Skip to content
Dehydration in the hot months to come
Rich Weil, MEd, CDE posted:
Hi Everyone,

The weather is going to start getting hot and one of the key factors in promoting good health and fitness is to focus on hydration status, especially for people who work out regularly, and especially so for people who live at high altitude and for people who exercise in hot, humid environments. The risks of dehydration can be quite severe. It can:

1. lead to cramps, heat exhaustion, and even heatstroke, which can be fatal.

2. cause stress on the kidneys (particularly unhealthy kidneys),

3. decrease in blood volume which can lower blood pressure and decrease oxygen levels in tissue so low that death can occur in just a few minutes

4. coma

A number of physiological factors contribute to dehydration. For instance,

1. your body can absorb about 24 to 32 ounces of water an hour (if you drink more than that it doesn't get absorbed), but you could easily lose twice that much in hot weather which means you can't keep up with the fluid loss, which means the longer you exercise the more likely you are to become dehydrated. (A professional baseball pitcher can lose up to 10 pounds of water from sweat after pitching nine innings on a hot summer day!).

2. by the time you are thirsty there is the risk that you are already dehydrated

Continued in the next message
Rich Weil, MEd, CDE responded:
Preventing Dehydration

Preventing dehydration isn't difficult to do. Below are guidelines for hydration from the National Athletic Trainers' Association, and below that are resources for you to read more.

Here are hydration guidelines:

1. Drink 17 to 20 fl oz of water or a sports drink 2 to 3 hours before exercise and 7 to 10 ounces of water or a sports drink 10 to 20 minutes before exercise. Remember, by the time you are thirsty you may already be dehydrated, so don't wait for thirst before you drink.

2. During exercise fluid replacement should approximate sweat and urine losses and at least maintain hydration at less than 2% body weight reduction. This generally requires 7 to 10 ounces every 10 to 20 minutes during exercise. More than 2% loss of body weight can affect performance, particularly endurance performance, although not for all individuals. Weigh yourself nude before and after exercise to get an idea of how much fluid you lose.

3. Carbohydrate (CHO) concentrations greater than 8% increase the rate of CHO delivery to the body but compromise the rate of fluid emptying from the stomach and absorbed from the intestine. Fruit juices, CHO gels, sodas, and some sports drinks have CHO concentrations greater than 8% and are not recommended during an exercise session as the sole beverage.

4. Post-exercise hydration should aim to correct any fluid loss accumulated during exercise. Rehydration should contain water to restore hydration status, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration.

5. Include CHOs in the rehydration beverage during exercise if the session lasts longer than 45 to 50 minutes or is intense. Drinking 1 liter of a 6% CHO drink per hour of exercise will be adequate.

6. Inclusion of sodium chloride in fluid-replacement beverages should be considered under the following conditions:

a. inadequate access to meals or meals not eaten;

b. physical activity exceeding 4 hours in duration;

c. during the initial days of hot weather.

d. under these conditions, adding modest amounts of salt (0.3 to
0.7 g/L) can offset salt loss in sweat and minimize medical events associated with electrolyte imbalances (eg, muscle cramps, hyponatremia). Adding a modest amount of salt (0.3 to 0.7 g/L) to all hydration beverages would be acceptable to stimulate thirst, increase voluntary fluid intake, and decrease the risk of hyponatremia (low sodium levels) and should cause no harm.
Rich Weil, MEd, CDE replied to Rich Weil, MEd, CDE's response:

Exercise-induced hyponatremia is the loss of sodium in the body to levels lower than normal due to over consumption of water. Over consumption of fluid is when you drink more than you lose in sweat and urine. Hyponatremia is a condition that can lead to cardiac events and even death. It became a big issue about 20 years ago when marathon runners, encouraged to drink at every water station, presented at the finish line with symptoms that looked like dehydration (hyponatremia and dehydration have similar symptoms). They were immediately escorted to the medical tent where they were given intravenous fluids.It tunrs out they were not dehydrated, but rather they were hyponatremia. The IV fluids, unfortunately, lowered their sodium levels even more, and this lead to a number of deaths. The problem was a new one and it prompted sports medicine physicians to re-consider fluid intake guidelines for athletic events. Here is a link to a consensus statement on hyponatremia

To prevent hyponatremia you should weigh yourself before and after a workout. If you weigh more than you did before the workout than you know you are drinking too much and should cut back.

Here are hydration resources:,7120,s6-242-302--10085-1-1X2-3,00.html #

Good luck with your spring and summer training, and be sure to stay healthy!
Rich Weil, MEd, CDE replied to Rich Weil, MEd, CDE's response:
One final point

Everyone responds differently and so hydration guidelines should be individualized for each person. The goal is to prevent excessive weight loss (>2% of body weight). You can lose anywhere from approximately .4 to 1.8 liters per hour depending on the amount of exercise, temperature and humidity, and your body weight, and so the prevent dehydration you should follow the guidelines above, and as I mentioned already, weigh yourself before and after exercise (nude if possible) to see how much fluid you lose. One liter of water weighs 2.25 pounds, and so you can replace fluid after exercise based on how much weight (from fluid) you lost. For example, if you lose one pound you can replace it by drinking about half a liter. Again, enjoy your training and stay safe!
mook6877 replied to Rich Weil, MEd, CDE's response:
i am about to play in a golf tournament in palm springs. i have done this the past 2 years. on the first day of the tournament i always end up getting really really sick from the heat but the next day i am absolutely fine. my neck gets stiff and sore, i feel like i will pass out and no matter how much fluid i drink(and it is a lot) i still get this way. i do not get this at all the next 3 days. is there any way to prepare myself before i get there so im not so bothered by the heat? it usually takes me a few hours after the sick feeling to get any better. of course when it does go away i feel like a champ.
Rich Weil, MEd, CDE replied to mook6877's response:
Prepare several days ahead of time by increasing consumption of water and following the guidelines above for increasing use of salt. It takes a few days to acclimate to heat, so if you are really serious about this, then you ought to go there a few days before. That's the best solution.
2luvtwins replied to Rich Weil, MEd, CDE's response:
Thank you for this information. I am printing it out and giving this to my 13 year old daughter who has been exercising with me and 2 times a week we run outside. She has been having a difficult time and getting sick to her stomach and very red to her face, even feeling faint at times. I know they are hard headed at this age, but she blows me off when I tell her these things could be happening because she is NOT drinking enough water during the day. She will be out in the heat ALL summer long, she will be playing in a summer program with high schoolers. And it's not even 100 degrees here yet. I'm worried about her and I'm trying to convince her of this.

Hopefully your words will help.
Rich Weil, MEd, CDE replied to 2luvtwins's response:
You're welcome. Tell her she'll run better if she drinks (if that will help at all), and I suggest you contact the director of the program she's involved in and check about how they plan to handle hydration and water breaks, etc. Sometimes adults in charge don't know what the right thing to do is. It's your right to make sure they do.
2luvtwins replied to Rich Weil, MEd, CDE's response:
thank you. I'm lucky, while she is away at softball camp I have an insider that knows whats going on and said she will definatley keep an eye on her. I've talked to the coach alot and he seems to really care about these girls and their well being. I'm sending her with a ton of water for that week. Plus for the rest of the summer I will do whatever I have to make sure she is hydrated. I'm told that he makes sure they take their water breaks. We shall see how this goes. Can't wait for the hard headiness to go away (don't know if that's a word or not) ha ha
Rich Weil, MEd, CDE replied to 2luvtwins's response:
You're welcome.
DeadManWalking56 responded:

Dr. Weil:

Salt loss is huge in heat related problems. People need to get more potassium when training or exercising in the heat.

Keep oranges or bananas on hand, along with water. I've always been a big OJ fan, and have also had better heat tolerance than most people I know.

Helpful Tips

Water aerobics
Water aerobics does not put the stress on your knees, ankles and/or back. More
Was this Helpful?
23 of 23 found this helpful

Related Drug Reviews

  • Drug Name User Reviews

Report Problems With Your Medications to the FDA

FDAYou are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.