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Drinking Too Much Water Dangerous for Runners


Anyone who is into serious exercise learns from experience that not drinking enough fluid equals less energy. Dehydration can negatively affect athletic performance because less fluid is available for the heart, muscles and joints to perform efficiently.

Over the years, athletes and recreational exercisers have become well educated about the dangers of not drinking enough fluid during exercise.

The current standard advice given to athletes is that they should not rely on their thirst, because by the time they feel truly thirsty, they are already quite dehydrated. Therefore, they should drink according to a set formula even if they are not thirsty.

Athletes have also been advised that proper hydration will prevent heat-related illnesses like cramps, exhaustion and stroke.

This line of thinking is now being challenged by scientists like Dr. Tim Noakes of the University of Capetown, South Africa and the USA Track and Field (USATF), the United States governing body of track and field, long-distance running and race walking, because of a deeper understanding of the thirst mechanism and heat illness and increasing cases of hyponatremia (low sodium level) due to over-hydration among athletes.

According to Noakes, previous studies recommended that athletes drink copious amounts of fluid because they found a link between dehydration and a rise in core body temperature.

"The sensible conclusion was that dehydration was the single greatest risk to the health of marathon runners because it would cause the body temperature to rise, leading to heat illness, including heat stroke," Noakes writes in an advisory paper for the USATF.

However, Noakes believes past studies were in error because many of them were done in laboratory conditions much hotter than those in actual races. Temperate countries hold races in spring or fall and tropical countries hold races early in the morning, so real-life race conditions are very different from the lab-simulated ones.

Noakes also points out that many of the past studies did not take into account "facing wind speed" or the cooling effect of the wind as a runner races.

Noakes says that newer scientific research has revealed that dehydration is not the major factor in hyperthermia or heat illness.

The reality is that heat stroke can occur even when the athlete is well-hydrated, because the main factors are the intensity of the race (shorter distance races like 10K runs have a higher intensity in a shorter amount of time), athletes' body mass (those with greater body mass generate more heat than lighter ones), high environmental temperatures and humidity and still wind conditions (there will be less cooling effect on the skin).

The USATF warns that "an adequately hydrated runner who is running too fast or pushing herself too hard, especially in hot and humid conditions, can fall victim to hyperthermia. It is important that athletes adjust their pace to take into consideration race conditions, slowing their pace as heat and humidity rises, regardless of how much they may be drinking."

Dr. Lewis Maharam, chair of the International Marathon Medical Directors Association (MMDA), told writer Patricia Amend of Ace Fitness Matters that "medical directors of major marathons around the world are seeing more people in the hospital from over-drinking, and even some deaths from hyponatremia."

Hyponatremia is a condition where there is too much water in the blood and too little sodium. According to Dr. Douglas Casa of the USATF, hyponatremia occurs most frequently in sports that last longer than four hours because this gives the athletes more time to drink and to lose large amounts of sodium through prolonged sweating.

But the condition can also occur in any sport when athletes drink large volumes of fluid without adequate sodium intake.

According to Casa, commercial sports drinks have a low sodium level in order to make them appetizing for the general public. Although they are preferable to plain water for endurance athletes, there is still a danger of hyponatremia if athletes drink excessive amounts.

Most at risk are the slower runners at the middle and back of the race, because they take much longer to finish than the elite runners at the front. This means that they will probably be stopping to drink at the many water stations along the course of the race.

According to Maharam, the Houston marathon is the first in the US to decrease the number of water stations to prevent runners from drinking too much. "European marathons have already done this, and we're seeing fewer problems with hyponatremia," he said to Amend.

Casa says that runners, coaches and medical staff must be well-versed in recognizing the signs of hyponatremia because if they mistake it for heat stroke, they will do more harm by giving the athlete fluid, whether orally or intravenously.

Hyponatremia can be tricky to diagnose because it mimics many of the signs of heat stroke such as nausea, vomiting, extreme fatigue, respiratory distress, dizziness, confusion, disorientation, coma and seizures.

Hyponatremia's unique characteristics, aside from low sodium levels (less than 130 mmol/L), are a progressively worsening headache, normal exercise core temperature (generally not greater than 104 degrees F), and swelling of the hands and feet, which may be noted with tight wedding bands, watches and shoes.

To prevent hyponatremia, the USATF has released new fluid replacement guidelines, which can be found in greater detail at their website (www.usatf.org).

In a nutshell, the new guidelines say that "runners should be sensitive to the onset of thirst as the signal to drink, rather than staying ahead of thirst. By being guided by their thirst, runners prevent dehydration while also lowering the risk of hyponatremia, a potentially dangerous condition increasingly seen as runners have been erroneously instructed to over-hydrate."

Since people have different sweating rates and fluid needs, runners can predetermine their individual pattern by following the step-by-step instructions of a self-test created by the USATF, which is also available at their website.

Basically, the test involves careful weighing before and after one hour of running at the intended intensity of the future race under similar environmental conditions.

The USATF says that "athletes who have not yet had the opportunity to perform self-testing should begin their races well-hydrated, indicated by clear urine, and then drink when thirsty during their races, rather than drinking constantly as some have recommended. A sports drink with sodium and other electrolytes is preferred."

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