(Reuters Health, 2003)

Marathon Dilemma: How Much Water is Too Much?
By Natalie Engler

BOSTON - Today, as Boston Marathon runners push their sinewy bodies over "heartbreak hill" and dash past throngs of cheering fans, many will do something unusual: stop and step on a scale.

The scales, positioned in Red Cross stations every mile throughout the second half of the course, have nothing to do with an obsession with being svelte. Rather, they are part of a new push to protect runners from hyponatremia, a rare condition that claimed the life of a healthy 28-year-old woman who collapsed during last year's race.

Only a handful of people have died from the condition, in which their blood sodium concentration falls to an abnormally low level, usually from drinking too much water. But the risk of suffering from its symptoms during a marathon is higher than most people think.

Dr. John Cianca, medical director for the Houston Marathon and a sports medicine physician from Baylor College of Medicine, said that over the past five years he has seen close to 80 cases of moderate or mild hyponatremia.

Moreover, in clinical studies, he and his team of researchers discovered that almost 85 percent of the subjects had lowered blood sodium levels during or after running a marathon. Nearly 25 percent had levels below 135 milliEquivalent (mEq) per liter of blood, the point at which a diagnosis is made (136-142 is considered normal).

He and his colleague, Dr. Joseph Chorley, presented their latest findings here at the American Medical Athletic Association's 32nd annual sports medicine symposium.

Hyponatremia presents a particularly vexing problem for runners and race medical staff, because many of its symptoms -- throbbing headache, nausea, cramps, and dizziness -- mirror those of dehydration.

But the standard treatment for dehydration, pushing fluids by mouth or intravenously, can prompt the brain or the lungs to swell, which can produce seizure, coma and death in a person who is severely hyponatremic.

Instead such a person should receive an IV with a concentrated sodium solution, a diuretic medication to speed water loss, and an anti-convulsive medication, in case of seizure, according to Cianca.

In more moderate cases, he added, doctors should simply restrict fluids and encourage salt consumption and wait for the person to "pee off" the extra fluid.

Houston Marathon Studies

In an effort to protect marathon runners, Cianca and his colleagues have been studying the condition in Houston since 1999. Over that time period, they recruited a total of 110 volunteers.

They tested the runners' blood, measured their fluid consumption, weighed them, and asked them to fill out questionnaires. Then they developed a model to estimate the amount of fluid and sodium they lost, and to approximate their total body sodium.

They found that runners with lowered blood sodium drank more and tended to retain more fluid than their non-hyponatremic counterparts.

That's why comparing a person's pre-weight with their weight along the course of a marathon can help determine when it's time to stop drinking.

The hyponatremic runners in the study also lost more total body sodium and had saltier sweat than their peers, according to the researchers' estimates, leading them to believe that there may be other factors that cause some runners to retain fluid or lose more sodium.

Women lost less weight and lost more sodium than men, which may help the researchers begin to explore why hyponatremia afflicts women more often than men, said Cianca.

The investigators also were able to tease out a few symptoms that help differentiate hyponatremia from dehydration.

While dehydrated runners tend to have increased heart and respiratory rates and lowered blood pressure, people with hyponatremia have normal vital signs, at least in its initial stages. They are also more likely to vomit and become puffy, but otherwise feel better than people with dehydration, he said.

How Much is Too Much?

If you're a marathon runner, what can you do to protect yourself? The standard advice is to avoid guzzling more water than you lose in sweat. But this may be easier said than done.

Not only is it hard for an individual to measure these factors, some people can become hyponatremic without drinking excessively. Dr. Randy Eichner of the University of Oklahoma Medical Center said he has seen this happen in dehydrated athletes who exercise for more than five hours.

Ironman triathletes and ultramarathon runners are particularly at risk, because of the length of their events. But slower, less experienced marathon runners also need to be especially careful.

Dr. Arthur Siegel, director of internal medicine at McLean Hospital , a Harvard-affiliated psychiatric hospital, offered a theory to explain phenomenon.

Siegel, who has been testing blood samples from American Medical Athletic Association runners for more than two decades, analyzed the blood from the 28-year-old and another young woman, who died after dropping out of the Marine Corps Marathon . Both died of brain swelling from water intoxication.

He found that they died, not just from drinking too much water, but because their kidneys stopped excreting water as a response to skeletal muscle injury.

When runners "hit the wall" they force their muscles to continue to exercise even after they've run out of glycogen, or fuel, he told Reuters Health in an interview. This triggers a stress hormone in the brain to tell the kidneys to halt water excretion, in an effort to maximize blood volume.

When this happens, even a relatively small amount of fluid can cause the brain to swell. If a person continues to consume fluids, the body reacts to the inflammation by continuing to protect blood volume, making the brain swell even more.

For this reason, Siegel believes a runner cannot become hyponatremic by over-drinking before a race. It's when they drink excessively during and after the race -- once the muscle injury has begun -- that they get into trouble.  

What to Do?

So, how is a marathon runner supposed to strike the perfect balance between drinking too much and too little?

If you run for more than five hours, weighing yourself periodically is a good idea. If you gain weight, stop drinking.

In addition, know how you sweat. Are your clothes soaked one mile into the race? Is your skin caked with white grit at the finish line? So-called "salty sweaters" are particularly at risk for over-drinking.

Watch out for feelings of confusion, nausea, fatigue, and particularly vomiting and swollen hands and feet. If you experience these, seek medical help.

Whether salty snacks and sports drinks help remains a subject for debate.

In 2002 Cianca and his colleagues gave 17 runners a sodium-supplemented drink, in addition to what they would normally drink. They also recruited a "control" group of 14 people who drank just the usual sports drinks. They found no significant difference between the two groups' blood sodium concentration, weight gain or loss or amount of fluid.

Siegel sounded a cautionary note. Hyponatremia is caused by water retention, not just sodium loss, he told Reuters Health. Therefore, it is dangerous for runners to assume that as long as they drink sports drinks instead of water they will be safe.

The bottom line is to become "more sophisticated" urged Cianca.

"The process starts six to eight months before the race. Too many people think they can participate in a marathon because someone said they could." But you have to know how your body will respond in a variety of conditions. "It's not something you should take lightly."

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