How Much to Drink During a Marathon

Two newly released studies show that a worrying large percentage of distance runners may not know how to drink.

Some runners may be drinking too much water or other fluids. Others may be taking in too little. And a disconcerting majority don’t seem to be concerned about whether they are drinking a safe amount at all, according to the new reports.

Attitudes and expert guidelines about how much fluid people should drink during prolonged endurance events have changed drastically in the past 15 years. A 1996 Position Stand from the American College of Sports Medicine concluded that “athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated.” Many of us who ran a marathon in the 1990s were cautioned to “stay ahead” of our thirst, with the warning that by the time we felt thirsty, we would be clinically dehydrated. (Formal definitions of dehydration vary, but most experts agree that losing more than 3 percent of your body weight can be considered dehydration.)

But in the past few years, several marathoners died as a result of drinking too much, a dangerous condition called hyponatremia, or water intoxication. Before then, hyponatremia, marked by low blood sodium levels, had been unheard of in marathon fields. Twenty years ago, a typical marathon racer strode fast and drank little. But as the event gained popularity, finishing times rose. Slower runners generally sweat less, and many have been told to drink copiously. If you ingest more fluid than you lose through sweating or urination, however, you dilute your blood’s sodium levels. Osmosis then draws water from the blood into body cells to equalize sodium levels, and those cells swell. If the cellular bloating occurs in the brain, it can be fatal.

Most experts have now begun advising marathon runners to drink less. They’ve focused on marathoners because hyponatremia is uncommon in events that last less than four hours or so (at least for middle-of-the-pack and slower competitors). Recent guidelines from the International Marathon Medical Directors Association explicitly say to drink only when you’re thirsty.  Read More

Dr. Jay’s Note:  Looks as if, just like carbs, loading up on fluids for a few days prior to an endurance event does not carry with it all of the benefits that we once thought. Listen to your body & stick to drinking pure water when thirsty. Sports drinks, artificially flavored & sweetened beverages, energy drinks & enhanced/smarter waters should always be avoided.

Also, if your urine is not consistently clear, you need to drink more purified water.