Aging and body temperature

What is the normal body temperature?

It was originally thought to be exactly 37.0 degrees C (98.6 degrees F), according to the pioneering work in clinical thermometry by Carl Wunderlich. However, it’s actually lower than that, at least according to oral measurements back in 1992. The average measurement at that time was 36.8 degrees C (98.2 degrees F). It can also vary due to a lot of factors.

Different devices and different body areas

Since then, new devices for measuring body temperature have been developed. More recent studies report the following ranges:

97 degrees F to 99.8 degrees F (mean 98.4 degrees F), oral measurements in Pakistani population.
35.1 to 36.4 degrees C (95.3-97.6 degrees F), mean axillary temperatures in elderly patients

The most common method of measuring body temperatures are:

Oral temperature
Rectal temperature
Tympanic (ear) temperature
Axillary (under the arm) temperature
Field forehead temperature
Temporal (temple) temperature

Studies revealed that different devices and methods of measurements vary considerably. The US National Athletic Trainers’ Association recommends the use of rectal temperature as the criterion standard for recognizing exertional heat stroke or hyperthermia for indoor as well as outdoor sports.

Different times of the day

Aside from variability due to different measuring techniques, body temperature can vary at with the time of the day, with low values in the morning and high values in the evening.

Other factors that cause variations

Physical activity increases body temperature. Women have generally slightly higher temperatures than men. The 1992 study reported a “trend toward higher temperatures among black than among white subjects.”

Temperature and age

Finally, several studies reported that body temperature changes with ages. It seems that there is a noticeable drop in body temperature with each decade of life lived. This drop in temperature can have some consequences in the treatment o of elderly patients. Fever caused by infections, for example can go unnoticed. A study by Turkish researchers reported:

The mean age of the subjects was 77.2, SD 7.3. In the 133 older subjects, the mean axillary temperatures ranged from 35.1 to 36.4 degrees C (95.3-97.6 degrees F). The mean temperatures for those aged 65-74 was higher than in those aged 75-84 (p < 0.001) and those aged 85 and older (p < 0.001) at 6 p.m. but not at 8 a.m. or 2 p.m. We concluded that older people have mean axillary body temperatures lower than the reference point of 36.5 degrees C (97.7 degrees F)… When assessing body temperature, it is important to take the age of the patient into consideration. Also, the reference point of 36.5 degrees C is inappropriate in older people, especially when diagnosing a febrile illness.

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