Drink Wisely During Exercise
Too Much Fluid Can Be As Bad As Too Little
July 17, 2003 -- Forget that advice to drink all you can before, during, and
For water and for sports drinks, the new message is to drink wisely. Too
many fluids are at least as dangerous as too few. But even though the USA Track
& Field association changed its guidelines in April, the word hasn't
Most people still think you're supposed to drink as much as you can. But
that advice is dead wrong, says Timothy David Noakes, MD, PhD, chairman of
exercise and sports science at the University of Cape Town and the Sports
Science Institute of South Africa. An authority on endurance sports, Noakes
advises South Africa's national rugby and cricket teams. He's the author of
Lore of Running, for years a bible to many serious runners.
"People have been coached to think that dehydration is the worst thing
that can happen during exercise, so now you have a dangerous situation,"
Noakes tells WebMD. "A woman only needs to put on 2.5 kg of fluid to kill
herself. It adds up real quickly -- it is easy to get overloaded. It is
frightening how easily it can happen."
It's often said that by the time you get thirsty, you've waited too long to
take a drink. Nonsense, Noakes says.
"The idea that thirst comes too late is a marketing ploy of the sports
drink industry," Noakes says. "They tell people their thirst is not
giving them right information. There is absolutely no biological information
that is correct. The answer is just drink what your thirst dictates."
The Beginning of Bad Advice
In an editorial in the July 19 issue of the British Medical Journal,
Noakes notes that from ancient times until 1969, people didn't drink during
exercise. Then an influential -- and, Noakes says, error-filled -- scientific
paper concluded that this led to dangerous overheating. Soon after, the first
sports drinks hit the market, and advertising encouraged people to drink all
the fluids they could.
That still wasn't a problem, until amateur running became popular. Elite
athletes don't have time to drink too much. It's a totally different story when
people run/walk marathons over five hours.
"They are running so slowly they can drink all they want," Noakes
says. "There is no place outside of a pub where fluids are so available as
in a marathon in the U.S. And unlike a pub, you aren't limited by having to pay
for it. It doesn't take much to get fluid overload."
Between the Rock of Fluid Overload and the Hard Place of Dehydration
Fluid overload waters down the blood. It leads to dangerously low salt
levels -- a condition known as hyponatremia, in which the blood has too much
water and too little sodium. Brain cells absorb too much water and the brain
swells. It pushes against the skull, leading to seizures. Finally, a person
stops breathing. This is what killed a woman during the 2002 Boston
"Humans are actually designed quite well for dehydration," Noakes
says. "There is very little evidence it has any effect until one becomes
very dehydrated -- by which time your mouth is so dry, and you have such
extreme thirst, that this would never happen. You are going to find water or a
sports drink. There is no way you will be seriously dehydrated when you start a