Human body temperature to give the most accurate assessment of core body temperature, particularly in hypothermia. In the early 2000s, ingestible thermistors in capsule form were produced, allowing the temperature inside the digestive tract to be transmitted to an external receiver; one study found that these were comparable in accuracy to rectal temperature measurement. In the 19th century, most books quoted "blood heat" as 98 °F, until a study published the mean (but not the variance) of a large sample as . Subsequently that mean was widely quoted as "37 °C or 98.4 °F" until editors realised 37 °C is closer to 98.6
Human body temperature much higher than usual. Hormonal contraceptives both suppress the circamensal rhythm and raise the typical body temperature by about . Temperature also varies with the change of seasons during each year. This pattern is called a "circannual" rhythm. Studies of seasonal variations have produced inconsistent results. People living in different climates may have different seasonal patterns. Increased physical fitness increases the amount of daily variation in temperature. With increased age, both average body temperature and the amount of daily variability in the body temperature tend to decrease. Elderly patients may have a decreased ability to generate body heat during a