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As the heat and humidity of summer roll into most parts of the country,so will the admonitions to runners to be "well hydrated." "Drink as much as possible" has been the standard instruction given at races nationwide in the face of a rising mercury. However, growing understanding of a condition known as hyponatremia, which is characterized by low blood sodium, is beginning to cause physicians to reconsider the time-tested hydration advice for runners on race courses for more than four hours. Race medical personnel have been seeing—and recognizing—more and more cases of the condition, and it has become clear that telling runners to drink as much as possible before, during, and after long races in hot weather may not be the best advice. Rather, race medical personnel are beginning to focus on cautioning runners not to drink too much, and on what runners should drink.
Hyponatremia occurs when the body becomes "flooded" with water, thereby diluting the electrolytes and causing an imbalance. In severe cases the person can develop seizures and drop into a coma. Cases of hyponatremia at road races have occurred predominantly in marathons among people finishing in 4 hours or slower. The numbers of participants running at that pace has grown substantially over the last ten years, with a concomitant slowing in average marathon times. These slower runners are on the course for a long time; tend to slow down enough—or stop—at aid stations to actually drink from the cup, rather than just grabbing a couple small gulps while trying not to break stride; and often carry their own fluid supply to sustain them between water stops. The result is a significantly increased incidence of hyponatremia.
The potentially serious consequences of hyponatremia have caused race medical staffs to learn more about it, and to begin to change the information they give to runners on hydration. Dr. Bill Roberts, Twin Cities Marathon Medical Director, notes that blanket advice for all runners on hydration ignores the fact that people have highly varying fluid replacement needs, so races should encourage runners to try to learn more about their own individual requirements.
"Fluid replacement is sweat rate dependent, and sweat rates vary considerably from athlete to athlete, ranging from just under 1 liter/hour to nearly 4 L/hr," says Roberts. Thus, instead of the blanket advice often given to drink early and often, race participants are urged to get an idea of their own sweat rates. Adjust fluid replacement accordingly, says Roberts. "1700 ml per hour of fluid replacement during activity will rapidly overhydrate a runner with a sweat rate of 800 ml per hour and underhydrate the 3.8 L/hr runner," he says.
While it's unrealistic to expect runners to find such exact measurements of fluid loss and corresponding replacement, one can get a reasonably accurate gauge through trial and error on training runs. Sweat rate will be impacted by climate as well, so experimenting in a variety of environmental conditions is recommended.
Some runners might be operating under the premise that because hyponatremia can be caused by flooding the body with water, simply hydrating with sports drinks instead of water can solve the problem. While theoretically possible, Roberts points out that most athletes tire of sports drinks at some point, switching to water, which washes down the sodium level. Moreover, if a person happens to sweat out a lot of salt, hyponatremia can still result.
"There is a population of athletes that sweat a lot of salt," says Roberts. "These athletes can, in intense exercise, lose too much salt and in the process of replacing fluid with an inadequate amount of water alone become hyponatremic."
Runners can often figure out how much salt they are losing by looking at their clothing or skin after they run. After a run, skin and/or clothing left with a white residue of excreted salt indicates a heavy loss of sodium. A small amount, especially during the early period of acclimation to heat and humidity, is not a warning sign, but large amounts of the residue excreted in all climate conditions is. These individuals need to be more careful than others of both the amount and content of their fluid replacement.
The other key element to add to race instructions is to be careful to get enough sodium, both in your diet leading up to the race and by consuming drinks with sodium during the event. Some ultra events and marathons have even begun to include chips and pretzels at aid stations to try to address the issue.
Getting extra sodium is not a guarantee against hyponatremia, however. As always the most useful recommendation is to monitor your body for signs of excess stress. Light-headedness, dizziness, headache, and nausea are early symptoms of possible hyponatremia. Usually, the individual is also "puffy" or bloated—rings on fingers are "tight," same with shoes. This is due to excess water retention. Runners should be urged not to "gut it out" or "run through" these symptoms.
It is still unclear what role hyponatremia played in the death of Cindy Lucero at this year's Boston Marathon. Lucero collapsed near the 22-mile mark about 5 hours into the race, and died two days later. She was reported to have had a low sodium reading when she was admitted to the hospital, indicating she may have been hyponatremic. An autopsy, which could help determine if hyponatremia were a cause of death, has not yet been done due to a backlog caused by budget cuts in the medical examiners office.
While marathons are beginning to recognize hyponatremia and take steps to educate runners about it, many questions remain about the condition, and more research into hyponatremia is being conducted. The causes of hyponatremia are still poorly understood. For a while it was thought that it might be a condition that only individuals who retained water—didn't excrete fluids normally—were prone to develop. However, as more research has been done, most notably by Dr. Tim Noakes in South Africa, it has been shown that "normal" individuals can overhydrate with water and become hyponatremic.
Hyponatremia vs. Dehydration
The shift by some races away from counseling runners to drink as much water as possible has led to a debate regarding the relative dangers of hyponatremia versus dehydration. Many physicians believe that telling runners not to drink as much as possible could lead to dehydration.
According to South African physician Tim Noakes, however, hyponatremia is a more dangerous condition than dehydration. "Whereas there are no case reports or clinical trials that unambiguously link exercise-induced dehydration with specific, life-threatening, exercise-related disorders, the evidence that iatrogenic fluid overload can have very serious consequences is absolute and irrefutable." Noakes wrote in the Physician and Sportsmedicine.
"How is it possible that this evidence can be so long ignored and that athletes can continue to be encouraged to ‘consume the maximum amount that can be tolerated' during exercise, without any cautionary reference whatsoever to the dangers of drinking too much? It is a scientific paradox, for which any logical explanation continues to elude me.
"Compared with this irresistible proof, the evidence is nonexistent that the modest levels of dehydration in endurance athletes—body mass losses of 2% to 8%—have any health consequences during exercise." But the common belief has been, says Noakes, that runners who collapse after a race in the heat are suffering from some heat related illness brought on by dehydration. Noakes contends that dehydration does not cause heat illness, the intensity of exercise in the heat does.
Others still worry that advising runners not to drink can be dangerous. Roberts is one who believes that the dangers of dehydration should not be ignored. "There is substantial evidence to show that dehydration has adverse affects on several systems in the body that affect heat balance and performance," he notes. "Dehydration negates the effects of acclimatization to heat and decreases sweat output, cardiac output, cardiac stroke volume, and gastric emptying; all of which increase the risk of developing hyperthermia, even in conditions that are below the usual cancellation levels."
Roberts also points out that it is possible for an athlete to become hyponatremic and dehydrated at the same time, if they happen to sweat out a lot of salt. "It is possible to lose salt and water in sweat to a degree that leaves an athlete low in salt and water. In some cases the water losses are large and dehydration is the result. Athletes drink fluids to replace the water losses and often the fluids do not contain sodium, so over time they end up with hyponatremia from a combination of salt loss and dilution from water replacement.
The amount of water is not ingested at a volume to cause overhydration. So you end up with an athlete who is dehydrated and hyponatremic. This is documented in a marathon runner in an article out of the Pittsburgh Marathon. It is most frequent in the Ironman triathlon where the winners are out for 8 hours and others can be out for as long as 18 hours."
Roberts notes that "the most likely victims of this problem may be cystic fibrosis carriers who can see 100 mEq of sodium/hour. The salty sweaters will have salt caked on their skin and in their clothing and it is easiest to see in black lycra togs."
University of Connecticut researchers Larry Armstrong and Doug Casa also feel that the dangers of dehydration should not be taken lightly. They wrote a counterpoint to Noakes' article in the Physician and Sportsmedicine warning that minimizing the impact of dehydration can have serious consequences. In short races where the intensity of the effort tends to be greater, athletes can build up dangerously high temperatures, says Armstrong, and the body is better able to deal with this heat build up if the individual is well hydrated.
Noakes agrees that it is the intensity of exercise that poses the greatest threat of heat injury, but he contends that the scientific evidence is not there to support dehydration as a significant contributor to heat injuries suffered by athletes who do compete too hard in adverse climates. Noakes takes the position that races should simply not be held when the weather conditions indicate a high probability of heat injuries, according to the ACSM (American College of Sports Medicine) guidelines. It is intense exercise in adverse weather conditions—the combination of heat and humidity—that create the danger, not the hydration status of the competitors, says Noakes. He states flatly that races simply should not be held under such conditions.
The IV Debate
Hyponatremia has also sparked debate over the use of IVs at races. Noakes adamantly believes that treating runners with IVs is often dangerous, as race medical staff may mistake a case of hyponatremia for one of dehydration, with potentially devastating effects. He states that trained medical personnel can properly determine whether or not a runner is suffering from a heat related illness, and then the proper treatment is cooling, preferably using an ice bath. Giving a runner who collapses at the finish line an IV, if that runner is hyponatremic, only makes the condition worse, says Noakes.
Some race medical directors believe, however, that an IV is the most effective way of treating athletes who are dehydrated. Noakes says that dehydrated athletes respond well to oral rehydration and don't need IVs. Twin Cities medical director Bill Roberts agrees with both sides, saying that most dehydrated runners will respond well with oral rehydration, but he notes that there are some who may require IV treatment. There is no definitive answer, but use of IVs appears to be diminishing. At the Twin Cities Marathon there have been less than 150 IV starts in the race's 20 years.
According to Roberts, the bottom line is that "fluid replacement is essential to performance. Too much fluid is bad. Not enough is bad. I think we need to send a message for the middle ground. Many of us find it naturally. Racers do not have time to ingest too much, but need a plan to take in an adequate amount to avoid the pitfalls of too little." He notes that slower marathoners have a lot of time while out on the course to drink too many fluids, and they seem to have taken to heart the standard advice to drink as much as possible, which can lead them to trouble. The race director can play an important part in educating runners on the importance of finding the middle ground, and emphasizing to the slower runners that while adequate fluid intake is important, it is possible to overdo it.
In addition, race directors should pass some of the onus of responsibility to the individual runner. Encourage runners to monitor themselves on training runs to get an idea of how much fluid they actually need to replace in a variety of weather conditions. There is no magical level of fluid replacement that fits all runners. If there is any such thing as a blanket recommendation to runners it's this, says Roberts: "Slower pace in the heat. Paced [fluid] replacement that does not exceed sweat rate. And stopping if things seem out of the norm."
This article originally appeared in the July 2002 issue of Road Race Management
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