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Nutrition – Electrolytes
By Alex McDonald, MD
Many athletes are familiar with the image of an athlete towards the end of their workout or race on a hot day, they are sweaty and often caked in a grainy white powder, electrolytes lost in sweat. Furthermore, many athletes have heard about the importance of sodium to consume to avoid the potentially lethal medical condition known as hyponatremia, low sodium levels in the body. Sodium is probably the most important electrolyte to consider on race day because of it’s role in maintaining hydration status in the body, however, potassium, magnesium, chloride and calcium should all be considered in a fueling/electrolyte replenishment plan. In this installment of 7 Principles of Ironman Fueling the importance of electrolytes and it’s impact on hydration will be explored.
Electrolytes Role in the Body:
In order for the nervous system to effectively communicate and coordinate various parts of the body, electrolytes, most importantly sodium, are required. Electrical activity, or action potentials, are generated within a neuron, or nerve cell, and pass along and between neurons, in an extremely complex pattern throughout the body to coordinate numerous functions. Without proper levels of electrolytes, the electrical signals in nerve cells cannot be established or transmitted and the nervous system will fail to function properly.
Muscle function requires electrolytes in a similar yet slightly different manner. Initially it is important to keep in mind that muscles require constant low level electrical stimulation from the nervous system to maintain form and proper function. Additionally, for a muscle to contract and create a voluntary or involuntary movement, electrical input from a nerve is required. If electrolyte levels are inadequate for neuronal function, then a muscle cell will fail to function properly as well. When an action potential from a nerve reaches a muscle, at the neuro-muscular junction, electrolytes enter the muscle cell causing a cascade of various other electrolytes and chemicals to be released which causes a muscle to contract. Without the appropriate levels of electrolytes this cascade could not occur and a muscle cell would be incapable of contracting or relaxing. This is in part why electrolyte levels are often blamed for muscle cramping during exercise. However, it should be noted that electrolyte levels are simply one component that can possibly be attributed to muscle cramping. The etiology of muscle cramps is not clear and certainly multifactorial.
The absolute concentration of electrolytes in the body is not as important as the relative ratios of different electrolytes compared in different parts of the body, specifically between the intracellular space (inside a cell) and in the extracellular space (outside a cell). The electrolyte levels in the blood and extracellular space is constantly in flux based on several different factors, mainly the amount of electrolytes, specifically sodium, consumed and lost on a daily basis.
There are numerous methods in which electrolytes can be gained and lost, and sodium levels are probably the most susceptible to, sometimes drastic changes. Electrolytes are obtained primarily through food and supplements and lost through sweat and urine. Blood electrolyte concentrations are maintained under precise control by various metabolic mechanisms, mainly: stimulation of thirst, secretion of antidiuretic hormone (ADH), aldosterone (another hormone) and handling of water, sodium and other electrolytes by the Kidney.
Although sodium is the primary electrolyte lost in sweat it is not the only one. As mentioned above calcium, magnesium, potassium and chloride are all components of sweat. Because of the delicate balance of electrolytes in the body it is important that an athlete not supplement with just sodium while racing and training. All five electrolytes are lost, so why would you just replace sodium? As has already been stressed numerous times, sodium is certainly the most important and an athlete can get away with just supplementing sodium, however, research suggests that replacing all five electrolytes with a sport drink such as EFS may improve performance.
The amount of each electrolyte that should be consumed during exercise is highly individual and should be based on the amount of fluid consumed, not on time. An athlete should determine their sweat rate (as described in installment number 5 of 7 Principles of Ironman Fueling – Training vs. Race Fueling) and therefore the amount of fluid they need per hour. The amount of sodium and other electrolytes that an athlete consumes should then be based on individual sweat rate and professional recommendations. For example, and because of it’s importance, The American College of Sports Medicine recommends that people who are active for more than one hour consume 500–700mg of sodium for every 32oz(~1 liter) of water they consume. However, there are some nutritionists who recommend 500-2000mg of sodium per 32oz of water per 1 hour of exercise. Experimental data has demonstrated that sweat rate and sodium loss is highly individual, ranging from 460-1840 mg/L of sweat. Sweat rate and electrolyte loss can vary drastically due to numerous variables including genetics, fitness, acclimatization, weather conditions and others factors. As such, both the sweat rate and the amount of sodium per oz/liter of sweat is highly individual and an athlete must experiment in training to find the right balance that works for their body and exercise conditions.
General guidelines for Ironman athletes: These are simply are starting point with which to practice in training. A quality sports drink, such as EFS, will have Sodium, Chloride, Calcium, Magnesium and Potassium is appropriate quantity and/or proportions, sodium is the one an athlete will have to experiment with the most. As you can see electrolyte needs vary greatly from one person to the next and practice is the only way to determine you personal needs.
Average amount of electrolytes lost in sweat:
Sodium – 900-2600mg/L
Chloride – 900-1900mg/L
Calcium – 50-100mg/L
Magnesium – 60-260mg/L
Potassium – 100-200mg/L
Sodium and Hydration:
First and very importantly, the Kidney plays a central role in water and electrolyte balance, and certain medications that many athletes consume regularly during a race, such as Non-Steroidal Anti-inflammatory Drugs (NSAIDs) (Advil or Motrin/ibuprofen, Aleve/naproxen or aspirin) can hamper the Kidney’s ability to appropriately handle sodium and free water. As a result these medications should be avoided before, during and after a race. If you want to take a pain reliever on race day, use Tylenol/acetaminophen as this medication is metabolized by the Liver and does not have a major effect on the Kidney.
Sodium levels and free water levels (plain water with no sodium or other electrolytes) are viewed and treated by the body as separate entities, however, are intrinsically linked. At any point the body can have too much free water, hypervolemia, or too little free water, hypovolemia, while at the same time having too much sodium, hypernatremia, or too little sodium, hyponatremia. The human body has very sophisticated systems to maintain very precise control on the level of free water and the level of sodium, and other electrolytes, in the body. When receptors in various parts of the body detect concentrations of sodium that are above or below the acceptable range various mechanisms are turned on or off to either retain or excrete sodium and/or free water.
For endurance athletes hypovolemic hyponatremia is of primary concern to their health while training and racing. That is when both the total body water levels (volemia) as well as total body sodium levels (natremia) are both low. This develops as sodium, other electrolytes and free water are lost, primarily via sweat and urine, and replaced by not enough and inappropriately hypotonic fluids (low sodium concentrations), such as plain water, or an electrolyte drink with too little sodium and other electrolytes as compared to the body’s electrolyte losses.
If the body detects hyponatremia, the Kidney will reabsorb sodium destined for the urine back into the blood stream. However, through osmosis some free water will follow back into the blood stream as well. The Kidney, will try to correct for low sodium and other electrolyte concentrations, however, to completely correct the imbalance sodium must be consumed.
The concept of osmosis (water flow across a semi-permeable membrane until the concentration is equal on both sides) is also the cause behind the major health risks of hyponatremia. When blood sodium concentrations fall rapidly (as they would in an endurance event) there is a higher sodium concentration inside the cells of the body than outside. This causes water to flow from the blood stream into the cells and the cells swell. Have your hands ever become puffy during an endurance race? Most tissues of the body can easily tolerate this swelling; however, the brain is not. The brain is confined by the skull and when brain cell swell pressure begins to build, a condition known as cerebral edema develops, and if the edema is severe enough, can cause death.
Life threatening hyponatremia is relatively uncommon and symptoms can include decreased appetite, nausea and vomiting, difficulty concentrating, confusion, lethargy, agitation, headache and seizures. At the first sign of nausea, muscle cramps or disorientation, an athlete should drink an electrolyte, most importantly sodium, containing sports drink, such as EFS, or eat salty foods. If the symptoms are extreme, a medical professional should be sought.
Electrolytes play a key role in numerous metabolic processes in the body as well as having a major impact on hydration status. Additionally, proper electrolyte supplementation, specifically sodium, is critical to avoid the potentially life threatening condition of hyponatremia. Lastly, all five electrolytes are lost in sweat and as such all five should be replaced in a nutrition plan for optimal athletic performance.