Summer, Sweat and SaltBy Cathy Feiseler, MD Summer is here with all of its heat and humidity. Stories about heat stroke and dehydration are in the news. Then, in contrast, you hear a story about a runner who became hyponatremic (low sodium in the blood) and died from drinking too much water. What's a runner to do? For years you have heard that it is important to remain well hydrated, especially during exercise. Dehydration impairs the function of all body systems, putting the runner at risk for problems ranging from poor performance to heat stroke and death. Water is a great fluid replacement drink … to a point. It is possible to drink too much water and basically dilute the body's levels of electrolytes, especially sodium. This said, it is important to remember that dehydration is a much more common occurrence. Thirst is a poor indicator of hydration status; you may be 1-2% dehydrated before you experience thirst. So, what are you supposed to drink? When you are not exercising, water is fine. During exercise lasting less than 60 minutes, water is a suitable drink. Longer runs are when things get somewhat unpredictable. People sweat at different rates, ranging from a half quart up to 4 quarts of fluid lost per hour. Several factors determine rate of sweat. Some people have more sweat glands, so they produce more of this fluid. Heat and humidity greatly affect the rate at which sweat is produced. Level of fitness also plays a role; as the body adapts to exercise, especially in a warmer environment, it produces greater quantities of sweat during exercise, as an adaptive response to the heat that is produced by the exertion. How do you figure out how much sweat you produce? Weigh yourself before and after a run. Each pound that you have lost represents a fluid deficit of 16 ounces. If you ran for 30 minutes and lost 1 pound, you can work on the premise that you lose about a quart (32 ounces) of fluid each hour. Plan on drinking an adequate amount of fluid during longer runs to account for this. This is a rough guide, since the weather, especially humidity, will affect the rate of sweat production on any given day, but it should put you in the right ballpark. The concentration of sodium is also extremely variable. Often, as the body adapts to exercise in the heat, the body produces greater quantities of less concentrated sweat. Despite this adaptive response, some people seem to produce salty sweat. Their shorts and skin are crusted in white following a workout. So what is an appropriate replacement drink … sweat? There are a number of sports drinks on the market that contain electrolytes (e.g. Gatorade, POWERAde, AllSport). These drinks also contain carbohydrates in a 4-8% concentration to improve taste and supplement the decreasing supply of this energy source in your body during exercise. Replacing carbohydrates becomes increasingly important as running exceeds 60 minutes. The concentration of carbohydrates in the sports drinks does not compromise the absorption of fluids in the gastrointestinal system. More concentrated sources of carbohydrates, such as orange juice, will slow the absorption process. What about all of the other additives in some sports drinks? A combination of carbohydrates and protein in a 4:1 ratio (like Accelerade) has shown promise in improving endurance when compared with carbohydrate only drinks. The protein stimulates insulin, which is involved in the transport of energy into muscle and in the conversion of glucose into its storage form, glycogen. Carbohydrates stimulate insulin, but ingestion of increased amounts will decrease absorption of fluids from the gastrointestinal tract. The addition of protein enhances the effects of insulin, according to several studies. Vitamins and minerals have been added to some sports drinks. Unless your diet is deficient in these substances, they probably do not improve performance. The amounts of these substances in sports drinks do not cause any problems. Some drinks contain supplements; typically, the amounts present are lower than the doses recommended to achieve their purported effects. Be careful with supplements; not all of them are safe (for example, recent concerns about liver failure with use of kava-kava). Research these substances before you consider using any of them. Enjoy your summer running by staying well hydrated. Find a drink that works well for you and drink up. Warning signs of dehydration Symptoms of Hyponatremia (listed from least to most severe) Dr. Cathy Fieseler is the RRCA Sports
Medicine Committee chairperson. If you have questions for Dr.
Fieseler you can write her at runmd@aol.com.
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