Hyponatremia: Marathoners- Imbibing in Water, Running out of Steam, Dying???

Science reporting by the media often adds to public confusion rather than advances understanding. Research can be a puzzle with hundreds or millions of pieces, many unknown. Science reporting tends to pull out one piece of the puzzle, focus on the weird shape, the color, the edges, then often inexplicably bestow that piece with front-page significance. Building blocks of previous studies are often ignored and the complexity of trying to fit the pieces together is sacrificed for the eye-catching title.

On the front page today, (Thursday April 14, 2005) the New York Times reports "Study Cautions Runners to Limit Intake of Water" The subject of the NYT article is the research study, "Hyponatremia among Runners in the Boston Marathon", recently published in the New England Journal of Medicine (NEJM). Hyponatremia is low sodium concentration in the blood (about <135mmol/L) caused by overhydration, drinking too many fluids.

The NEJM is appropriately specific about the results, in short: hyponatremia is a risk for a very small percentage of athletes who are generally less well trained and who over-consume water and symptomatically gain weight while running. The study significantly adds to 40 years of studies on hydration. Importantly, it supports various recent studies showing that overhydration can be dangerous. This is important. Runners shouldn't drown themselves in water - literally. The study warns that more than 3 liters in 26.2 miles is excessive.

Despite the validity of the health concern, New York Times coverage of the study reads like a sensational press release for Harvard. As with most scientific studies, the article by itself is not revelatory, the evidence has been in for a while. Medical colleges have been setting up tents at the ends of marathons and publishing the same results for years. Baylor medical college published a study in January, 2003 in the Clinical Journal of Sport Medicine (Hew et al) that found hyponatremia to be a concern. Indeed the current Harvard study liberally references other studies. This fact doesn't diminish the report because it's important to be able to repeat results. But the way the New York Times presents the research can be misleading:

"Before this study, we suspected there was a problem," said Dr. Marvin Adner, the medical director of the Boston maraton, which is next Monday, "but this proves it."

The NEJM study adds to the growing body of research, but doesn't "prove" it. However there is something about hyponatremia and the increasing number of slow runners:

"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."

Doctors now diagnose the condition in extremely high numbers says the NYT:

"New 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 [NYT added this in later edition?] were in danger of dying."

Unlike the New York Times, New England Journal of Medicine study's authors didn't mention "dying". Although several deaths have tragically occurred in marathons, fewer then 1:50,000 runners die in marathons, and most of these deaths are due to cardiovascular failure. None of the racers in this study died, though coincidentally and tragically one person did die that year. No one has died in the Boston Marathon since.

Who was in danger of "dying" as the Times so dramatically reported? The New England Journal of Medicine reported that 3 runners had "critical hyponatremia". The NEJM study does not associate any specific permanent perils or death rates with any sodium concentration, so it's unclear which levels of hyponatremia are how dangerous, but "critical hyponatremia" is a medical term used for sodium concentrations of below 120mmol/L, which are potentially fatal. Different investigators can use slightly different terms but higher (more normal) levels of sodium are commonly referred to as "low" and "moderate" or "severe" hyponatremia. Apparently the other 59 of 62 runners who had hyponatremia were in less serious though unspecified states of hydration.

The New York Times indicates that ALL runners with hyponatremia will recover if they receive prompt medical intervention of intravenous sodium infusions:

"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."

So then did 62 of 488, or 12.7% ("13%") of the racers require intravenous therapy? Extrapolated to the population of Boston Marathon runners in 2004, that would mean 2159 of 17,000 who ran required intravenous therapy. This seems misleading. That many people couldn't be so severely sick without the hospitals (and probably media) being well aware of the problem.

Perhaps only the 3 most seriously affected hyponatremic runners required intervenous therapy? But something's not right. In 2004 only 11 of 17,000 runners self reported and were diagnosed with hyponatremia. It's unknown how serious these self-reported cases were, but this is ten times less (11 of 17,000 = .06%) then the .6% reported in the study. None of the 2004 Boston Marathon racers died.

It is clear then, that the "critical" status of the cohort of 3 identified in the original study can not be extended to the entire cohort of 62 who had clinically identifiable but less serious conditions. But it is not clear how many athletes are affected in races since the percentage of affected runners in the NEJM study didn't seem to be reflected at actual marathons.

The New York Times article could give many athletes the wrong idea about the dangers of over-hydration. While it is certainly a condition to guard against, dehydration is a more common occurrence. Most racers who self-report at medical stations do so for dehydration. Dehydration leads to decreased blood flow which limits the perspiration process that dissipates heat and prevents heatstroke. Dehydration loss of more then 2% of the body weight can be problematic and lead to performance detriments. While the doctor cited in the Times article knows no case of death in marathon runners due to dehydration, this does not hold for military training and sports camps.

Appropriate hydration is highly individualistic and depends on physiology, level of training, outside temperature and diet among other things. The NYT article concludes that slower runners should not over-drink;

"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."

While is true, the statement underemphasizes the physiological changes that occur during training that lead to the elite athlete being able to run with with less water.

The most news-worthy result if the Harvard study in New England Journal of Medicine is that hyponatremia happens. This is important for both runners and doctors who are treating distressed runners because it alerts both groups to the potential of this condition. However the emphasis of the New York Times article on the high prevalence of the condition and the danger of dying exaggerates the results of the study to provide an article that is shocking enough to appear on the front page of the paper.

The New York Times misconstrues the significance and results of the study. It's not clear whether this is entirely the New York Times' doing or whether the study's authors are complicit in overstating the problem and leading us to believe that this is new research, perhaps for self-promotion.

Inaccurate media portrayal of research leads to the perception that science itself is wishy-washy. Although we always need to be attentive to new research, the media exaggeration of research studies only undermines the aims of research to improve public health. The actual results aim at correcting an imbalance in *popular* though not *expert* advice. Doctors, exercise physiologists and trainers have long advocated balanced hydration.

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