Water Toxicity: A Growing Concern

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For most Americans, the idea that drinking too much water is unhealthy seems far-fetched. However, if one takes a course in toxicology, one of the first things you will learn is the dose makes the poison. Simply put, nothing is toxic if the dose is low enough, and everything is toxic if the dose is high enough. This is true even for a substance as critical to life and health as water.
Last year the danger of drinking too much water over a short period of time was made clear by the death of an apparently healthy 28 year old mother of 3 who died from acute water intoxication as the result of radio show contest called “Hold your wee for a Wii”. The KDND-FM radio “Morning Rave” show had 18 contestants compete for a Wii by drinking as much water as they could without urinating. According to Sacramento County Coroner's Office the woman was apparently in good health and died as result of “water intoxication.”
It is not clear how much the woman drank but another contestant said he quit after eight 8 oz glasses of water and this woman kept going.
When plain water or other beverages including sport drinks are consumed in large amounts over several hours this can lead to the dilution of electrolytes like sodium and chloride in the blood. Low sodium (<135mmol/L) in the blood or hyponatremia frequently results when fluid intake dilutes the blood too much. If serum sodium drops below 120mmol/L it can lead to death. Dilutional hyponatremia results in brain swelling and is usually accompanied by headache, nausea, lethargy, vomiting, disorientation and convulsions.
For many years, endurance athletes have been encouraged to drink before and during endurance events. The American College of Sports Medicine (ASCM) for years recommended endurance athletes consume 600 to 1200ml of fluid per hour. However, such guidelines to drink well in excess of thirst appear to be largely responsible for a growing epidemic of hyponatremia in endurance athletes. A study of 488 runners in the 2002 Boston Marathon found that 13% finished the race with hyponatremia and 3 had a critically low serum sodium level (<120mmol/L). Researchers noted that smaller people who took longer to finish the race were at higher risk of hyponatremia especially if they gained weight during the event. They also found that drinking sports drinks with added salt was not associated with any reduction in the risk of hyponatremia.1
Certainly drinking too little water and becoming dehydrated can lead to heat stroke, which is also dangerous. While many sports nutrition experts tell people that they should drink enough to prevent weight loss during an endurance event this may not be the best advice. Certainly the loss of about 0.5% of one’s initial weight during the first 3-4 hours of competition will or not impair athletic performance or lead to heat stroke. In ultra-endurance events lasting more than 4 hours but less than 16 hours, one should probably try to limit weight loss to no more than about 3 to 4% of one’s initial body weight.
Because of growing concerns about hyponatremia there is a growing trend of adding more salt to sports drinks and encouraging people to consume more salty foods before a race. Unfortunately eating more salt lowers aldosterone levels in the blood and greatly increases the amount of salt lost in the sweat. The resulting increased loss of sodium in sweat may very well increase the risk of severe hyponatremia. In any case, Americans already suffer from salt toxicity and one cannot justify the use of more salt as a solution to a problem that is fundamentally caused by consuming too much fluid. Indeed, a usual diet low in salt results in far less salt lost in sweat and may actually reduce the risk of hyponatremia.
Bottom Line:
Drinking fluid well in excess of thirst can result in hyponatremia, which can impair athletic performance and in extreme cases can even be life threatening. Encouraging athletes to consume more salt and saltier sports drinks are of no proven value to preventing hyponatremia but certainly increase the risk of hypertension in the long run.
By James J. Kenney, PhD, RD, FACN.
References:
1 N Engl J Med 2005;352:1550-6

Drinking Tips for Athletes
1. Drinking large amounts of fluids in a short amount of time can cause hyponatremia and lead to fatal brain swelling.
2. Drink water or other fluids in sufficient quantity to quench thirst. This includes loading up on fluid before or during an event.
3. Gaining weight during an endurance event is a sure sign you are over-hydrating.
4. It’s okay to lose about 0.5% of your body weight, or about 1/2 pound per 100 pounds of body weight, per hour for events that last up to 4 hours. This is not dehydration and will not impair athletic performance.
5. Losing up to about 4%  of body weight for events lasting 4-16 hours, or about 4 pounds per 100 pounds of body weight is expected given glycogen depletion and some body fat.
6. Increasing the salt content of sports drinks can put you at a risk for hypertension in the long term. Higher salt intake of beverages is not the solution to overhydration and hyponatremia caused by excess fluid intake. J.K.

Sports Drink Calories
Did you know that a 20 ounce bottle of Gatorade contains 35 grams of sugar or about 8.75 teaspoons? Of course, this is a better choice than a 20 ounce bottle of cola which contains 65 grams of sugar or about 16.25 teaspoons! The bottle of Gatorade will set you back about 130 calories or the amount of calories burned in the gym in  40 minutes. Gatorade is good for endurance athletes who work out for more than an hour.  But not necessary for most recreational athletes who are likely to eat too much sugar already. Your best bet? Water as your thirst requires it and fresh fruit for a snack afterwards instead of bags of chips!

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