As the planet gets hotter, humans are getting colder. An investigation of the evolution of human body temperature over the last 200 years was recently published by researchers at Stanford University in eLife, an online scientific journal for the life sciences. (1) They found that the average body temperature is going down.
The standard normal body temperature of 98.6 degrees Fahrenheit (37 degrees Centigrade) is no longer correct. Today it’s actually about 1 degree F less than that.
The old normal body temperature was established in 1851 by a German doctor, Carl Reingold August Wunderlich. He carefully measured millions of temperatures under the arms of 25,000 of his patients in Leipzig.
The Stanford investigators using cohorts of Civil War veterans and various more modern sample groups, came up with the observation that average body temperature seems to be decreasing in a straight line steady manner since the earliest sample observations in the United States. Also this is a real thing and not because of differences in thermometers and other technicalities.
One degree on average may seem like a lot but the temperature differences between individuals and times of the day and age and sex and other variables is easily more that 1 degree F. Women can use daily body temperature for example to see when they are ovulating. Recently in this column (Tuesday January 14) we reported on the observation that when you lose weight your body temperature goes down.
But one degree on average of “normal” body temperature is still important and interesting. Human body temperature is a crude measure of 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).
So why is this happening? Every discovery raises more questions than it answers. But the best guess according to these authors is that we have less chronic inflammation in our bodies today. When Dr. Wunderlich made his measurements life expectancy was 38 years and untreatable chronic infections such as tuberculosis, syphilis, and bad teeth were rampant. These infectious diseases and other causes of chronic inflammation may well have influenced the “normal” body temperature of that era. It has been observed for example, that in Pakistan, where life is not as good as here, body temperatures are higher.
Many other things have changed over the time span since the beginning of the industrial revolution. We are taller and fatter and our lives are less brutal less stressful more comfortable and etc. etc. etc…
Is a lower body temperature a good thing? The next big thing might involve a simple cheap trick that readjusts your average body temperature.
Decreasing human body temperature in the United States since the Industrial Revolution
John DiTraglia M.D. is a Pediatrician in Portsmouth. He can be reached by e-mail- [email protected] or phone-354-6605.