Updated: Aug 6, 2022
It't hot out.
You are sweating a lot.
You drink a lot more water.
You might even try sports drinks. They have electrolytes - right?
You think all this drinking will cool you down. It doesn't.
But we have been conditioned to think it will. So, we drink more.
Too much water or sports drinks too quickly can become deadly. Sometimes it's called water intoxication. It's also call hyponatremia which means low salt.
Basically, the salt in your body gets diluted from all the extra water or sports drinks you drink. This causes lots of problems including brain swelling. This can kill you.
Your Body Temperature
You are usually good at keeping your body temperature under control. When you get too hot you feel fatigued. You slow down. Your muscle stop generating extra heat. You sweat. If it's not too humid, the sweat evaporates. The evaporation cools you. The sweat drips off your body and cools you. Your body temperature returns to normal. No problems.
You Body Will Adjust to the Hot Weather
It takes about 2 weeks of activity in the heat for your body to adjust to hot weather. You will sweat more. Your body adds more blood to carry heat to your skin. The extra skin heat causes more evaporation. With the extra blood your brain and organs stay supplied while heat is carried to your skin. You won't pass out or feel sick.
Slowly Increase Activity Levels in the Heat
If you slowly increase your activity level over a 2 or 3 week period in the heat you will be a lot better off. The trick seems to be to gradually get to the activity intensity you want in the heat. This gives your body time to increase the amount of blood and your sweat rate.
Drinking Extra Water Doesn't Cause Extra Cooling
When you sweat you lose water. You know when you sweat it cools you. So, it makes sense to replace the water you lose. Right? Yes - but it doesn't make sense to drink "extra" water or sports drinks. Drinking extra water will not cool you more. Replacing water you lose will let you keep sweating to cool yourself.
All the experts agree you should drink to replace the water your lose, so you body can continue to control your temperature. The experts don't seem to agree on how much or when to drink. Some say you should drink to satisfy your thirst, and maybe a little more. Others say you should drink every hour - thirsty or not.
"Drink to Thirst" Experts
For thousands of years, people have been active during the heat of the day while drinking little. They drank at the end of the day to replace the fluid they lost.
Drink to Thirst" experts talk about marathon race winners. Even in hot and humid weather the fastest runners don't stop to drink during the race. These winners - the fastest runners - are the most dehydrated at the end of the race.
These experts stress the high rate of hyponatremia in runners that follow the "drink every hour" guidelines. In the 2002 Boston Marathon, 13% of the runners had hyponatremia. Most were following the "drink every hour" guidelines.
Finally, the "drink to thirst" experts point to their research showing that almost all documented heat-related deaths of runners are caused by drugs. And, the winners of marathon races in hot and humid weather often have the highest body temperatures and are fine.
Dr. Tim Noakes is one of the leading "drink to thirst" experts. His book, Waterlogged, lays out the case for drinking to satisfy thirst.
"Drink Every Hour" Experts
The "drink regularly, thirsty or not" experts recommend the opposite. They say heat illnesses are prevented by their guidelines, and performance is improved. The Drink to Thirst experts done agree. The Drink to Thirst experts stress that these guidelines are the result of lab experiments, not real world - real race conditions. This 2016 article by Elizabeth Quinn on verywellfit outlines the drink thirsty or not guidelines.
Get Ready for Activity in the Heat
Make sure you drink enough to replace the fluid you lose
If it is hotter than you are used to, reduce your activity level.
Prepare yourself for new activities or more intense activities in hot weather. Slowly increase the activity level over at least 2 weeks in the heat.
Christopher DiPasquale, PhD, PT, OCS, SCS, CHT is a physical therapist at Performance Physical Therapy & Sports Medicine, with offices in Hebron and Colchester, Connecticut. He is board certified by the American Board of Physical Therapy Specialties in Orthopedic Physical Therapy and Sports Physical Therapy and a Certified Hand Therapist by the Hand Therapy Certification Committee. Visit pptsm.com for more information.