Member Case Study: Heat Stress and Hydration

author : AMSSM

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Heat stress, heat exhaustion, and heat stroke: How do these relate to hydration? Can I be well hydrated and still suffer heat stress?

Question from AdaBug

Heat stress, heat exhaustion, and heat stroke: How do these relate to hydration? Can I be well hydrated and still suffer heat stress? Why is it that once heat stressed, a person is more susceptible to further heat stress/exhaustion?

In my former career, which involved working outside, I have been heat stressed, possibly suffering from heat exhaustion. Looking back over past exertions in heat--with results that ruined the remainder of the day-- I realized it's happened a few times before. Sometimes, after a long treadmill run or other lengthy gym workout, I feel that I am overheated, even though I believe according to urination frequency/color that I'm hydrated. I've been avoiding the hotter hours of the day lately, as I know how sensitive I've become to the heat. So, tell me all about it, doc!

Answer from Arnold M. Ramirez, M.D.

Member AMSSM

By definition, heat related illnesses result from the failure of the body’s normal thermoregulatory mechanisms which are necessarily dependent on the body’s hydration status. Heat is dissipated from the body by a number of different mechanisms such as radiation, convection, conduction, and evaporation. This process is accomplished by circulating blood, which transfers heat away from the body’s core and vital organs to the skin, where is it primarily lost by sweating.

Dehydration will decrease the amount of circulating blood volume that can be used to dissipate heat. Nevertheless, it is possible to develop heat related illness in the absence of dehydration if the rise in the body’s core temperature occurs faster than it is able to dissipate the heat. The susceptibility of an individual to heat illness is related to a number of factors including underlying medical conditions (e.g., thyroid disease) which may influence the normal thermoregulatory mechanisms, certain medications, individual sweat rates, and acclimatization to the ambient temperatures.
 

Arnold M. Ramirez, M.D.
Director, Bayfront Sports Medicine Fellowship
Affiliate Assistant Professor, University of South Florida College of Medicine
Clinical Associate Professor, Florida State University College of Medicine

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date: September 17, 2008