Runners' lore doesn't hold water

High intake of fluids can be deadly during exercise, doctors warn

By Gina Kolata

April 14, 2005

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 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.

LAURA EMBRY / Union-Tribune

Runners passed by a water station at the Rock 'n' Roll Marathon in San Diego in 2003.

New research on runners in the Boston Marathon confirms the problem and shows just how serious it is.

The research, reported today in The New England Journal of Medicine, involved 488 runners who participated in the 2002 Boston Marathon. The runners gave blood samples before and after the race. While most were fine, 13 percent or 62 of them 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 a sports drink so much that they actually gained weight during the race.

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 or in the hospital.

In 2003, USA Track & Field, the national governing body for track and field, long-distance running and race walking, changed its guidelines to warn against excessive intake of liquids. Marathon doctors say that 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 will be held Monday. "But this proves it."

Hyponatremia is entirely preventable, Adner and others said. During intense exercise, the kidneys cannot excrete excess water. But 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.

The marathon runners were simply following what has long been conventional advice: Avoid dehydration at all costs.

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 in South Africa.

"Everyone becomes dehydrated when they race," Noakes said.

Hyponatremia can be treated, 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.

However, he said, doctors and emergency workers often assume the problem is dehydration and give intravenous fluids instead, sometimes killing the patient. Noakes and others advise testing the salt concentration of a sick athlete's blood before starting 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.

Adner said athletes also should be careful when a race is over. He advised runners to wait until they start to urinate before drinking any more fluids.

The paper's lead author, Dr. Christopher S.D. Almond, a cardiology fellow at Children's Hospital in Boston, 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.

Until recent years, 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.

The lead female runner in last year's Summer Olympics in Athens, running in 97-degree heat, Noakes noted, spent 30 seconds of the entire race drinking.

Dr. Arthur Siegel, a member of the Boston Marathon's medical team, said that the hyponatremia problem "hit us like a cannon shot" in 2002.

That year, a 28-year-old woman reached mile 20 after five hours of running and drinking sports drinks. Feeling terrible and assuming she was dehydrated, she chugged 16 ounces of the liquid.

"She collapsed within minutes," 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. Levels below 120 can be fatal.)

No one has died since in the Boston Marathon, but there have been near fatalities there and deaths elsewhere, with seven cases of hyponatremia in 2003 and 11 last year, Siegel said. He added that those were just the cases among runners who came to medical tents seeking help.

In a letter, also published today in the journal, doctors describe 14 runners with hyponatremia in the 2003 London Marathon 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 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.

To deal with hyponatremia, Siegel said, Boston Marathon directors want to educate runners to not drink so much. 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," Siegel said.