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 dramatically affect the reading. Temperature is increased after eating or drinking anything with calories. Caloric restriction, as for a weight-loss diet, decreases overall body temperature. Drinking alcohol decreases the amount of daily change, slightly lowering daytime temperatures and noticeably raising nighttime temperatures. Exercise raises body temperatures. In adults, a noticeable increase usually requires strenuous exercise or exercise sustained over a significant time. Children develop higher temperatures with milder activities, like playing. Psychological factors also influence body temperature: a very excited person often has an elevated temperature. Wearing more clothing slows daily temperature change and raises body temperature. Similarly, sleeping with