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Balancing the new info
on water, salt

How much water is too much, and how much is too little? Last week, an article in the New England Journal of Medicine reported that 13 percent of runners in the 2002 Boston Marathon drank too much water or sports drinks and developed hyponatremia. A female participant died after the marathon due to hyponatremia. Many news reports on this study emphasized that drinking too much water can be dangerous. This might have confused people for whom it is not really an issue.

Question: What is hyponatremia?

Answer: This is the medical term for low levels of sodium in the blood. Normally, the body carefully regulates the concentration of sodium in its fluids, keeping blood-sodium levels within a narrow range. When sodium levels drop too low, nausea, lightheadedness, bloating, cramping, impaired brain function and even death could result.

Q: Who is susceptible to hyponatremia?

A: Some extreme conditions can cause sodium to drop too low. The most common cause is loss of sodium due to heavy sweating in combination with drinking large amounts of fluids that contain little or no sodium. Generally, this occurs only during long bouts of exercise, such as a marathon, lasting four hours or longer.

In four hours of exercise, it is typical for athletes to lose six quarts of water (12 pounds) in sweat. If they don't replace some of this water loss, their body can overheat, and they will become a medical emergency due to dehydration.

The endurance athlete also can lose more than 15 grams (three teaspoons) of salt in four hours of sweating. Drinking too much water (without replacing the lost salt) can overly dilute body fluids and cause hyponatremia.

Q: Should an athlete drink enough fluids to prevent losing any weight during exercise?

A: Athletes probably should not lose more than 2 to 3 percent of their body weight during exercise -- which is about three to four pounds in a 150-pound person. In a four-hour marathon, a runner burns about a pound of carbohydrates stored in the body in a form called glycogen. Because glycogen holds onto water like a sponge in the body, the loss of one pound of glycogen releases about three pounds of water. This water cannot be replaced until substantial amounts of carbohydrates are consumed to replace the glycogen. Attempting to replace all of this water during exercise can overly dilute body fluids and result in hyponatremia, especially if more water is consumed than lost.

Q: Who needs to decrease their water intake in Hawaii?

A: Because few of us run marathons often, drinking too much and the risk of hyponatremia are not issues. Drinking too little is much more common.

When the body seems to poorly hold onto water, the problem could be an extreme diet that does not provide adequate amounts of protein, carbohydrates or salt. All three help maintain water in the cells and in the blood. Most of us get more than enough.

Both water and sodium are essential nutrients, which means that we require them in the diet. As with any nutrient, it all comes down to a balance -- not too much and not too little.

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