this isn't directly related to low-carbing, but since we are all advised to both exercise and drink copious amounts of water, I thought it might interest some of you out there....
http://nytimes.com/2005/04/14/health/14water.html?hp
Study Cautions Runners to Limit Their Water Intake
By GINA KOLATA
After years of telling athletes to drink as much liquid as possible to avoid dehydration, some doctors are now saying that drinking too much during intense exercise poses a far greater health risk.
An increasing number of athletes - marathon runners, triathletes and even hikers in the Grand Canyon - are severely diluting their blood by drinking too much water or too many sports drinks, with some falling gravely ill and even dying, the doctors say.
New research on runners in the Boston Marathon, published today in The New England Journal of Medicine, confirms the problem and shows how serious it is.
The research involved 488 runners in the 2002 marathon. The runners gave blood samples before and after the race. While most were fine, 13 percent of them - or 62 - drank so much that they had hyponatremia, or abnormally low blood sodium levels. Three had levels so low that they were in danger of dying.
The runners who developed the problem tended to be slower, taking more than four hours to finish the course. That gave them plenty of time to drink copious amounts of liquid. And drink they did, an average of three liters, or about 13 cups of water or of a sports drink, so much that they actually gained weight during the race.
The risks to athletes from drinking too much liquid have worried doctors and race directors for several years. As more slow runners entered long races, doctors began seeing athletes stumbling into medical tents, nauseated, groggy, barely coherent and with their blood severely diluted. Some died on the spot.
In 2003, U.S.A. Track & Field, the national governing body for track and field, long-distance running and race walking, changed its guidelines to warn against the practice.
Marathon doctors say the new study offers the first documentation of the problem.
"Before this study, we suspected there was a problem," said Dr. Marvin Adner, the medical director of the Boston Marathon, which is next Monday. "But this proves it."
Hyponatremia is entirely preventable, Dr. Adner and others said. During intense exercise the kidneys cannot excrete excess water. As people keep drinking, the extra water moves into their cells, including brain cells. The engorged brain cells, with no room to expand, press against the skull and can compress the brain stem, which controls vital functions like breathing. The result can be fatal.
But the marathon runners were simply following what has long been the conventional advice given to athletes: Avoid dehydration at all costs.
"Drink ahead of your thirst," was the mantra.
Doctors and sports drink companies "made dehydration a medical illness that was to be feared," said Dr. Tim Noakes, a hyponatremia expert at the University of Cape Town.
"Everyone becomes dehydrated when they race," Dr. Noakes said. "But I have not found one death in an athlete from dehydration in a competitive race in the whole history of running. Not one. Not even a case of illness."
On the other hand, he said, he knows of people who have sickened and died from drinking too much.
Hyponatremia can be treated, Dr. Noakes said. A small volume of a highly concentrated salt solution is given intravenously and can save a patient's life by pulling water out of swollen brain cells.
But, he said, doctors and emergency workers often assume that the problem is dehydration and give intravenous fluids, sometimes killing the patient. He and others advise testing the salt concentration of the athlete's blood before treatment.
For their part, runners can estimate how much they should drink by weighing themselves before and after long training runs to see how much they lose - and thus how much water they should replace.
But they can also follow what Dr. Paul D. Thompson calls "a rough rule of thumb."
Dr. Thompson, a cardiologist at Hartford Hospital in Connecticut and a marathon runner, advises runners to drink while they are moving.
"If you stop and drink a couple of cups, you are overdoing it," he said.
Dr. Adner said athletes also should be careful after a race. "Don't start chugging down water," he said.
Instead, he advised runners to wait until they began to urinate, a sign the body is no longer retaining water.
The paper's lead author, Dr. Christopher S. D. Almond, of Children's Hospital, said he first heard of hyponatremia in 2001 when a cyclist drank so much on a ride from New York to Boston that she had a seizure. She eventually recovered.
Dr. Almond and his colleagues decided to investigate how prevalent hyponatremia really was.
Until recently, the condition was all but unheard of because endurance events like marathons and triathlons were populated almost entirely by fast athletes who did not have time to drink too much.
"Elite athletes are not drinking much, and they never have," Dr. Noakes said.
The lead female marathon runner in the Athens Olympics, running in 97-degree heat drank just 30 seconds of the entire race.
In the 2002 Boston Marathon, said Dr. Arthur Siegel, of the Boston Marathon's medical team and the chief of internal medicine at Harvard's McLean Hospital in Belmont, Mass., the hyponatremia problem "hit us like a cannon shot" in 2002.
That year, a 28-year-old woman reached Heartbreak Hill, at Mile 20, after five hours of running and drinking sports drinks. She struggled to the top. Feeling terrible and assuming she was dehydrated, she chugged 16 ounces of the liquid.
"She collapsed within minutes," Dr. Siegel said.
She was later declared brain dead. Her blood sodium level was dangerously low, at 113 micromoles per liter of blood. (Hyponatremia starts at sodium levels below 135 micromoles, when brain swelling can cause confusion and grogginess. Levels below 120 can be fatal.)
No one has died since in the Boston Marathon, but there have been near misses there, with 7 cases of hyponatremia in 2003 and 11 last year, and deaths elsewhere, Dr. Siegel said. He added that those were just the cases among runners who came to medical tents seeking help.
In a letter, also in the journal, doctors describe 14 runners in the 2003 London Marathon with hyponatremia who waited more than four hours on average before going to a hospital. Some were lucid after the race, but none remembered completing it.
That sort of delay worries Dr. Siegel. "The bottom line is, it's a very prevalent problem out there, and crossing the edge from being dazed and confused to having a seizure is very tricky and can happen very, very fast," he said.
Boston Marathon directors want to educate runners not to drink so much, Dr. Siegel said. They also suggest that runners write their weights on their bibs at the start of the race. If they feel ill, they could be weighed again. Anyone who gains weight almost certainly has hyponatremia.
"Instead of waiting until they collapse and then testing their sodium, maybe we can nip it in the bud," Dr. Siegel said.
too much water?
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