April 2021 Issue
Electrolytes’ Role in Optimal Hydration
By KC Wright, MS, RDN
Vol. 23, No. 4, P. 28
An Overview of the Current Guidelines, Athletes’ Needs, and Practice Pearls for RDs
For athletes of any skill level, adequate hydration is imperative for optimal health and exercise performance. Yet, research suggests that more than one-half of athletes in professional, collegiate, and high school and youth sports aren’t sufficiently hydrated before exercise even begins.1
The human body loses water daily through respiration, gastrointestinal functions, renal processes, and perspiration, which all can be replaced from a typical day’s food and beverage consumption. Athletes, however, experience additional fluid loss through increased perspiration in the form of sweat, which functions to maintain body temperature. In fact, the body readily can produce a quart of sweat daily.2 Consequently, good fluid management before, during, and after exercise is important for athletes to prevent dehydration.
Sweat is composed mainly of water, approximately 99%, and just 1% electrolytes, yet the role electrolytes play in fluid balance is critical. Both water and a variety of foods in a typical daily diet can replenish electrolytes in the body. While there’s a myriad of electrolyte replacement products on the market, addressing consumer concerns about these options can be challenging. This article addresses the role of electrolytes in sports, current professional guidelines, strategies to assess clients’ needs, and recommendations for dietitians.
Recall from junior high science class that the body is composed of 50% to 70% water, so it makes sense that fluids lost must be replaced daily. Total body water is compartmentalized within the spaces among cells—approximately 65% intracellular and 35% extracellular. Water in the body follows the movement of electrolytes, which demonstrates their importance—the balance of cellular water is vital.3 If a fluid compartment has a high concentration of electrolytes, fluid moves into that compartment through osmosis. Similarly, if the electrolyte concentration is low, fluid will move out of that compartment. All water compartments can dehydrate with sweating, but to adjust fluid levels, the body can actively move electrolytes in or out of cells. In humans, total body water and overall hydration normally are maintained within a relatively narrow range—1% hyperhydration (excessive total body water content) to 3% hypohydration (uncompensated loss of body water.)1
Electrolytes are minerals that dissociate into positively or negatively charged ions (cations and anions, respectively) when dissolved in water. Sodium is the major cation, while chloride is the principal anion of extracellular fluid. Potassium is the major cation of intracellular fluid. Beyond fluid balance, electrolytes also conduct electrical activity and are involved in muscle contraction and neural activity. One of the functions of the kidneys is to maintain an adequate balance of electrolytes by filtering them and water from blood, returning some to the blood, and excreting any excess in urine.
For athletes, maintaining fluid balance is important for many reasons, including sustaining heart stroke volume and sweat rates, enabling delivery of nutrients to working cells, and enhancing removal of metabolic waste products from cells.4 Exercise can disturb fluid balance through sweat loss, which in turn can affect an athlete’s performance and safety. When athletes lose water through sweat, the sweat contains electrolytes, mostly sodium and chloride and a smaller amount of potassium.5 Sodium and potassium regulate the amount of body water, while chloride maintains osmotic pressure. Low concentrations of other electrolytes, specifically magnesium and calcium, also are lost with sweat. The losses of electrolytes vary significantly between athletes and are dependent on total sweat losses and the concentration of electrolytes in the sweat. Dehydration alone can increase the concentration of both sodium and chloride lost in sweat.6
Although thirst is regulated by the central nervous system and may be a useful indicator during daily life, it’s relatively benign when tracking hydration during exercise.7 Thirst results once an athlete develops dehydration at a loss of approximately 1% to 2% of body mass.8 Maintaining optimal hydration during athletic performance can be complicated depending on the sport, type of activity, and availability of fluid. Environmental temperature appears to be the main factor that influences athletic performance in response to hydration.7 As athletes become more acclimatized to a warmer environment, they adapt by enhancing their capacity to reabsorb both sodium and chloride.6
Professional Recommendations for Fluid/Electrolyte Replacement
Based on extensive literature reviews and the use of evidence-based analyses, current consensus recommends that good hydration practices include euhydration before exercise, preventing hypohydration during exercise, and replacing remaining fluid losses following exercise and before the next exercise period. Fluid needs are dependent on the individual, influenced by personal sweat rate (a function of metabolic heat production), exercise mode, intensity, environmental conditions, and duration. Exercise intensity mainly determines metabolic heat production.
The current joint position of the American College of Sports Medicine, the Academy of Nutrition and Dietetics, and Dietitians of Canada states that dehydration occurs with a fluid loss >2% body weight, and that this can impede cognition and exercise performance, especially in hot weather.9 Most research suggests that if weight loss from fluid and dehydration are maintained at <2% during exercise, they don’t affect performance of well-hydrated athletes who replenish fluid loss afterwards.5 Euhydration, the state of optimal total body water content, before exercise can be attained by drinking 5 to 10 mL/kg body weight in fluids within two to four hours before activity, resulting in urine the color of pale yellow. The National Strength and Conditioning Association offers similar hydration guidelines (5 to 7 mL/kg at least four hours before exercise).10
The rate of sweat loss during exercise may vary with intensity, duration, fitness, heat adaptation, and other environmental conditions. It’s estimated that 1 kg of body weight loss suggests 1 L of sweat loss, which may be compensated by an average intake of 0.4 to 0.8 L of fluid per hour of exercise.9 The American College of Sports Medicine joint position guidelines suggest that athletes who sweat excessively (>1.2 L/hour), or have “salty sweat,” or participate in exercise lasting more than two hours should ingest some sodium. A “salty sweater” will have a salt residue on skin and/or clothes during and/or after exercise. Sodium consumed with preexercise fluids and foods may help with fluid retention.6
The National Athletic Trainers’ Association (NATA) position statement on fluid balance recommendations during physical activity specifies that hydration status should have minimal variation (+1% to -1%) to allow the body to optimally thermoregulate and preserve healthy cardiovascular function.1 According to the NATA, water or other palatable fluids should be easily accessible before, during, and after exercise, and individuals should refuel with food and drink within two hours of physical activity to replace fluid, electrolytes, carbohydrate, and protein. The NATA position statement also suggests that most individuals can avoid fluid balance problems by drinking when thirsty during and after exercise and eating a healthful diet.
The characteristics of a certain sport often dictates the opportunity for athletes to hydrate themselves during performance; thus their hydration strategy for competition is based on their particular sport, according to a research review of hydration and sports-associated hypohydration risk based on sweat losses, availability of fluid, environmental conditions, and intensity of exercise for both team and individual sports.7 Basketball, baseball, softball, and volleyball have a relatively low risk of hypohydration during training and competition, while ice hockey, football, and lacrosse were found to have a moderate risk during each performance. For soccer and rugby, training presented a moderate risk of hypohydration whereas competition elevated the risk to high, as the timing of play often limits opportunities to drink.
With individual sports, gymnastics, running or cycling for less than an hour, and swimming all presented a low risk of hypohydration in training and competition; tennis and more than one or two hours of running presented a moderate hypohydration risk. Training for wrestling presented a high risk due to restricting fluid to make weight class, while competition is deemed a low risk. More than two hours of cycling training hours is considered a low risk of hypohydration, but competition cycling presents a high risk.
Cycling and running rely on consistent movement in a steady state. Here, increased fluid intake is necessary due to greater sweat production with exercise intensity and duration. Team sports such as football and basketball involve shorter exercise bouts with breaks in between, where an average of exercise intensity should be used to determine optimal fluid balance.5 Since all clothing provides some insulation and a barrier to heat loss resulting in increased sweat rates, it should be noted that an athlete wearing a football uniform, complete with helmet, may have greater fluid loss when compared with a track runner with minimal clothing.
Exercising in cold weather can produce significant sweat while diminishing thirst sensitivity, as the cold inhibits arginine vasopressin, a fluid-regulating hormone that stimulates thirst.11 In addition, sweat evaporates rapidly in cold, dry air, while most of the fluid loss is through respiration. Both of these factors can trick the body into thinking it doesn’t need to replenish fluid. Training or competing in higher altitudes also may require additional fluids, as the elevation tends to increase water and electrolyte losses and decrease both plasma volume and total body water content.7 Humidity is an additional factor to consider, as it can create a significant fluid deficit rapidly.
Assessing Hydration for Best Athletic Performance
It’s important to assess hydration before activity, and, if possible, during performance and competition, but especially afterward. Experienced sports RDs who are board-certified specialists in sports dietetics can provide assessments of nutritional needs, interpret test results, and develop a dietary prescription to help athletes maintain adequate hydration for optimal performance. (For more information, visit scandpg.org.)
Dietitians can estimate hydration in two ways, first by assessing changes in weight from the morning (after voiding) and post exercise, and second by measuring the concentration of solutes in the urine through specific gravity and urine osmolality analysis. In a laboratory or clinic setting, body mass assessment can measure hydration status, and a weight scale also can be used to assess fluid deficits before and after practice. When comparing pre- and postexercise weight, consider significant amounts of fluid trapped in hair and clothes.
Specific Hydration Strategies
While assessing hydration is paramount, dietitians also need to educate athletes on electrolytes and the important role they play in rest and exercise. Consider the type of exercise, whether it’s prolonged, intense, or both; increase availability of fluids during training and performance; and consult with training staff and coaches to schedule breaks during prolonged practices or with more intense exercise. In addition, keep environmental conditions in mind and modify practice schedules if possible.
When opportunities to drink during practice or competition are limited, encourage athletes to use breaks or timeouts to rehydrate. Keep individual characteristics in mind, such as whether the athlete has a high sweat rate. Perhaps RDs can work with an exercise physiologist to test sweat rates of those who have issues. Body size is an important consideration for an individual’s sweat rate. For example, larger athletes typically have higher sweat losses, with football linemen exhibiting some of the highest sweat rates recorded.7
Monitor athletes who participate in appearance-based sports such as gymnastics, ice skating, and lightweight rowing, to assess whether they’re intentionally restricting fluid to enhance their appearance or meet lighter competition weight classifications. Counsel athletes who may be sacrificing performance and endangering their health with purposeful fluid loss to enhance body image, and promote healthy weight management as a part of performance goals.
Practical Hydration Solutions
It’s important to consider that every athlete is an individual and that nutrition plans need to be personalized, with dynamic nutrition goals and recommendations, especially given the stages of training, competition, and recovery. Under normal circumstances, physically active people consuming a well-balanced diet shouldn’t need to add specific ingredients to their fluids before, during, or after exercise. In athletic events lasting up to 45 minutes, the risk of dehydration is low as there’s limited time for sweat loss to accumulate.5 Unless an athlete is a salty sweater, there’s no need for electrolyte intake before exercise.6
But if heavy sweating is expected during exercise—perhaps due to extended duration greater than 60 to 90 minutes, increased intensity, or high ambient temperature and humidity—a salty snack such as a pickle or a sports drink instead of water may be warranted for preexercise hydration. The sodium in the drink will help the body absorb and retain the fluid and use the carbohydrate. For the body to retain fluid, the drink must be consumed with foods that contain sodium and other minerals.6 Food and beverages containing plenty of sodium such as salty nuts and snacks and tomato juice can help recover fluid loss, but if these aren’t readily available, a sports beverage or other product can be used to replace electrolytes.
Electrolyte Product Market
In 2017, the global market for electrolyte hydration products was valued at $1.42 billion, and it’s expected to reach $1.82 billion by 2025, gaining increased popularity among millennials and members of generation Z who engage in vigorous exercise.12 As part of a big industry, many of these products are promoted with intense marketing efforts, even when they’re not needed. Some bottled water infused with electrolytes is available in convenience stores and may appeal to young people looking for a competitive edge and/or more energy. But consumers who exercise moderately for less than an hour are better off drinking plain water; these beverages are sold at high prices and may contain additional sugar, calories, and caffeine. If warranted, RDs can help athletes weigh the pros and cons of using electrolyte replacement products. Some brands of electrolyte-enhanced bottled water don’t contain any more electrolytes than are found in standard household tap water, which contains just 2% to 3% of daily needs.13 Thus, it’s important to educate consumers on what the products contain and encourage them to read labels.
Conversely, commercially available electrolyte replacement products are formulated to meet the needs of most athletes, but no single formulation can meet individual variability. Products targeted at replacing electrolytes lost through exercise include food, sports drinks, sports gels, and sports candy or gummies and contain varying amounts of carbohydrates. Products can be ready-to-drink or powder mixes, tablets, and capsules that dissolve in water. An 8-oz serving of an electrolyte drink typically has around 14 g sugar, 100 mg sodium, and 30 mg potassium. Specialty formulations with higher levels of sodium and potassium and the addition of other minerals such as calcium and magnesium are available for endurance and ultraendurance athletes.
While electrolyte replacement products can be beneficial, RDs should make athletes aware that alcohol and excess consumption of caffeinated beverages such as coffee and tea also can contribute to dehydration.1 Overall, it can be challenging for athletes to navigate their electrolyte replacement needs and the growing arena of commercial products on the market. Consulting with or a referral to a board-certified specialist in sports dietetics can help ensure athletes are guided for good health and performance.
— KC Wright, MS, RDN, is a research dietitian providing clear messaging about nutrition science and real food for the health of people and the planet. She advocates for sustainable food and food systems at wildberrycommunications.com.
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