Why Does Body Temperature Drop as We Age?

It is not that the elderly have less fever. However, because they naturally have a “cooler” body, increased body temperature is often not taken as a symptom of something more serious in this age group. And it is that, what happens is that as we age, the average body temperature tends to drop. The difference can be up to 1ºC compared to adults and adolescents.

In other words, if the older person is normally at 36ºC and, on a given day, it goes up to 37.1ºC, this may already represent a febrile state, even if the diagnosis of fever only occurs around 38ºC in the youngest. This confusion, in turn, can make it difficult and delay the diagnosis of common or more serious diseases from the sixth decade of life, such as urinary tract infections and pneumonia.

Contrary to what happens with children, fever should not be seen as the main symptom among the elderly, point out the geriatricians consulted by BBC News Brazil. In this group, ailments such as prostration, difficulty with balance, mental confusion and frequent falls can be the first symptoms of an illness.

Paying attention to these and other signs, in addition to checking the temperature from time to time, are ways to detect various problems early and initiate treatment, if necessary.

But what is the reason for this change in temperature?

Decrease of 0.15ºC per decade- A couple of articles published by Santa Casa de São Paulo in 2010 delved into this topic. By analyzing hundreds of records, the researchers concluded that the average temperature of a healthy young adult is 37°C, and this normal range is between 36.3°C and 37.5°C. In the elderly, the mean is 36.1ºC, with a variation of 0.21ºC up or down. Studies also indicate that there is a “0.15ºC drop in temperature for each decade of life”.

Causes of temperature drop

But what is behind this natural cooling of the body? The researchers explain that there are 3 main reasons for this:

The first has to do with the changes of aging: the metabolism slows down, there is less muscle mass, the blood vessels become narrower, the nervous system loses part of its ability to retain heat… “We have a kind of thermostat in the hypothalamus, one of the regions of the brain. And this controls the temperature of our body”, explains the geriatrician Marcelo Altona, from the Hospital Israelita Albert Einstein, in São Paulo. “Throughout the aging process, this natural thermostat can be altered”, he adds.

Marco Túlio Cintra, vice president of the Brazilian Society of Geriatrics and Gerontology, points out that the hypothalamus often continues to function properly during aging. In these cases, the change in temperature involves the simple loss of heat to the environment. “The elderly have more difficulty retaining heat in the body, due to the changes that occur in the skin and fat cells”, explains the doctor.

Doctor with a patient

Second, this group is most often affected by diseases that affect temperature regulation; for example, diabetes, neurological disorders, malnutrition, and sarcopenia (progressive loss of muscle mass). In addition, the use of some medications and immobility related to locomotion problems also influence this process.

Third, the difficulty of measuring temperature in this age group can lead to underestimated results (when the number on the thermometer is lower than the actual temperature). This is because the areas of the body where the mercury thermometer is placed change over the years. In the armpit, excess sweat, skin folds, and fat can interfere. The same thing happens in the ear, if there is a buildup of wax in the ear canal. In the mouth, the lack of some teeth, salivation problems or the difficulty in keeping the thermometer stable are factors that complicate the situation. In the anus, the last alternative on the list, the barrier is the inconvenience of inserting the thermometer there.

Cerebro humano, con el hipotálamo destacado en rojo

One option is the most modern digital devices, which measure on the forehead, but they are more expensive and you have to be careful to change the battery when necessary.

Avoid confusion

Difficulty at measuring temperature correctly -or lack of knowledge about what the normal temperature limit is in an older person- can pose a health threat. This is because an elderly person may have pneumonia or another serious illness and, because they do not have a temperature considered high, do not undergo a medical evaluation.

This confusion delays the diagnosis of diseases that, if detected early, would require less invasive and more effective treatment, such as pneumonia and urinary tract infections. “Unlike what happens with children, fever is not among the main symptoms of infection in the elderly. Often, they have a normal temperature or even hypothermia”, warns Cintra. “The caregiver and the elderly themselves must be attentive to other signs, such as prostration, balance changes, mental confusion, frequent falls… In many cases of urinary tract infection in people over 60 years of age, the only sign is an increase in accidents and falls”, he says.

“If the average temperature of an elderly person is 35.5ºC or 36ºC, and it is 36.9ºC or 37ºC, it is already a sign that it is necessary to monitor it more closely”, says Altona. “In very frail or very old people, small changes in vital signs, such as temperature, blood pressure and heart rate, already require greater care”, says the specialist.

Continuous record

One guideline that may be helpful for some people is to take a continuous temperature record. If the thermometer is used once every 15 days, or once a month, it is possible to know what the average healthy temperature is and to notice when the body is warmer than normal. That is, if the individual is always at 36ºC and, on a given day, appears with 37.2ºC, this may represent an alarm signal depending on the case, although it is not considered fever in other age groups.

But Cintra believes that this monitoring must be very well guided and strictly follow the guidelines of a health professional and the thermometer manufacturer. “Taking a fever all the time can be an unnecessary source of stress”, she notes. “This habit is useful in some cases, but it is not indicated for everyone”. If recommended, these regular temperature measurements should always be taken at the same place on the body and, if possible, with the same device.