Dear Doctors: I can’t get my husband and his brother to take hot weather warnings seriously. They’re in good shape and think that since they’re younger (29 and 33) that it’s OK for them to go out hiking in hot weather. Can you talk about why it’s dangerous for everyone when there’s a heat wave?
Dear Reader: It can be easy to underestimate the risks of physical exertion in hot or even warm weather. The early symptoms of heat-related illness, such as sweating and flushed skin, are the same as what happens when you’re simply a bit too hot. The danger lies in how easy it is for overheating to progress to severe heat-related illness if you don’t address early symptoms.
On the milder end of the spectrum is heat stress. Symptoms include excessive sweating and flushed skin. The body sweats to create an evaporative effect. Flushing sends blood to the surface of the body where the blood can cool down quicker. Other symptoms of heat stress can include headache, muscle cramps, weakness and dizziness. These occur because an increase in core temperature has begun to adversely affect the functioning of the body’s metabolic processes.
Heat stress is not an immediate danger to health. However, it’s a loud warning that the body is struggling to stay cool. When core temperature rises much beyond the optimal range of 97 to 99 degrees Fahrenheit, the three-dimensional enzymes that power biochemical reactions in the body begin to lose their shape. This impairs their function and leads to the symptoms of heat exhaustion and heat stroke.
Heat stroke is a medical emergency that can cause lasting damage to the tissues of the heart, kidneys, liver and brain. Without prompt medical intervention, heat stroke can lead to death. We will go into greater detail about these in an upcoming column.
Keeping a safe core temperature in hot weather depends on a few factors. Air temperature is important, of course. So is sunlight, which is radiant energy that directly heats the skin. Our muscles also generate heat. So exercising in hot and sunny conditions exposes you to three separate sources of heat. Then there’s humidity, which affects how much evaporative cooling can occur. Adding up all these factors, it can be all too easy to cross the threshold from mild discomfort to severe heat illness.
Your husband and brother-in-law are partially correct: Being healthy and in good physical shape can improve tolerance to hot weather. However, the metabolic cascade of severe heat-related illness occurs at a cellular level. Once it begins, your level of fitness won’t matter. The only way to stay safe while exercising in hot weather is to protect core body temperature. Avoid peak heat and be aware of humidity. Wear light, loose layers to shield from the sun. Hydrate before, during and after exertion. If you have symptoms of heat stress, address them immediately.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)