Humans Cooler by 0.4°C Over 200 Years... Body Temperature from 37°C to 36.6°C

Stanford Research Team Analysis... Between 36.2 and 36.7 Degrees
Males Lower Than Females, Decreases With Age
37 Degrees Standard 200 Years Ago... "Not That High Anymore"

A study has revealed that 37 degrees Celsius (98.6 degrees Fahrenheit) may not be the normal body temperature for everyone. It varies depending on factors such as age, gender, height, and weight.

Dr. Julie Parsonnet, a professor of infectious disease epidemiology at Stanford University School of Medicine, and her research team recently analyzed oral temperature measurement data from a total of 618,000 visits by adult outpatients to the Stanford Medical Center between 2008 and 2017. This finding was reported by the U.S. health media outlet HealthDay News on the 5th (local time).

The research team tracked changes throughout the day along with each patient's age, gender, weight, height, medications, and health status. They also used machine learning algorithms to identify diseases and medications that could cause abnormally high or low temperatures to ensure that the temperature data was not distorted by illness. As a result, patients with infectious diseases associated with fever, type 2 diabetes, and others were excluded from the analysis. This accounted for about one-third of all patients.

The analysis showed that the normal body temperature for adults varied between 36.2°C and 36.7°C. The overall average was 36.6°C, a value close to the 36.5°C commonly used in Korea. About 25% of the variation in normal body temperature was influenced by age, gender, height, weight, and the time of day.

Normal body temperature was lower in men than in women, decreased with increasing age and height, and increased with weight. It was lowest in the early morning and was most influenced by the warm temperature around 4 p.m. For example, the normal morning temperature of an 80-year-old tall and light-weight man was found to be about 1 degree lower than the normal afternoon temperature of an obese woman in her 20s.

The 37°C standard was established nearly 200 years ago by Carl Wunderlich, a 19th-century German physician, and has been used as a criterion to assess fever or the severity of illness. However, over time, body temperatures in healthy adults have been measured lower. A 2017 study of 35,000 adults in the UK found an average temperature of 36.6°C. In 2019, it was found that the normal temperature in California, USA, was 36.4°C.

However, Dr. Julie Parsonnet, who led the current study, said, "Most people, including doctors, still think the normal body temperature is 37°C," adding, "In fact, normal body temperature varies by person and situation, and temperatures as high as 37°C were rarely observed."

The research team suggested that future studies are needed to establish personalized criteria for fever diagnosis and to investigate whether having a lower or higher normal body temperature affects lifespan. The results of this study were published in the latest issue of the JAMA Internal Medicine.

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