Advance with MUSC Health

Extreme Heat and Our Vulnerability to it as We Age

Joseph Gerald (Jerry) Reves, M.D.
June 01, 2021
NWS heat index
Heat Index with health implications. Heat index is calculated from the relative humidity and the temperature. Note that a forecasted heat index above about 103 is dangerous to health. From NOAA.

July and August historically bring the highest heat and humidity to Charleston and its environs. This means that people over 50 years of age should be alert to the forecasted temperature and humidity, better known as the heat index. Older people are less tolerant of the special hazard that a high heat index brings. Extreme heat is temperatures much hotter and humid than average and accounts for the largest number of weather related deaths in the U.S. Many of these are in the elderly.

What is the Heat Index?

The heat index is a calculation based on the temperature in the shade and the relative humidity. In lay terms it is explained as "apparent temperature" because high humidity makes the temperature seem higher than it is and when the humidity is low, the temperature feels less hot. The heat index is more than a calculation, however, because it has human health consequences as shown in the figure. The dark red zones of the heat index show extreme danger, orange danger, and yellow caution. Thus, when the daily or 3 day weather forecast comes out, look at the heat index. It is the best indicator of the danger of the forecasted temperature and humidity. A heat index higher than 103 is dangerous to our health. 

Why is Heat Index Used to Predict Health Status?

The human has several ways to cope with elevated temperatures and to avoid over-heating. These include perspiring, vasodilation, increased cardiac output, and thirst. Perspiration (sweating) evaporates from the skin and this cools the skin to combat the higher temperature. However, when the humidity is high this essential, first-line method of cooling is inhibited since there is less evaporation when the humidity is high. Thus, the heat index is a useful way to warn people of the dangers of a temperature that without high humidity may not seem dangerous.

What Makes the Elderly More Susceptible to Heat?

There are several normal physiologic factors of normal aging that predispose to susceptibility to increased heat. First, as we age our skin is less able to perspire compared to younger people. We lose that first, important mechanism of controlling our temperature in a hot environment. Elderly are also often on diets that restrict salt a major component in perspiration. Also, medicines that many elderly take like diuretics and other heart/vascular drugs can impair the body's normal response to heat. Cardiac output is often reduced with age as are the reflexes that increase the cardiac output in response to heat. This means that the heat building up within our body cannot be dissipated by the increased cardiac output and dilation of our veins under the skin. This means that a second, important mechanism for combating increased heat is diminished. Being either overweight or underweight also predisposes to inability to help cooling in the heat. Drinking alcohol and caffeinated beverages also makes you more vulnerable to heat.

Strategies to Deal with Extreme Heat

There are many ways to mitigate the effects of extreme heat. The CDC and NOAA have compiled a simple list of actions to take when under an extreme heat warning (see the table.)

These are common sense and generally easy for most people to do. The first is stay out of the heat and sun. Stay in a well ventilated, air conditioned room. Avoid going outside in the middle of the day (between 10:00 a.m. and 4:00 p.m). Do not engage in strenuous exercise or other activities. These raise the body temperature and a high heat index makes it less possible to reduce the heat of these activities. It is important to wear light colored and loose fitting clothes of synthetic materials rather than cotton or certainly wool. Staying hydrated is critical to preserving the body's ability to cope with the elevated temperature. Perspiration tends to decrease hydration so it is critically important to drink plenty of water and/or sports drinks that have salt, potassium and other ingredients proven to preserve essential internal fluid volume. My practice is to make my own fluid replenishment solution by diluting Gatorade in half or mixing the powered Gatorade with more water than recommended to end up with a diluted solution. When outside stay in the shade if possible. Never leave anyone or a pet in a closed car when the temperatures are above 70.

1  Stay in air conditioned room
 2  Avoid strenuous activities
 3  Wear light, loose clothing
 4  Stay hydrated with drinking fluids
 5  Monitor for heat symptoms like cramps, loss of sweating, temperature > 103
 6  Never leave person or pet in closed care
 7  Check on others

Other Steps to Remain Cool in the Heat

When staying indoors, pull shades down be sure the house has proper weather stripping. Consider installing or running an attic fan. Take a cold water shower if you feel over heated and drink iced water. Be aware that if the ambient temperature is above 95 degrees, running a house floor fan may actually inhibit your ability to recognize the severity of an elevated body temperature. Measure your temperature and call your physician or 911 if your temperature is over 103, you are no longer sweating, have a rapid, strong pulse, and your skin is hot and dry (symptoms of heat stroke).

The Bottom Line

July and August are the times of year we are most likely to experience extreme heat to which older people are vulnerable. Keep an eye/ear out for dangerous heat index advisories from the weather bureau and protect yourself from this seasonal threat to our health!

About the Author

Joseph Gerald (Jerry) Reves, M.D.

Keywords: Healthy Aging