Electrolyte supplements are a varied group of prescription and nonprescription preparations used to correct imbalances in the body's electrolyte levels. Electrolytes themselves are substances that dissociate into ions (electrically charged atoms or atom groups) when they melt or are dissolved, thus serving to conduct electricity. In the human body, electrolytes are thus critical to the proper distribution of water, muscle contraction and expansion, transmission of nerve impulses, delivery of oxygen to body tissues, heart rate and rhythm, acid-base balance, and other important functions or conditions.
The ions that are formed when electrolytes are dissolved in body fluids are either positively or negatively charged. Positively charged ions are called cations, and are formed when an atom or atom group loses electrons. The most important cations in the human body are sodium, potassium, magnesium, and calcium ions. Negatively charged ions are called anions, and are formed when an atom or atom group gains electrons. The principal anions in the body include bicarbonate, chloride, phosphate, and sulfate ions, as well as ions formed by certain protein compounds or organic acids.
About 60 percent of an adult human male's total body weight is water. In adult women, the figure is about 55 percent, and is even lower in the elderly and in obese people. Two-thirds of total body water (TBW) lies inside cells and is known as intracellular fluid or ICF. The remaining third of TBW lies outside the cells and is called extracellular fluid or ECF. About 75 percent of ECF lies in connective tissue or the spaces between tissues outside the blood vessels (interstitial spaces), while the remaining 25 percent is within the blood vessels. In addition to representing different proportions of TBW, ICF and ECF differ significantly in their electrolyte content. Whereas the major cation in ICF is potassium, the most important cation in ECF is sodium. These differences in electrolyte levels help to regulate the movement of water between ICF and ECF.
Children are more vulnerable than adults to fluid and electrolyte imbalances, in part because they have different ratios of TBW to total body weight, and of ICF to ECF. A newborn baby carried to full term has a TBW ratio between 75 and 80 percent. The baby's total body water ratio decreases by 4-5 percent during the first week after birth and reaches the adult level of 60 percent by twelve months of age. Similarly, a newborn has an ICF: ECF ratio of 55: 45, which falls to the adult ratio of 70: 30 during the first year of life. In addition to these different fluid ratios, children's kidneys are less efficient than adults in regulating water balance; children have smaller organ systems that dissipate body heat less efficiently; and their core body temperature rises faster than that of an adult when they become dehydrated. All these factors help to explain why some electrolyte supplements are formulated specifically for children.
The purpose of electrolyte supplements is to restore the proper ratio of total body water to total body weight and the correct proportions of the various electrolytes in body fluids. Electrolyte imbalances may result from excessive intake or inadequate elimination of electrolytes on the one hand or by insufficient intake or excessive elimination on the other hand.
Body regulation of water and electrolytes
Under normal conditions, the water and electrolyte content of the body is regulated by the kidneys, the secretion of antidiuretic hormone, and the sensation of thirst. The average adult needs to take in about 700-800 mL (about 1.5-1.7 pints) of water per day in order to match the water lost through perspiration, breathing, and excretion of waste products. The water that is taken in by mouth is added to the 200-300 mL (0.42-0.63 pints) of water that are formed in the body each day through tissue breakdown.
The amount of water needed to match fluid losses, however, may be considerably greater than the average during exercise or in patients with fever, severe vomiting, or diarrhea. Adults with fever typically lose an additional .75-1.0 ounces of fluid per day for each degree that their temperature rises above normal. With regard to diarrhea, adults with cholera have been reported to lose as much as a quart of fluid per hour in their stools. The fluid lost in this way also contains sodium, potassium, and chloride, resulting in electrolyte imbalances in cholera patients as well as dehydration.
Exercise raises the total metabolism of the body to 5-15 times the resting rate. Most of this energy (70-90 percent) is released as heat, which is partially dissipated by the evaporation of sweat. Depending on weather conditions, the type and weight of clothing being worn, and the intensity of exercise or physical work performed, adults may lose anywhere from 1 to 2.5 quarts of fluid per hour through perspiration. Sweat, however, contains sodium chloride as well as smaller amounts of potassium, calcium, and magnesium. In order to maintain the proper balance of electrolytes in the body as well as fluid, athletes or people employed in outdoor work during warm weather may need to replace the electrolytes lost in sweat by taking capsules or drinking beverages containing supplemental electrolytes.
With regard to the sense of thirst, it is not always an accurate indication of the body's need for water. Researchers have found that many people do not feel thirsty until they have already lost about 2 percent of their total body weight through fluid losses. As a result, most people will not replace enough fluid during exercise or hot weather simply by drinking water until they no longer feel thirsty. In addition, the aging process, certain mental disorders, or drugs may affect a person's sense of thirst.
At the other extreme of water intake, a person may drink excessive amounts of water due to misunderstandings about their need for extra fluid during exercise. This condition is known as water intoxication or hyperhydration. It leads to abnormally low levels of sodium in the blood, a condition known as hyponatremia. Water intoxication may lead to swelling of the brain, confusion, disorientation, and eventually coma or death. Several marathon runners have died from water intoxication since 2002, as have teenagers who consumed large amounts of water after taking doses of Ecstasy (MDMA), a so-called "club drug." Other persons at risk for water intoxication include people with eating disorders and children with mental retardation. An important article published in the New England Journal of Medicine in April 2005 reported that as many as 13 percent of marathon runners developed hyponatremia during the course of a race as a result of dr! inking too much water, usually 3 quarts or more. Female athletes appear to be at greater risk of water intoxication and hyponatremia than male athletes.
Conditions associated with fluid and electrolyte imbalance
The most common conditions leading to fluid and electrolyte imbalance are as follows:
- Exposure to extended periods of extremely hot weather.
- High levels of athletic activity, military training, or outdoor work in such fields as construction, agriculture, forestry, fishing, and certain types of manufacturing.
- Extreme changes in diet.
- Reduced fluid intake.
- Medication side effects. Certain drugs, particularly diuretics, beta-blockers, and vasodilators, may increase the loss of electrolytes in urine and/or interfere with the body's ability to regulate its temperature during exercise or in hot weather.
- Severe illnesses characterized by high fever, recurrent diarrhea, and/or frequent vomiting. Such illnesses include cholera, viral gastroenteritis ("stomach flu"), shigellosis, and amebic dysentery.
- Severe burns covering more than 10 percent of the body.
- Surgical creation of a stoma or urinary diversion. These operations sometimes lead to an increased loss of body fluids while the patient's body is adjusting to the changes in urination and excretion resulting from the surgery. In addition, some forms of weight loss surgery intended to bypass parts of the small intestine in which food absorption occurs have a 70-percent rate of electrolyte imbalances as a complication of the operation.
- Diseases affecting the kidneys. These include diabetes mellitus, diabetes insipidus, and syndrome of inappropriate antidiuretic hormone secretion (SIADH) as well as cancer or infections of the kidneys.
- In infants, premature birth.
The various electrolyte supplements used in the United States and Canada as of 2005 are intended to prevent or treat electrolyte imbalances in very different situations or groups of patients. They range from sports drinks and other supplements used by amateur or professional athletes to prevent muscle cramps and improve athletic performance, to liquids used at home to prevent dehydration in children with diarrhea, to injections administered as part of enteral (feeding through a tube or stoma directly into the small intestine) or parenteral nutrition (intravenous feeding that bypasses the digestive tract).
The major categories of electrolyte supplements are as follows:
- Sports drinks. Sports drinks are beverages specially formulated to contain appropriate amounts of electrolytes and carbohydrates as well as water to replace the fluid and sodium lost through sweat during athletic activities. These beverages are popular with athletes at the college level, being used by about ¾ of the students on varsity teams at major universities. According to the American College of Sports Medicine as well as American and Canadian dietitians' associations, sports drinks are effective in supplying food energy for the muscles, maintaining proper levels of blood sugar, maintaining the proper functioning of the thirst mechanism, and lowering the risk of dehydration or hyponatremia. Other researchers have noted that the flavoring added to sports drinks encourages athletes to drink more during periods of exercise and thus maintain proper levels of hydration. Sports drinks can be purchased in supermarkets as well as health food stores; they include such well!-known beverages as Gatorade, Lucozade, Red Devil, Powerade, and Red Alert. Some of these popular supplements come in a semisolid form known as energy gels, some of which contain caffeine or various herbal compounds as well as carbohydrates and electrolytes.
- Over-the-counter powders and tablets. Some athletes—particularly those who participate in such sports as long-distance running or endurance cycling—prefer capsules or concentrated powders to maintain their electrolyte balance during exercise. The powders are mixed with 12 or 16 ounces of cold water prior to drinking, while the capsules can be taken before, during, and after exercise. Most contain flavorings to mask the naturally salty or bitter taste of the electrolytes themselves. Common brand names include eForce, NutriBiotic, and Endurolytes; prices range from $11 for 100 capsules to $35 for a 30-serving jar of powder. These products are regarded by the Food and Drug Administration (FDA) as dietary supplements.
- Over-the-counter electrolyte replenishers for children. As has been mentioned earlier, infants and young children are more vulnerable to dehydration than adults, particularly from severe gastroenteritis or diarrhea. A child may become dehydrated in less than a day from recurrent vomiting or episodes of diarrhea. Some doctors recommend that parents keep oral rehydration fluids containing mixtures of carbohydrates and electrolytes specially formulated for children in the medicine chest at home in case the child becomes dehydrated from a stomach virus or similar illness. Common brand names for these products, which are regulated by the FDA as "medical foods," include Pedialyte, Infalyte, Naturalyte, and Rehydralyte. Most come in a powdered form to be mixed with water as well as liquid forms; Pedialyte is also available as fruit-flavored freezer pops. Typical prices range from $6 for a box of 16 freezer pops to $34 for a quart of oral electrolyte solution.
- Oral rehydration formulae for children and adults. Oral rehydration salts, which are also known as ORS, have been a staple of treatment for cholera and other diseases accompanied by severe diarrhea in developing countries for almost half a century. First researched in the 1940s, oral rehydration salts were adopted by the World Health Organization (WHO) in 1978 in order to reduce the risk of death from dehydration caused by cholera-related diarrhea. Since the introduction of ORS, the number of children around the world who die from acute diarrhea has been reduced from 5 million per year to 1.3 million. Reformulated by WHO in 2002, the ORS salts come in packets to be kept in the home and mixed with water as soon as a child (or adult) falls ill. The new formula is a low-glucose and low-sodium mixture. If the WHO packets are unavailable, a comparable form of oral rehydration solution can be made by adding 8 tsp of table sugar, 1/2 tsp of salt, 1/2 tsp of baking soda (bicarbona! te of soda), and 1/3 tsp of potassium chloride to a liter (1.05 quarts) of water. In an emergency, a solution prepared from 1 tbsp of sugar and 1/2 tsp of salt added to 1 liter of water can be used to treat diarrhea.
- Multiple electrolyte injections. Various mixtures of electrolytes are available by prescription in injectable form to be added to enteral or parenteral nutrition formulae. These forms of feeding are used in patients who require supplementation or complete replacement of feeding by mouth, including patients with various intestinal disorders, AIDS, or severe burns. Basic solutions for total parenteral nutrition, or TPN, contain the electrolytes sodium, potassium, chloride, phosphate, and magnesium, although the exact proportion of electrolytes can be tailored to an individual patient's needs. Some injectable formulae contain dextrose, a sugar, and acetate or lactate as well as the five major electrolytes. Common brand names include Hyperlite, TPN Electrolytes, Lypholyte, Nutrilyte, Plasma-Lyte 148, and others. Some patients are taught to use these injectable formulae at home.
Recommended dosages for electrolyte supplements are as follows:
- Sports drinks. Since sports drinks and energy gels are not medications in the strict sense, the amount consumed will vary not only from person to person but also in a given individual from day to day depending on weather conditions, level of athletic conditioning, length of activity, and other factors. To lower the risk of dehydration in adults in hot weather, the American College of Sports Medicine recommends taking 20 ounces of a sports drink 2-3 hours before exercising; another 10 ounces 20 minutes before exercising; 10 ounces every 10-20 minutes during exercise; and 20 ounces per pound of weight lost during exercise after the activity is over. A group of researchers at Texas A & M University suggests that athletes competing in endurance events should drink about 500 mL (1 pint) of a sports drink containing 4-8 percent of carbohydrates and electrolytes 1-2 hours before an event. For events lasting longer than an hour, they should drink be! tween 600 and 1200 mL (1.25 to 2.5 pints) per hour of a sports drink containing carbohydrate plus 0.5-0.7 grams of sodium per quart.
- Over-the-counter powders and tablets. The usual recommended dose of powdered electrolytes is one scoopful (or prepackaged envelope) of powder dissolved in 12-16 ounces of water before exercising. Capsules may be taken as follows: 1-3 capsules 30-60 minutes before exercising; 1-6 capsules per hour during the workout; and 1-3 capsules after exercising.
- Over-the-counter electrolyte replenishers for children. Dosages for Pedialyte and similar oral rehydration solutions for children are usually based on the child's age and weight. The child's doctor should determine the quantity to be given if the child is younger than 12 months of age. Children between the ages of 1 and 2 years are usually given 34 mL of electrolyte solution per pound of body weight during the first eight hours of treatment and 75 mL per pound of body weight during the next 16 hours, although the doctor may adjust the dose if the child is very thirsty. Children between the ages of 2 and 10 are given 23 mL of electrolyte solution per pound of body weight for the first four to six hours of treatment, followed by 45 mL per pound taken over the next 18-24 hours. Freezer pops may be given to children older than 1 year as often as the child desires.
- Oral rehydration formulae. The WHO form of oral rehydration liquid is made by adding the full contents of one packet of powdered oral rehydration salts to a quart of drinking water. The solution should not be boiled. A fresh quart of solution should be mixed each day. Infants and young children should be given the solution in small amounts by spoon as often as possible. Adults and teenagers should take the WHO formula according to the doctor's directions.
- Multiple electrolyte injections. Basic TPN solutions are usually made up in liter batches and adjusted to each individual patient's needs. The standard adult dosage is 2 liters per day, usually administered by drip through a needle or catheter placed in the patient's vein for a 10-12-hour period once a day or 5 days per week. The patient may be given several units of premixed TPN fluid to store at home in the refrigerator or freezer. Each dose should be taken from the refrigerator 4-6 hours prior to use to allow it to warm to room temperature. TPN solution stored in a freezer should be moved to a refrigerator 24 hours before use.
Anion— An ion carrying a negative charge owing to a surplus of electrons. Anions in the body include bicarbonate, chloride, phosphate, sulfate, certain organic acids, and certain protein compounds.
Cation— An ion carrying a positive charge due to a loss of electrons. Cations in the body include sodium, potassium, magnesium, and calcium ions.
Cholera— A severe bacterial infection of the small intestine characterized by profuse diarrhea and eventual dehydration. Cholera is still a frequent cause of death among children in developing countries.
Electron— An elementary particle carrying a negative charge. Electrons may exist either independently or as components of an atom outside its nucleus.
Enteral nutrition— Nourishment given through a tube or stoma directly into the small intestine, thus bypassing the upper digestive tract.
Hyponatremia— Insufficient sodium in the blood.
Interstitial spaces— Spaces within body tissues that are outside the blood vessels. Interstitial spaces are also known as interstitial compartments.
Ion— An atom or group of atoms that acquires an electrical charge by the gain or loss of electrons.
Metabolism— The sum of an organism's physical and chemical processes that produce and maintain living tissue, and make energy available to the organism. Insulin resistance is a disorder of metabolism.
Parenteral nutrition— Nutrition supplied intravenously, thus bypassing the patient's digestive tract entirely.
Stoma— A surgical opening made in the abdominal wall to allow waste products to pass directly to the outside.
Water intoxication— A potentially life-threatening condition caused by drinking too much water, which leads to hyponatremia and may result in seizures, coma, and death.
- Sports drinks. Sports drinks should not be given to rehydrate children with vomiting or diarrhea, as they do not contain the proper balance of carbohydrates and electrolytes needed by children's bodies.
- Over-the-counter powders and tablets. These products should always be taken with adequate amounts of water and kept out of the reach of children.
- Over-the-counter electrolyte replenishers for children. These preparations should be stored out of the reach of children and away from heat and direct sunlight. In addition, they should not be given to patients with intestinal blockage.
- Oral rehydration formulae. WHO oral rehydration salts and packets of similar formulae should not be stored in damp places, as moisture can cause the contents to lose their effectiveness. These products should also be kept away from heat or direct sunlight. Unused oral rehydration solution should be discarded at the end of each day. As with electrolyte replenishers for children, oral rehydration formulae should not be given to patients with intestinal blockage.
- Multiple electrolyte injections. Patients using multiple electrolyte injections as part of total parenteral nutrition should have their blood and urine checked at regular intervals while they are receiving these medicines. They should also be taught to recognize the signs of infection at the injection site (pain, swelling, redness, or a cold sensation). In addition, these patients should not use sports drinks, other electrolyte supplements, or over-the-counter medications (including herbal preparations) without consulting their doctor. The injections should not be used if the fluid looks cloudy, has solid particles floating in it, or has separated. The injections should be stored away from sunlight and moisture. In addition, patients receiving multiple electrolyte injections should not stop them suddenly without telling their doctor, as the dosage may need to be reduced slowly before the TPN is discontinued.
- Sports drinks. Some persons do not like the salty taste of many sports drinks. They may wish to consider products containing glycine, which is an amino acid that neutralizes the salty taste of the electrolytes themselves. A more serious side effect of sports drinks, however, is tooth decay. An article published by researchers at the University of Maryland Dental School in 2005 showed that sports drinks erode tooth enamel at a rate three to 11 times faster than cola-based soft drinks.
- Over-the-counter powders and tablets. No side effects have been reported for these products.
- Over-the-counter electrolyte replenishers for children. Side effects may include allergic reactions, including hives, swelling of the face or hands, trouble breathing, tingling in the mouth or throat. Other side effects may include signs of too much sodium in the body, such as dizziness, seizures, muscle twitching, or restlessness. The doctor should be notified at once if any of these side effects occur. A less serious side effect that occurs in some children is mild vomiting.
- Oral rehydration formulae. May produce the same side effects as electrolyte replenishers for children.
- Multiple electrolyte injections. Minor side effects may include increased frequency of urination, dry mouth, increased thirst, or drowsiness. Serious side effects include rapid weight gain, yellowing of the skin or eyes, fruity odor on the breath, numbness or tingling in the hands or feet, uneven heartbeat, shortness of breath, confusion, or weakness with muscle twitching. Patients should notify their doctor at once if they notice any of these side effects.
- Sports drinks. Sports drinks may raise blood electrolyte levels in patients receiving total parenteral nutrition.
- Over-the-counter powders and tablets. No interactions have been reported.
- Over-the-counter electrolyte replenishers for children. Children receiving premixed forms of these preparations should not eat food with added salt or drink fruit juices until the diarrhea has stopped.
- Oral rehydration formulae for adults. No interactions with other medications have been reported; however, the doctor should be informed of all other medications that the patient is taking in case a dosage adjustment may be necessary.
- Multiple electrolyte injections. Sports drinks and other electrolyte supplements may raise total blood electrolyte levels in patients receiving these injections.
"Childhood Infections: Acute Infectious Gastroenteritis." Section 19, Chapter 265 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
"Fluid and Electrolyte Disorders in Infants and Children." Section 19, Chapter 259 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
"Nutritional Support." Section 1, Chapter 1 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
"Water, Electrolyte, Mineral, and Acid-Base Metabolism." Section 2, Chapter 12 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Almond, Christopher S. D., MD, MPH, Andrew Y. Shin, MD, Elizabeth B. Fortescue, MD, et al. "Hyponatremia among Runners in the Boston Marathon." New England Journal of Medicine 352 (April 14, 2005): 1550-1556.
Bovill, M. E., W. J. Tharion, and H. R. Lieberman. "Nutrition Knowledge and Supplement Use among Elite U. S. Army Soldiers." Military Medicine 168 (December 2003): 997-1000.
Comeau, Matthew J., PhD. "A Hot Issue for Summer Exercisers." ACSM Fit Society Page (Summer 2001): 4.
Froiland, K., W. Koszewski, J. Hingst, and L. Kopecky. "Nutritional Supplement Use among College Athletes and Their Sources of Information." International Journal of Sport Nutrition and Exercise Metabolism 14 (February 2004): 104-120.
"Position of Dietitians of Canada, the American Dietetic Association, and the American College of Sports Medicine: Nutrition and Athletic Performance." Canadian Journal of Dietetic Practice and Research 61 (Winter 2000): 176-192.
Rao, M. C. "Oral Rehydration Therapy: New Explanations for an Old Remedy." Annual Review of Physiology 66 (2004): 385-417.
Rice, Henry, MD. "Fluid Therapy for the Pediatric Surgical Patient." eMedicine, 17 September 2004. 〈http://www.emedicine.com/ped/topic2954〉.
Sawka, Michael N., and Scott J. Montain. "Fluid and Electrolyte Supplementation for Exercise Heat Stress." American Journal of Clinical Nutrition 72 (August 2000): 564S-572S.
von Duvillard, S. P., W. A. Braun, M. Markofski, et al. "Fluids and Hydration in Prolonged Endurance Performance." Nutrition 20 (July-August 2004): 651-656.
von Frauenhofer, J. A., and M. M. Rogers. "Effects of Sports Drinks and Other Beverages on Dental Enamel." General Dentistry 53 (January-February 2005): 28-31.
Wexler, Randell K., MD. "Evaluation and Treatment of Heat-Related Illnesses." American Family Physician 65 (June 1, 2002): 2307-2320.
American Society of Health-System Pharmacists (ASHP). 7272 Wisconsin Avenue, Bethesda, MD 20814. (301) 657-3000. 〈www.ashp.org〉.
Goodall, Roger M. "Oral Rehydration Therapy: How It Works.". 〈http://rehydrate.org/ors/ort_how_it_works.htm〉.
World Health Organization (WHO) Media Centre press release, 8 May 2002. "New Formula for Oral Rehydration Salts Will Save Millions of Lives." 〈http://www.who.int/mediacentre/news/releases/release35/en〉.