When is body temperature too low?

On call

Q. I am 82 years old and in good health. At my regular doctor visits, my temperature has been around 96.5° F. Is that too low?

A. Normal body temperature is not a single number, but rather a range of temperatures. The average normal body temperature is most often said to be 98.6° F (37° C). This may have been correct when it was first determined 150 years ago. But our bodies have changed.

Recent research confirms the decline in average body temperature over many decades. In one study, average temperature of 96 adults over two weeks ranged from 35.2°C (95.4°F) to 37.4°C (99.3°F). Given this wide variation, knowing your own average temperature when you are feeling well is more valuable than an arbitrary number.

Several factors may lead to a lower body temperature in some older people. For instance, as you age, you lose fat under the skin in your extremities and your skin becomes drier; both of these changes cause loss of body heat. Metabolism, which also generates heat, tends to slow as you age. Medications, including beta blockers and antipsychotic drugs, also may lower body temperature, as can an underactive thyroid gland.

Because of their lower baseline temperatures, older people need to be careful to avoid prolonged exposure to the cold, which may lead to hypothermia, which occurs when your body loses heat faster than it can produce it and causes a dangerously low body temperature.

Image: Kameleon007/Getty Images