When we think of hydration, we may think of water - HOWEVER - just as important is what else is lost when we sweat.
Sweat is the combination of water and electrolytes, including sodium, potassium, calcium, chlorine, phosphate, and magnesium. It is important that you have the correct balance of these minerals in your body fluids in order to maintain healthy blood chemistry and to facilitate many physiological processes. Sweating without properly rehydrating can cause electrolyte imbalances. Not regularly replacing lost water and electrolytes can result in dehydration, impairing physical and mental performance. Over-hydrating without including electrolytes can also disrupt the blood-chemistry balance.
"It should be emphasized that sweat losses can exceed 1.5 liters/hour when working in very hot environmental conditions," as reported in a study by the Curtin University of Technology's School of Public Health and published in the Journal of Journal of Occupational Medicine and Toxicology. In this sweat is sodium, which can be lost at more than 10 grams per working day, the amount found in 25 grams of salt, as reported in the study. (Remember, salt is the combination of sodium and chloride.) That means a person working in the heat, and who has not yet acclimatized to the higher temperatures, can lose 10 to 12 liters of water and more than 4 teaspoons of salt, since there are six grams of salt in a teaspoon.
Unless you are tested in a controlled environment, there is no way to determine how much sodium you expel from your body in the form of sweat. The study did find that the subjects working at a moderate pace (40% of VO2max) for a 10-hour shift in 95-degree Fahrenheit heat lost between 4.8 grams and six grams of sodium - what is found in almost two to 2.5 teaspoons of salt.
According to the American Heart Association, there are 2,300mg of sodium in one teaspoon of salt. Although the association recommends limiting your daily sodium intake to 1,500 mg of sodium a day, it is important to take into account what you may expend in your daily activity. A sedentary person may want to follow the AHA guidelines; however, a person who is more active or who is exposed to the heat and who has a higher sweat rate would more than likely lose more water and electrolytes, including sodium. This is especially true when you are trying to become used to hotter temperatures.
Interestingly, there was no significant correlation between sweat rate or sodium concentration of the sweat and the subjects' fitness levels, ages, or body compositions. Researchers state that your sweat rate and the concentration of sodium in your sweat has more to do with genetics than with lifestyle.
According to the study, it takes about 10 days of heat exposure for the body to become well acclimatized to the summer heat if coming from cooler spring and winter temperatures. Once your body is used to the heat; however, your body has the ability to quickly adapt to changes in the temperature by self-regulating sodium secreted through sweat. This is your body's self-preservation response.
After learning about water and sodium loss, what can we do to protect our loved ones and ourselves when working or playing in the heat, especially when our bodies are trying to become used to the higher temperatures? Researchers of the study recommend not relying on sports drinks and other beverages with high sugar content but rather on sports beverages with reduced sugar or diluting your sports beverage with water.
People working in the heat and who are drinking plain water throughout the day should make sure to have meal breaks during their shifts since nearly all foods contain sodium and other nutrients that allow for proper hydration levels. Those working in harsh heat conditions may have to eat sodium-rich foods during their meal breaks.
Give yourself about 10 days to become acclimated to higher temperatures before pushing yourself in the heat. Above all, listen to your body and drink at regular intervals throughout the day. Remember, it is not just about the fluid you replace, it is about the electrolytes as well, especially sodium. If you are concerned about your hydration levels and whether or not you are properly replenishing the water and electrolytes lost, consult your physician.
Tracey Carlton is a Fitness Nutrition Specialist and Personal Trainer certified through the International Sports Sciences Association and American Fitness Institute, and is the owner of On-Point Nutrition, which offers both online and face-to-face nutrition and fitness coaching to meet your individual weight, performance, and health goals. She also is employed by the Greater West Point Family YMCA. Feel free to e-mail your questions or nutrition topics of interest to firstname.lastname@example.org. You can find On-Point Nutrition on Facebook or at http://www.on-pointnutrition.com.