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ACSM'S Health & Fitness Journal:
doi: 10.1249/01.FIT.0000257711.99739.26
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A Nutritionist's View: Sodium and Fluid Needs for Athletes

Volpe, Stella Lucia Ph.D., R.D., LDN, FACSM

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Stella Lucia Volpe, Ph.D., R.D., LDN, FACSM, is an associate professor and the Miriam Stirl Term Endowed Chair in Nutrition in the Division of Biobehavioral and Health Sciences at the University of Pennsylvania, Philadelphia, PA. Dr. Volpe is a member of the Gatorade Sports Nutrition Board. Her degrees are both in Nutrition and Exercise Physiology, and Dr. Volpe also is ACSM Exercise Specialist® certified. Dr. Volpe's research focuses on obesity and diabetes prevention, using traditional interventions, mineral supplementation, and more recently, by altering the environment to result in greater physical activity and healthy eating. Dr. Volpe is an associate editor of ACSM's Health & Fitness Journal®.

There is so much talk about lowering people's salt intake, and for good reason-many people in the United States have hypertension (or high blood pressure), which has been called the silent killer. It causes a large number of cerebrovascular accidents (strokes) each year, and lowering salt intake can help many people to lower their blood pressure. On the other extreme, however, are athletes, who need more salt to remain well hydrated and to optimize their exercise performance. Unless there is a contraindication to increasing salt intake, most athletes should be somewhat liberal about consuming salty foods and/or using the salt shaker at the table or while cooking. Sodium (Na+) is lost in sweat and needs to be replaced. Salt (sodium chloride [Na+Cl-]) is an easy way for an athlete to increase his/her sodium intake. Although many Americans take in more salt than is recommended by the Dietary Reference Intakes (established as Adequate Intakes [AI], which range from 1,000 to 1,500 mg of sodium per day, depending on the person's age and sex, with a tolerable upper intake level [UL] established at no more than 2,300 mg of sodium per day), athletes typically require more than the UL for sodium, particularly if they live in hot and humid environments, and/or train and compete in ultraendurance events (1). Increased salt intake also is important for people who have very salty sweat. The way this can be determined is by viewing the amount of salt on clothing or hats after an athlete trains or competes. Any visible whiteness on clothing or hats is salt, in which case, it is even more important for that athlete to consume more salt in his/her diet.

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Why Is Salt Intake Important for Athletes?

As stated previously, increased salt intake can help prevent dehydration. In addition, increased salt intake can prevent hyponatremia from occurring. Hyponatremia literally means low sodium in the blood. Hyponatremia has become more prevalent among ultraendurance athletes and/or those who are slower finishers in events (e.g., more than 4 hours in a marathon or in events that last greater than 4 hours) who consume only water during their events. Normal blood sodium levels are between 135 to 145 mill-Equivalents per liter (mEq/L). If the athlete's blood levels fall below that, hyponatremia ensues. Some of the signs and symptoms of hyponatremia include dehydration, headache, vomiting, restlessness, undue fatigue, disorientation, slurred speech, confusion, moderate to severe muscle cramps, seizures, and coma, which can ultimately lead to death. It is important for athletes to realize that water alone during events greater than 1 hour is not sufficient for rehydration, and can even lead to hyponatremia. Sports drinks with the proper percentage of sodium, potassium, and glucose are the best choices for longer events. These sports drinks help not only to hydrate the athlete, but provide the sodium needed to maintain normal sodium levels in the blood, which can help prevent hyponatremia. Hyponatremia does not occur frequently but can occur in individuals who may have an underlying (known or unknown) kidney problem.

It has been shown that endurance and ultraendurance athletes can lose from 1 to 3 g of salt per liter of sweat. Depending on an athlete's sweat rate, the heat and humidity, and the actual type of training, an athlete can lose a liter or more of sweat per hour. This could result in a large amount of sodium lost from the blood if the athlete does not properly hydrate before, during, and after the training session or event.

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Although proper nutrition and hydration should occur at all times, athletes may not always be thinking about sodium intake at each meal. They should, however, be encouraged to eat saltier foods throughout the day, as well as to properly hydrate themselves before, during, and after practice, preferably with a sports drink (especially if they are training for more than 1 hour). Pretzels are an easy food to carry around and provide added salt for athletes (see Table for additional examples.)

Table. Examples of S...
Table. Examples of S...
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There are many things an athlete can do to prevent hyponatremia. Some have already been mentioned and include the following:

1. Drinking a sports drink that contains sodium.

2. Eating saltier foods and being liberal with salting foods (unless there is a contraindication in doing so).

3. Hydrating properly.

4. Monitoring urine color. Although this is a crude measure of hydration status, it does not require laboratory equipment and is easy to do. A pale yellow color usually means that a person is hydrated well. If the athlete's urine is a dark yellow color, he/she is not properly hydrated. Note, however, that vitamin/mineral supplements will make urine a bright yellow color. Thus, it is important to know if an athlete is taking supplements. It is also important to note that, to obtain the most accurate reading, it is best to use either first-morning-urine samples, or samples after several hours of stable hydration status.

5. Obtaining body weight before and after practice will ascertain if the athlete is properly hydrating himself/herself. A weight loss of two pounds or more indicates improper hydration.

6. Avoiding the use of aspirin and other nonsteroidal anti-inflammatory medications. These medications can increase the risk of hyponatremia in athletes and should be avoided, especially during major events.

It is always important for an athlete to remember to seek advice from a physician, exercise physiologist, and/or registered dietitian (who also is certified as a sports nutritionist) if he/she has any questions or medical problems related to salt intake and exercise performance and health. The author refers the reader to the list of references and Web sites that will provide more detailed information on how to prevent hyponatremia.

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Summary

Sodium is an important part of any athlete's diet because it helps to maintain proper hydration and prevent hyponatremia. Increasing salt intake is especially important for salty sweaters and for people who exercise in hot/humid environments for long durations. Consuming sports drinks that contain sodium is a good way for athletes to hydrate themselves and provide the proper sodium needed for replenishing the sodium losses in sweat. Eating foods that are saltier also will help with hydration and overall performance.

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Recommended Readings

Denny, S. What are the guidelines for prevention of hyponatremia in individuals training for endurance sports, as well as other physically active adults? Journal of the American Dietetic Association 105(8):1323, 2005.

Eichner, E.R., E. Nadel, R. Laird, et al. Hyponatremia in sport: symptoms and prevention. Sports Science Exchange 12(4):2, 1993. Available at: http://www.gssiweb.org/reflib/refs/51/d0000000200000043.cfm?pid=60&CFID=4514282&CFTOKEN=23752796. Accessed September 18, 2006.

O'Connor, R.E. Exercise-induced hyponatremia: causes, risks, prevention, and management. Cleveland Clinic Journal of Medicine 73(Suppl 3):S13-S18, 2006.

Speedy, D.B., I.R. Rogers, T.D. Noakes, et al. Diagnosis and prevention of hyponatremia atan ultradistance triathlon. Clinical Journal of Sport Medicine 10(1):52-58, 2000.

Vlach, S.M. Facts on hyponatremia. Available at: http://www.honoluluclub.com/pulse.php?ID=31. Accessed September 18, 2006.

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References

1. Food and Nutrition Board, Institute of Medicine of the National Academies. Dietary Reference Intakes for Water,Potassium, Sodium, Chloride, and Sulfate. The National Academy Press: Washington, DC, 2005.

2. Montain, S.J., S.N. Cheuvront, and M.N. Sawka. Exercise-associated hyponatremia: quantitative analysis for understanding the aetiology. Br. J. Sports Med. 40:98-106, 2006.

© 2007 American College of Sports Medicine

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