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How much liquid should I drink daily?

Asked by Brooke, North Carolina

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I drink about 6 to 10 ounces of fluids per day and I am 15. I know that's really bad, but on top of that I am training for a half-marathon and I've run up to 12 miles. On days like that, I still lack adequate liquids. Will this pose any problems in the near or far future other than dehydration, which I have yet to experience?

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Living Well Expert Dr. Jennifer Shu Pediatrician,
Children's Medical Group

Expert answer

Thanks for your question. It's great that you're training for a half-marathon and that you haven't had trouble with dehydration. However, there are a number of reasons why you should make sure you get enough fluids, especially with strenuous exercise, keeping in mind that some of your fluid intake will come in the form of foods rich in water (such as fruits, vegetables, yogurt, etc.).

Although you may not feel dehydrated, not getting enough liquid can lead to performance problems such as not being able to run as far or as fast as you would expect. Dehydration may cause fatigue and fainting in addition to electrolyte imbalances, heat-related illnesses (such as cramps, heat exhaustion and heat stroke), a condition called rhabdomyolysis (which involves muscle breakdown and the release of muscle enzymes into the body), kidney failure and shock.

It's important to note that people lose water during exercise (through sweat and from more rapid breathing than at rest) at different rates so there's no set amount that everyone needs for a half-marathon. One way to determine how much fluid you specifically need during a long run is to weigh yourself before and after one session and figure out how much "water weight" you lost. It's easiest to do this in kilograms (divide your weight in pounds by 2.2). For each kilogram lost during exercise you will need a liter of fluid. Add to that any fluid that you drank during the training in addition to the amount of fluid you urinated (if you want to be exact). The next time you run that distance, plan to drink the total amount of fluid that you calculated over the course of the training.

Finally, it's crucial to avoid drinking too much fluid, especially during extreme exercise, because this can lead to a serious condition called hyponatremia, in which a low sodium level in the body may cause nausea, vomiting, weakness, headaches, seizures and possibly even death.

For more information, I encourage you to consult with your physician or another authority who is knowledgeable in sports training. Good luck!

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