Sodium: A Closer Look

Alex M. McDonald, MD
Sodium is an important part of every athlete’s diet. Athletes have higher sodium needs compared to the general population because sodium loss escalates when one sweats. Sodium is also required for optimal hydration before, during, and after exercise. The specific amount is highly individual and must be practiced in order to determine your appropriate nutrition strategy.

Through proper practice and training, athletes can maintain balanced hydration and avoid many of the pitfalls of improper sodium intake, particularly the life-threatening condition of hyponatremia. In this article you will gain a better understanding of sodium as a critical electrolyte required for proper body function.

Sodium’s Role in the Body

Sodium is one of the many electrolytes required for human life. The body makes use of sodium in many ways: It plays a key role in muscle and nerve function, and it’s the electrolyte responsible for maintaining fluid levels in various parts of the body.

Although appropriate functioning of nerves and muscles requires sodium, it is not the absolute concentration of sodium that is critical – it’s the ratio of sodium inside a cell compared to sodium outside a cell that is important.

Of the many methods in which sodium can be gained and lost, the intake of food and the output of sweat and urine are the most important.

Sodium and Exercise

Sodium is the primary electrolyte lost in sweat. Therefore, when exercise exceeds one hour, the American College of Sports Medicine (ACSM) recommends consuming sodium along with fluids to replace both water and sodium lost in sweat. It is not adequate to simply take sodium tabs after a hard training session to replace lost sodium; an athlete must also consume adequate amounts of fluid with this sodium.

Some athletes believe using sodium supplements helps them avoid muscle cramps. Although appropriate sodium levels are required for proper muscle function, there is no definitive cause for cramps. Muscle cramps are commonly attributed to hypovolemia (low total body water) and/or hyponatremia (low sodium levels). Seeking an optimal nutrition plan, including hydration and sodium supplementation, can help address the muscle cramp that some athletes believe is associated with sodium lost from sweat.

Because sodium and water are required in appropriate ratios based on an athlete’s sweat rate, it is recommended that an athlete determine their sweat rate based on various conditions. Studies have shown that sweat rate and sodium loss is highly individual. The American College of Sports Medicine recommends that people who are active for more than one hour consume 500‐700 mg of sodium for every 32 oz of water they consume.

Athletes must experiment in training to find the right balance that warrants for their body and exercise conditions. Determining sweat rate can be an inexpensive and convenient way to estimate sweat‐related sodium loss. If you know how much weight you lose via sweat during a workout, then you can estimate the amount of sodium you need. This entails some trial and error, but it can work just as well as more expensive tests.

Hyponatremia: A Closer Look

For endurance athletes, hypovolemic hyponatremia is a major health concern while training and racing. Hypovolemic hyponatremia happens when both the total body water levels (volemia) as well as total body sodium levels (natremia) are low. This condition develops as sodium and free water are lost, primarily via sweat and urine, and replaced by inappropriately hypotonic (low sodium) fluids, such as plain water or an electrolyte drink with too little sodium to cover the body’s sodium losses.

When a body’s concentration of sodium is low, the kidneys will reabsorb sodium destined for the urine back into the bloodstream. When this occurs, a concentration gradient is established, and water that was destined for the urine will “follow” sodium back into the bloodstream, as well. As a result, when there are low sodium concentrations in the blood, the body (specifically the kidneys) will try to correct the imbalance; however, it requires sodium from an outside source to fully correct the imbalance.

In the early stages of hyponatremia, you may feel dehydrated and only drink water; however, this will only worsen the problem. At the first sign of nausea, muscle cramps or disorientation, you should drink a sports drink containing sodium or eat salty foods. If the symptoms are extreme, seek medical help immediately.
If you feel you are experiencing hyponatremia, be aware of these symptoms:
  • Decreased appetite
  • Nausea and vomiting
  • Difficulty concentrating
  • Confusion
  • Lethargy
  • Agitation
  • Headache
  • Seizures

When Your Doctor Advises You to Avoid Sodium

Sodium chloride (salt) is ubiquitous in the Western diet, and has gotten a bad reputation. While individuals with high blood pressure, kidney or cardiac problems, and other medical conditions need to avoid sodium, but if you’re an endurance athlete you may require a higher level of sodium during training and competition and should discuss with your doctor.

There are significant amounts of sodium in many foods, particularly those that are prepackaged or served in a restaurant. For example, a single serving of many frozen dinners can contain almost 1,000 mg of sodium, almost half of one’s recommended daily intake. Individuals that are physically inactive and consume large amounts of sodium could be putting themselves at risk for health problems later in life.

Because athletes lose more sodium than the average population, they may have slightly higher daily sodium needs than the average population. In addition to sodium intake during exercise, consuming adequate sodium before and after exercise is important for optimal hydration.

Sodium is an essential electrolyte, and should not be avoided: Individuals should simply be aware of how much sodium is in the foods they consume.


References:

1. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2004), National Academy of Sciences. Institute of Medicine. Food and Nutrition Board.
2. Maughan, R.J. 1986. Exercise‐induced muscle cramp: A prospective biochemical study in marathon runners. Journal of Sports Sciences 4 (1): 31‐34.
3. Schwellnus, M.P., et al. 1997. Aetiology of skeletal muscle "cramps" during exercise: A novel hypothesis. Journal of Sports Sciences 15 (3): 277‐285.
4. Casa, DJ., Clarkson, PM., Roberts, WO., American College of Sports Medicine Roundtable on Hydration and Physical Activity: Consensus Statements. Current Sports Medicine Reports 2005, 4:115–127.
About The Author

A graduate with a medical degree from the University of Vermont and also the Amateur Ironman World Champion at Kona 2007, Alex is temporarily putting his medical career on hold to race as a professional triathlete.

Fun Fact: While a 4th-year medical student, Alex found time to train and win Ironman USA Lake Placid in 2007

Information presented by PowerBar is intended to impart general sports nutrition and training information. PowerBar is not engaged in rendering medical advice or services. Be sure to consult your doctor as needed, including when undertaking a new diet or training program. Advance consultation with your doctor is particularly important if you are under eighteen (18), pregnant, breastfeeding, or have health problems. Never disregard professional medical advice or delay in seeking it because of something you have read on PowerBar’s site.