For decades, we have been taught the importance of lowering our intake of dietary salt and of making sure that we drink plenty of water, particularly when exercising. However, in rare cases, a person can actually take in too much water and not enough salt, resulting in a condition called hyponatremia (a Latin term meaning too little salt). Also called water intoxication, this condition occurs when the level of salt in the blood becomes too low, generally from excessive sweating or from serious health conditions such as kidney disease, heart failure, cirrhosis of the liver, or Addison’s disease. This upsets the body’s natural balances and causes it to retain too much water.

Salt is an important nutrient that contributes to the healthy functioning of nerves and muscles, including the heart. When too much salt is lost, it can cause symptoms such as confusion, dizziness, weakness, lethargy, irritability, cramping, nausea, bloating, headache, twitching, fainting, and hallucinations. In extreme cases, hyponatremia can lead to seizures, coma, and even death.

Hyponatremia is a particular concern for long-distance runners or other ultraendurance athletes. It can be prevented if athletes make sure to replenish their salt as well as their water supply. Good sources include salty snacks, such as pretzels and tomato juice, or special sports drinks, such as Gatorade, that include needed electrolytes and salt.

For more information:

• The New England Journal of Medicine article "Hyponatremia among Runners in the Boston Marathon"
  • http://content.nejm.org/cgi/content/short/352/15/1550
• National Institute of Health definition and description:
  • http://www.nlm.nih.gov/medlineplus/ency/article/000394.htm
• Rice University article "Salt and the Ultraendurance Athlete"
  • http://www.rice.edu/~jenky/sports/salt.html
• Rice University article "Hypynatremia and Exercise, Part 2 - Mechanisms"
  • http://www.rice.edu/~jenky/sports/hyponatremia.html