There's a debate, however, about whether the typical sports drink contains enough salt. The typical sports drinks contains less salt than sweat does, so it can't fully replace the salt lost through sweating.
Some experts believe that this discrepancy poses no threat to the athlete's performance or health. Others believe that it does, and advocate the use of salt supplements such as Lava Salts and/or extra-salty sports drinks such as Gatorade Endurance Formula during prolonged exercise.
Who's right? Do runners really need to fully replace salt losses during long workouts and races? A quick look at the relevant research answers this question easily. The evidence clearly demonstrates that a typical sports drink provides enough salt to optimize performance and protect the athlete's health, provided he or she doesn't overdrink. There's no measurable benefit associated with consuming extra salt. Let's look at some of the details.
Sodium is said to assist hydration in two ways. First, it's believed to increase the rate of fluid absorption from the gut into the bloodstream. And faster fluid absorption means faster hydration and less dehydration.
However, according to a pair of studies from the University of Iowa, sodium only increases the rate of fluid absorption if the fluid doesn't also contain carbohydrate. If the fluid does contain carbohydrate -- as most sports drinks do -- the amount of sodium contained in the drink (or consumed with the drink, in the case of salt tablets) has no effect on the absorption rate. The carbohydrate itself maximizes the rate of fluid absorption.
The second purported benefit of sodium with regard to hydration is that it helps athletes maintain a higher blood volume, which in turn keeps body temperature and heart rate from rising during prolonged exercise. Research has shown that sodium does indeed have these effects. However, a South African study found that a high-sodium sports drink was no more effective than a low-sodium sports drink in regulating body temperature and preventing "cardiac drift" (rising heart rate during prolonged exercise).
What can we conclude from these results? You don't need to consume as much sodium as you lose in sweat to keep your blood volume up and your temperature and heart rate down. The amount of sodium found in a typical sports drink will do the job. Taking in extra salt won't provide any additional benefit.
The major salt-related risk to the health of runners is hyponatremia, a potentially fatal condition that has received a lot of attention lately. Also known as water intoxication, hyponatremia results when the sodium concentration of the blood falls too low due to prolonged sweating combined with excessive fluid consumption. Symptoms include dizziness, muscle cramping, confusion, and stomach bloating. Severe cases can lead to seizure, coma and even death.
Because hyponatremia is characterized by low salt concentration in the blood, some experts advocate consuming extra salt during exercise as a way to prevent it. However, the primary cause of hyponatremia is not consuming too little salt, but is rather drinking too much fluid. Therefore the best way to avoid hyponatremia is not to consume more salt, but to drink less fluid instead.
A recent Swiss study compared the effects of three different fluids -- water, a low-sodium drink and a high-sodium drink -- consumed at a high rate of one liter per hour -- on the blood sodium levels and performance of runners in a four-hour run.
Despite the fact that the high-sodium drink contained almost as much salt as sweat, 46 percent of the study subjects developed mild hyponatremia when using it. While this percentage was slightly lower than the percentage of subjects who developed mild hyponatremia when using the low-sodium sports drink, these results clearly show that it's hard to avoid diluting your blood, now matter how much salt you consume, if you overdrink. (The current recommended drinking rate for runners is 400-800 ml/hr.) It's also worth noting that none of the three drinks tested in this study had any effect on performance as compared to the others.
Studies involving salt tablets -- which are popular among ultra-runners and long-distance triathletes -- have produced similar results. In a New Zealand study of Ironman participants, salt tablets were found to be unnecessary to maintain normal blood sodium levels.
The underlying conclusion we can draw from all of the research on salt intake in endurance events is that the typical sports drink provides plenty. Salt tablets and extra-salty sports drinks provide no additional benefits for performance or health protection.
This article was adapted by the author from The Cutting-Edge Runner: How to Use the Latest Science and Technology to Run Longer, Stronger, and Faster (Rodale, $15.95). Click here to purchase a copy.