Nieman, David C. Dr.PH, FACSM
Q: I exercise vigorously for 1 to 2 hours a day, sweat a lot, and often notice salt residue on my skin after I have cooled down. Do I need to ingest salt tablets to replace the salt I lose in sweat?
A: No, you do not need to ingest salt tablets, although you train up to 2 hours a day. Yes, it is true that your sweat has salt in it, approximately ¼ to ½ teaspoon per quart. However, even if you sweat approximately 1 to 2 quarts per hour of exercise, the salt lost from your body is easily replaced from the diet and sports drinks (1,2). Also, if you train hard on a regular basis, you are unlikely to develop a salt deficiency even with high sweat rates on hot days because training promotes changes in your body that conserve salt.
Some athletes, however, need to be concerned about adequate salt intake. American football athletes, for example, can lose 10 quarts of sweat a day during twice-a-day practice sessions (3). Ultramarathon athletes can sweat out gallons of body water during prolonged race events. The danger for these athletes is low body sodium levels (i.e., hyponatremia) (4,5). If water or other low-sodium beverages are consumed in high amounts, the loss of sodium in the sweat causes the sodium level in the blood to fall too low, causing symptoms similar to heat illness. These symptoms include fatigue, light-headedness, weakness, cramping, weight gain, nausea, bloating and/or swelling, dizziness, headache, confusion, fainting, disorientation, and seizures or coma (severe cases).
To prevent hyponatremia, ultra-athletes and football players should avoid overdrinking water relative to the sweat rate, obtain body weights every 1 to 2 hours and then adjust beverage intake to maintain weight, and use sports drinks that contain sodium (4,5). But let me emphasize that for you and most other hard-core fitness enthusiasts, hyponatremia is not a concern.
If loss of body sodium is not an issue for most exercisers, then why, you may ask, do sports drinks contain sodium? The addition of small amounts of sodium to a sports beverage enhances palatability, helping individuals take in more fluids during and after workouts (6). Also, beverages with sodium in them lead to less urination than plain water and counter the drop in water from the blood compartment during exercise. However, sodium from sports drinks does not enhance intestinal fluid absorption in most people with an adequate dietary intake or improve endurance performance. The American College of Sports Medicine recommends that 0.5 to 0.7 g of sodium be added to each liter of sports drink (6).
As I am sure you are aware, the issue for most adults is excessive diet salt intake. Salt or sodium chloride is 40% sodium. One teaspoon of salt weighs approximately 5,000 mg and has 2,000 mg of sodium. Sodium is an essential mineral that plays a role in the regulation of water balance, normal muscle tone, acid-base balance, and the conduction of nerve impulses. Your body needs approximately 500 mg of sodium per day, but most Americans consume much more-approximately 4,000 to 6,000 mg per day or more than double the recommended amount.
High sodium intake is associated with high blood pressure, a form of cardiovascular disease and a key risk factor for myocardial infarction and strokes. High blood pressure (i.e., a systolic blood pressure of 140 mmHg or higher or a diastolic blood pressure of 90 mmHg or higher) is a major health concern and is now found among 26% of all American adults. Another 31% have prehypertension, defined as a systolic blood pressure ranging from 120 to 139 mmHg or a diastolic blood pressure of 80 to 89 mmHg.
The Dietary Guidelines for Americans from the United States Department of Agriculture recommends that to prevent disease, sodium intake for young adults should be limited to no more than 2,300 mg per day, the equivalent of a little more than a teaspoon of table salt (7). Older individuals, African Americans, and people with chronic diseases including hypertension, diabetes, and kidney disease are especially sensitive to the blood pressure-raising effects of sodium and should consume less than 1,500 mg of sodium per day.
Where are we getting all that sodium? Small amounts of sodium occur naturally in foods, and many people add salt to their food at the table. However, most of the salt consumed, approximately 77% of total intake, comes from processed foods and foods eaten outside the home in restaurants. The richest sources of sodium are sauces, salad dressings, cheeses, processed meats, soups, and grain-cereal products. The food label identifies the sodium content of packaged foods.
Many processed foods contain shockingly high levels of sodium. For example, several types of Swanson Hungry Man frozen dinners contain more than 3,000 mg of sodium, more than a person should eat in an entire day. A one-cup serving of Bush's Best Homestyle Chili Original contains 1,380 mg of sodium. A package of Maruchan Instant Lunch Ramen Noodles with Vegetables provides 1,410 mg of sodium. Many other processed foods contain 500 to 1,000 mg per serving. Many restaurant foods and meals contain extremely high levels of sodium. A typical Reuben sandwich has 3,270 mg of sodium, and cheese fries with ranch dressing has almost 5,000 mg of sodium.
For most people, even fitness enthusiasts, the issue is too much sodium, not a deficiency. There are several steps you can take to keep your sodium intake at healthy levels:
* Learn to read food labels, and limit foods high in sodium. Look for labels that say "low-sodium"-they contain 140 mg or less of sodium per serving.
* Choose more fresh fruits and vegetables (which are very low in sodium).
* Choose fresh or frozen fish, shellfish, poultry, and meat most often. They are lower in salt than most canned and processed forms.
* Reduce the use of salt during cooking, and use herbs, spices, and low-sodium seasonings instead. Excellent salt substitutes are any of the Mrs. Dash Seasonings, Schilling Salt-Free Seasonings, or Parsley Patch Seasonings.
* Avoid using the salt shaker on prepared foods at the table, and go easy on condiments such as soy sauce, ketchup, mustard, pickles, and olives.
* Limit the use of foods with visible salt on them (snack chips, salted nuts, crackers, etc.).
Exercising hard each day and sweating salt out of your body is a good practice. Don't counter this benefit by eating salt tablets. Instead, follow the low-sodium guidelines outlined in this article, and you will improve your odds of avoiding high blood pressure later on in life.
1. Shirreffs, S.M., L.E. Armstrong, and S.N. Cheuvront. Fluid and electrolyte needs for preparation and recovery from training and competition. Journal of Sports Sciences
2. Sharp, R.L. Role of sodium in fluid homeostasis with exercise. Journal of the American College of Nutrition
25(3 suppl):231S-239S, 2006.
3. Godek, S.F., A.R. Bartolozzi, and J.J. Godek. Sweat rate and fluid turnover in American football players compared with runners in a hot and humid environment. British Journal of Sports Medicine
4. Montain, S.J., S.N. Cheuvront, and M.N. Sawka. Exercise associated hyponatremia: quantitative analysis to understand the etiology. British Journal of Sports Medicine
5. Von Duvillard, S.P., W.A. Braun, M. Markofski, et al. Fluids and hydration in prolonged endurance performance. Nutrition
6. American College of Sports Medicine. Position stand on exercise and fluid replacement. Medicine & Science in Sports & Exercise®
7. U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans
(6th ed). Washington, DC: U.S. Government Printing Office, 2005.