article the Stanford study could offer a clue about other physiological changes that have occurred over time. The article also noted that the accumulation of evidence on body temperature should change medical norms, guidelines and thresholds about when and how to treat patients. The article does note, however, that a thermometer reading matters less than how we feel. “If you are sick, you’re sick, regardless of your temperature.”
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at [email protected].
In truth, each of us has his or her own individual "normal" body temperature, which may be slightly higher or lower. Our bodies also constantly adapt their temperature to environmental conditions. It goes up when we exercise, for instance. And it is lower at night and higher in the afternoon than in the morning.
Strictly speaking, body temperature refers to temperature in the hypothalamus, a small region of the brain located at its base and in the vital internal organs. Because we cannot measure the temperature inside these organs, temperature is taken on parts of the body that are more accessible, i.e., orally, rectally, vaginally, axillarily (under the armpit) or in the ear. Ear and rectal temperatures tend to be a half degree higher than oral temperature. Axillary temperature tends to be one degree lower.
There is a recent study from Stanford University that analyzed 677,423 temperatures collected from 189,338 individuals, it indicated that In the United States, the normal, oral temperature of adults is, on average, lower than the widely accepted 98.6 degrees F ( 37 degrees C) established in the 19th century by Professor Carl Reinhold August Wunderlich in Germany.
Professor Wunderlich pioneering and extensive work was published in 1851 and based on results from an astounding 25,000 patients. Dr. Wunderlich reported that “The average normal temperature of the healthy human body in its interior, or in carefully covered situations on its surface, varies, according to the plan of measurement, from 98.6 degrees to 99*5 degrees F. (37 degrees to 37*5 degrees C). It is about 98*6 degrees in the well-closed axilla, and a few tenths of a degree higher in the rectum and vagina.”
The Stanford University comprehensive study determined that body temperature has decreased over time. It provides a framework for understanding changes in human health and longevity over the past 157 years. Using measurements from three cohorts—the Union Army Veterans of the Civil War measured in the years 1860–1940, the National Health and Nutrition Examination Survey taken in 1971–1979, and the Stanford Translational Research Integrated Database Environment from 2007–2017 — the researchers determined that mean body temperature in men and women, after adjusting for age, height, weight and, in some models, date and time of day, has decreased monotonically by 0.03 degrees C per birth decade. A similar decline within the Union Army cohort as between cohorts, makes measurement error an unlikely explanation.
There have also been at least 27 other modern studies reporting mean temperatures uniformly lower than Wunderlich’s estimate. Recently, an analysis of more than 35,000 British patients with almost 250,000 temperature measurements, found mean oral temperature to be 36.6 degrees C, confirming this lower value. Remaining unanswered is whether the observed difference between Wunderlich’s and modern averages represents true change or bias from either the method of obtaining temperature (axillary by Wunderlich vs. oral today) or the quality of thermometers and their calibration.
Wunderlich obtained his measurements in an era when life expectancy was 38 years and untreated chronic infections such as tuberculosis, syphilis and periodontitis afflicted large proportions of the population. These infectious diseases and other causes of chronic inflammation may well have influenced the ‘normal’ body temperature of that era. Wunderlich’s book On the Temperature in “Diseases: A Manual of Medical Thermometry” published in 1871 has been translated into English.
The question of whether mean body temperature is changing over time is not merely a matter of idle curiosity.
Human body temperature is a crude surrogate for basal metabolic rate which, in turn, has been linked to both longevity (higher metabolic rate, shorter life span) and body size (lower metabolism, greater body mass). The Stanford group speculated that the differences observed in temperature between the 19th century and today are real and that the change over time provides important physiologic clues to alterations in human health and longevity since the Industrial Revolution.
Final Thoughts
According to a recent Wall Street Journal article the Stanford study could offer a clue about other physiological changes that have occurred over time. The article also noted that the accumulation of evidence on body temperature should change medical norms, guidelines and thresholds about when and how to treat patients. The article does note, however, that a thermometer reading matters less than how we feel. “If you are sick, you’re sick, regardless of your temperature.”
Max Sherman is a medical writer and pharmacist retired from the medical device industry. He has taught college courses on regulatory and compliance issues at Ivy Tech, Grace College and Butler University. Sherman has an unquenchable thirst for knowledge on all levels. Eclectic Science, the title of his column, touches on famed doctors and scientists, human senses, aging, various diseases, and little-known facts about many species, including their contributions to scientific research. He can be reached by email at [email protected].
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