We decided to investigate if there is scientific evidence for the normal body temperature being 36.6°C and how experts determined this number.
We will use the Celsius scale in our analysis and convert any figures given in Fahrenheit to Celsius for convenience.
It is worth noting that there is no strict consensus among the scientific community on the exact temperature that should be considered normal. In some Western countries, the norm is 37 degrees rather than 36.6 degrees. We were unable to determine the origin of the number 36.6 in popular belief since medical encyclopedias either cite 37 degrees or provide a range of temperatures considered normal. Additionally, we could not find any literary or cinematic sources that perpetuated this misconception.
The origin of the first “benchmark” numbers is unclear. However, in the mid-19th century, German scientist Carl Wunderlich conducted a study in which he measured the axillary temperature of 25,000 people. He summarized the data and derived an average value of 37 degrees. It is important to note that even at that time, this number was not considered a benchmark, but rather an “average across the board.”
The Center for Vaccine Development in Maryland conducted trials of a new vaccine in 1992. The study involved 148 healthy volunteers, consisting of men and women aged 18 to 40, whose body temperature was measured three to four times a day for three consecutive days. The results indicated an average body temperature of 36.8 degrees.
In 2017, a study was conducted in an outpatient department of a major hospital in the US, in which scientists collected temperature readings from 35,000 individuals. The results showed an average body temperature of 36.6 degrees Celsius. However, there was a significant range of values, from 35.3 to 37.7 degrees Celsius. The study participants did not have any infectious diseases, were not taking antibiotics, and were expected to have normal body temperatures.
Earlier, Swedish researchers summarized studies on body temperature in healthy individuals conducted from 1935 to 1999. The range of values was even greater, from 33.2 to 38.1 degrees Celsius.
The variability in body temperature values could be attributed to the method used to measure temperature. For instance, oral temperature may be lower than rectal temperature, while axillary temperature may be even lower. This is because the skin cools down to some extent in the air, hence the temperature measured inside the body will always be higher than the outside temperature.
Moreover, several factors can affect body temperature, making it vary significantly. Women, for instance, tend to have slightly higher body temperatures than men. Those taking contraceptive pills containing progesterone may experience a further increase of up to 0.6 degrees Celsius. Menopausal women may also experience a rise in body temperature during hot flashes. Age is another significant factor, with older people having lower body temperatures than younger people. Some studies suggest that body weight may also impact body temperature, with individuals diagnosed with obesity tending to have lower body temperature.
The timing of temperature measurements is also important, as the body naturally heats up and cools down by 0.25-0.5 degrees Celsius during the day. Oral temperature should be measured at least 30 minutes after smoking, eating, and consuming hot or cold drinks, while physical exertion or taking a hot bath can influence the results, requiring an hour of wait time before taking any measurement.
A recent theory proposed by scientists from Stanford University suggests that the so-called “average temperature” of the human body has been decreasing over time. The researchers analyzed data from three different periods: 1860-1940 (based on military records, medical records, and Civil War veteran pension lists in the United States), 1971-1975 (results of the National Health and Nutrition Examination Survey in the United States), and 2007-2017 (data from adult patients visiting Stanford Health Care).
Their findings indicated that over a span of 157 years, the average orally measured temperature has decreased by almost half a degree Celsius and now stands at around 36.4 degrees Celsius.
According to the scientists from Stanford University, there are two potential reasons for the decrease in average body temperature over time. Firstly, they suggest that modern thermometry may simply be more accurate than in the 19th century. However, the more likely explanation, in their opinion, is that body temperature is decreasing due to improved living conditions such as comfortable indoor temperatures, improved hygiene, and accessible healthcare.
It should be noted that Wunderlich’s study was based on presumably healthy individuals, but at that time, diseases such as tuberculosis, syphilis, dysentery, and others were much more prevalent, which may have increased body temperature. These diseases may not have been immediately apparent, and therefore, could have influenced the results of the study.
It is important to note that 36.6 degrees Celsius cannot be considered as the absolute norm for every healthy person at any given time, as it is an average value. Furthermore, initial calculations showed that this value was different. Additionally, body temperature can be influenced by various factors such as time and method of measurement, age, weight, intake of certain medications, and even gender. Studies indicate that the difference in temperature values among different individuals can be as high as several degrees.
Responses