Every person in the Western world consumes more than sufficient quantities of salt through their diet to satisfy their bodily needs for sodium, one of the two elements that form salt; 90% of all dietary salt consumed is excreted through the urine as excess. In the pre-industrialized world, the reliance on whole, non-processed foods created a natural balance in the body between sodium and potassium, present in most fruits and vegetables. Salt is one of the most important substances consumed by athletes, as salt is crucial to the proper function of a number of bodily systems, all of which are essential to athletic performance. Salt is composed of the elements sodium and chlorine, with sodium comprising 40% of the total weight of salt. Sodium is chemically classified as a metal of the type known as an electrolyte, capable of carrying and transmitting an electrical charge.
Sodium is essential in many bodily processes, including the maintenance of optimal fluid levels within the body; sodium levels are the key determination of how much water will be retained within the body and how much water will be excreted as urine. Sodium is a substance that is very soluble in water and virtually all sodium ingested into the body will be absorbed through the small intestine. The hormone aldosterone, which is produced in the adrenal gland, is the chemical that regulates sodium levels.
Sodium also maintains the acid/base level within the body, usually expressed as the pH balance. Additionally, it helps in the relaying of nerve impulses into the skeletal muscles, through a mechanism known as the sodium/potassium pump, where sodium and potassium act in concert to maintain the electrochemical balance within the muscle cells that permits the impulse to reach the muscle fiber.
Sodium is depleted in exercise through a number of mechanisms within the body. Approximately 85% of the sodium in the body is contained within the bloodstream. Sodium levels are constantly influenced by the generation of perspiration and urination. A healthy person requires a maximum of 3,000 mg of sodium per day to maintain proper sodium/fluid balance. The body does not possess an organic facility in which sodium can be stored and accessed at a later time. In vigorous exercise, or in warm weather conditions, an athlete may lose more than 1,000 mg of sodium per day. The primary cause of sodium loss is through perspiration and resultant fluid loss. When sodium and fluids are depleted together, a chain reaction is triggered. The sodium in the bloodstream that is necessary to maintain the body's balance will be depleted as fluids are lost, which creates a reduced blood volume. Lower blood volumes will result in lowered blood pressure in the cardiovascular system, which generally will reduce the ability of the system to function at an optimal level. A common physiological result of this sodium loss progression is muscle cramps, particularly in the lower leg and calf muscles.
When an athlete replenishes the fluids lost through perspiration with water only, producing an unequal replacement of water versus sodium, the desired sodium balance, or osmolarity, present when the body is in homeostasis (balance) is correspondingly reduced. This condition is known as hyponatremia, or water intoxication. This conditions renders the athlete extremely fatigued, uncoordinated, and at risk of significant further dehydration, as the water ingested into the body will flood the cells, and it will not be absorbed into the bloodstream to boost blood volume, as the body will involuntarily seek to maintain as high a sodium level in the body's fluids as possible. This condition also causes poor carbohydrate metabolism, which reduces the ability of the body to generate musculoskeletal energy.
The opposite state experienced by athletes who consume too much sodium relative to their fluid levels is hypernatremia, created when the body senses that the ratio of sodium to fluid is too high. The body releases the anti-diuretic hormone, ADH (vasopressin), to chemically trigger a shutdown in the production of urine, in an effort to keep the level of fluid higher in relation to the increased sodium level.
The body excretes excess sodium through the urine processed by the kidneys. Excess sodium to the extent of causing toxicity in the body is rare among athletes. The greater risk of excess sodium is the creation of either transient high blood pressure or hypertension, an indefinite condition that places undue stress on the function of the entire cardiovascular system.
The sodium levels necessary for an athlete to perform are maintained entirely through diet; it is during and immediately after competition that additional sodium is beneficial. Almost all conventional sport drinks do not possess sufficient amounts of sodium to assist in the replacement required by an athlete in warm or physically taxing conditions; to achieve total sodium replacement the drink would have to have the composition and the taste of sea-water. As an athlete should ideally consume sufficient fluids to replace all perspiration lost, the amount of sodium contained in that lost fluid must be replaced as well. Salt tablets are often used to bolster sodium levels because they contain a far greater concentration of sodium than does any sports drink. Athletes who compete in ultra-marathons or Ironman competitions, events that take place over many hours, sometimes employ low-tech strategies in the consumption of additional sodium. Eating salty pretzels is a favorite among some members of the ultra-marathon community to increase sodium consumption during an event or lengthy training session.