Diurnal variation in body temperature, (from the 1911 Encyclopædia Britannica Eleventh Edition) ranging from about 37.5 °C from 10 a.m. to 6 p.m., and falling to about 36.3 °C from 2 a.m. to 6 a.m.
Normal human body temperature is a concept that depends upon the place in the body at which the measurement is made. The value of 36.8 °C ±0.7 °C, or 98.2 °F ±1.3 °F is the common oral measurement.1 Rectal measurements, or measurements taken directly inside the body cavity, are typically about a half degree Celsius (1 °F) higher. The core body temperature of an individual also tends to vary during the day and with activity level, with the lowest value in the second half of the sleep cycle; this low point, called nadir, is one of the primary markers for circadian rhythms. In 1861, Carl Reinhold August Wunderlich claimed to measure the temperatures of one million people, and reported the average to be 37 °C.2 In the United States, normal human body temperature is commonly quoted as 98.6 °F, which is an exact conversion of 37 °C.1 In Russia, the commonly quoted value is 36.6 °C (97.9 °F), based on an armpit reading. According to the Russian pharmaceutical chain named 36.6, "36.6 is the ideal body temperature in Centigrade for healthy adults and children".3 References
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