The thyroid hormones regulate the body temperature. As soon as there is an underactive thyroid, the basal temperature gets lower. Dr. Broda Barnes, in the 1970's, developed this concept, relayed by Dr. Ray Peat. When the basal temperature is inferior to the norms, and stable from one day to another, there is a great probability of lower activity of the thyroid. In 1990, Dr. Denis Wilson developed a concept attributed to low body temperature, the Wilson Temperature Syndrome, also known as Wilson's thyroid syndrome. Although controversial, I will discuss at length in the chapter on treatment because it has some interesting aspects.
Waking oral temperature should be 36.6° C (97.8 F), then raises to 37° – 37.2° C (98.6 - 98.9 F) during the following 10 hours. The optimum time to check the temperature is between 11 to 15 o'clock, and 20 minutes after lunch, as the thyroid activity is at its highest.