Hydrofatality! - The Science and Culture of Excess Fluid Consumption
Ah, precious, nurturing water: so fundamental to our existence, so synonymous with life in all its forms. Our bodies are around 60% water; you may have heard higher figures, but the fact that this number is often inflated is evidence of the degree to which our culture is obsessed with hydration. To ensure our health, we are often told it is necessary to consume at least 8-10 glasses a day. We are even taught to mistrust our own thirst; thirsty or not, we are told, one should “push” water during exercise or when outside in the heat. Where convenience stores used to have one or two brands of bottled water, there are now shelves lined with dozens of different varieties; some advertise the purity of their contents: “Fiji Water never meets the compromised air of the 21st century!” while others advertise their embellishments: caffeine, vitamins, taurine, selenium. Of course, hydration is not just a fad – water is, in fact, crucial to our existence. But there are limits, however rarely breached, to water’s beneficial effects. Even venerable Hippocrates recognized that “everything in excess is opposed to nature,” and water is no exception.
If you’ve been paying attention to the news, you’ve probably heard about the recent death of Jessica Strange, a woman in California who died from drinking too much water in a “hold your wee for a Wii” contest sponsored by a local radio station. It may or may not have come as a surprise to you that too much water could be fatal, but it certainly wasn’t a surprise to everyone. Part of the insane tragedy of this story is that the DJs apparently ignored a number of people who called the radio station to tell them that this contest was no joke. It might be a stretch to blame the ignorance involved in this tragic event on our “if some is good, more is better” American culture, but at the very least it goes to show how hard it is for some people to get their mind around the idea that any quantity of something so necessary to life might be deadly.
On the other hand, many people have an intuitive sense of why drinking lots of water might be bad for you: because it dilutes your, you know…stuff. The fact is, if by “stuff” you mean sodium, that’s a pretty good start toward explaining how water can be deadly. Generally, American diets are high in sodium, and we often hear TV docs saying that it is good to cut down your sodium intake, that too much salty food is bad for you, and therefore as a rule, the less salt the better. But despite its bad rap in our culture, sodium is just as essential to life as water. If we’re talking canned soup, “30% less sodium” might mean that it’s good for you, but when we’re talking bodily fluids, a reduction in sodium concentration of just a couple percent can have devastating effects. This is especially true in the heart and brain, which rely on the maintenance of sodium concentrations for their normal functioning.
When the body is inundated with water, hyponatremia (abnormally low sodium) can result, and in extreme cases, the brain swells like a balloon inside the skull, producing confusion, dizziness, nausea, coma, and in extreme cases, death; a constellation of symptoms that together are known as “water intoxication.” To understand why this dangerous swelling occurs, it’s important to understand something about the salt and water economy in the body.
Under normal conditions, the body is as meticulous as a freshman designing a Myspace page about keeping the balance of salt and water just right. Water can move relatively freely between the insides and outsides of cells; typically about two thirds of the water in your body is located inside cells and the other third is located in the circulating fluids outside of the body’s tissues. Sodium, on the other hand, is highly concentrated in the extracellular fluid, ensuring that intracellular and extracellular fluids have about the same amount of “stuff” dissolved in them, and keeping the net movement of water across cell membranes to a minimum. In the case when you have, for example, maybe ingested a pound of rock salt or five gallons of tap water, it’s not hard to imagine this delicate balance being thrown entirely out of whack. In the latter case, the extracellular fluid can become more diluted than the intracellular fluid, causing the cells in organs like the brain to quickly soak up excess water like sponges, expanding in the process.
If identified quickly, even severe cases of acute water intoxication can be treated relatively easily. As you might expect, the condition can be rapidly reversed by the intravenous administration of hypertonic saline (basically just extra-salty water). For those of you do-it-yourselfers out there, it’s worth pointing out that just drinking a glass of saltwater is not recommended, because the absorption of sodium through the stomach is not terribly efficient. Plus, if the two gallons of water in your stomach haven’t made you nauseous already, drinking a cup of saltwater might. One of the little ironies of water intoxication is that nausea is an extremely potent inhibitor of urination, so urination is actually inhibited in one of the cases where you need it most. Substituting sports drinks for water won’t keep you out of trouble either, since sports drinks actually contain only about one tenth of the sodium concentration that you need. There is absolutely no evidence that Gatorade is better than water with regard to the risk of hyponatremia.
So how much fluid does it take to get into the danger zone? Jennifer Strange, the woman who died in the radio contest, drank an 8 or 16 ounce bottle of water every 10-15 minutes, totaling 224 ounces or almost two gallons of water in a couple hours, a number that’s probably at the low end of the potentially deadly range. In fact, given the large quantities of water involved, cases of fatal water intoxication are relatively rare. The first recognized human case wasn’t described until 1935, although the phenomenon was observed in animals a number of years earlier. Curiously enough, the 1935 fatality wasn’t due to excessive drinking, but was instead a consequence of (and I quote) “the administration of nine liters of tap water by rectum.”
Although excessive thirst and other disorders of water maintenance can occur in some forms of diabetes and other diseases, death by water often seems to involve the same peculiar mix of insanity, tragedy, and ignorance embodied in the case of Jessica Strange. Before the latter quarter century, cases of compulsive water-guzzling and the resulting mal effects were restricted almost exclusively to psychiatric wards. Patients attempting to “’wash out parasitic worms’, to ‘keep the body pure’, and to ‘cleanse the body of sins’” have been observed to ingest up to 10-20 liters of water in a day. In recent decades, however, there have been a number of fatal cases of hyponatremia in two other less obviously at-risk populations: endurance runners and U.S. Army recruits.
In a 1982 Army brief entitled “Water as a Tactical Weapon: A Doctrine for Preventing Heat Casualties,” the authors observe that “In the past, training and field exercises have often resulted in significant heat injuries.” In an attempt to combat dehydration, sometime during the late 1980s the US Army adopted aggressive new recommendations for water consumption, recommending in some cases up to 2 liters per hour during strenuous exercise. As a result of these new guidelines, between 1989 and 1996 there were some 125 reported cases of hyponatremia of varying severity, including several deaths. As might be expected, almost three quarters of the cases occurred in the first month of basic training. Ironically, in a number of the fatal cases, initial symptoms of headache and nausea were interpreted (by officers, medical staff, or the soldiers themselves) as symptoms of dehydration, resulting in the even more aggressive consumption or intravenous administration of fluids, with dire consequences. Sergeants at Fort Benning, Georgia must have been especially zealous about making their soldiers finish their canteens, as that camp alone accounted for almost 40% of the cases. After a number of years of mounting evidence that their guidelines were at fault, the military finally issued revised recommendations for fluid intake in 1998, causing the number of reports of hyponatremia to decline quickly and significantly.
The rise of hyponatremia in endurance athletes is also a story of changing cultural practices and institutional policies. Although the links between policy and practice for distance runners are less explicit than for US Army privates, several authors seem to agree that sometime in the 1970s there was a shift in consensus about the amount of fluid it was healthy for endurance athletes to ingest during exercise. Before this time, athletes were told to avoid drinking while exercising at the risk of sacrificing performance. But at some point this advice changed, and by the 1980s athletes were often being advised to actively push fluids before, during, and after exercise to avoid performance-sapping dehydration.
Around this time, the first cases of hyponatremia in long-distance runners began to be reported. Despite clear evidence that overdrinking was a real and present danger for athletes competing in long-distance events, the incidence of hyponatremia continued throughout the ‘80s and ‘90s, and into the new millennium. In three high-profile cases – one in 1998 and two in 2002 – athletes (two of them doctors) succumbed fatally to hyponatremia after completing marathons in the U.S. In 2005, a large study published in the influential New England Journal of Medicine reported that of almost 500 runners studied immediately following the Boston Marathon, 13% had mild to moderate hyponatremia, and .6% had critical hyponatremia. If those numbers are accurate, it means that approximately 2000 people cross the finish line with some form of hyponatremia, and of those, nearly 100 are severely overhydrated. The most likely candidates for overhydration are less-experienced runners who, because they are running slowly, drink a larger amount of liquid over a longer period of time.
In addition to demonstrating that the incidence of hyponatremia in long-distance runners is much higher than you might expect, these large scale studies indicate that the relationships between overdrinking, hyponatremia, and water intoxication are complex. Not everyone who drinks too much fluid develops hyponatremia, and not everyone with hyponatremia develops the symptoms of water intoxication. This complexity most likely reflects individual differences in water and sodium maintenance, as well as other factors such as the timing and amount of fluid consumed, diet, overall fitness, and recent drug use (some over-the-counter pain relievers interact with the body’s mechanisms for maintaining water balance).
So why is it, one might ask, that the military – never an institution especially known for its ability to make swift policy changes – was able to dramatically reduce the cases of water intoxication in a relatively short number of years, while many endurance athletes remain apparently unaware of the dangers of fluid over-consumption even today? T.D. Noakes, a doctor of sports medicine in South Africa and one of the authors on the first publication describing endurance event-associated hyponatremia, thinks he knows the answer, and he’s not shy about making it heard. In a 2003 British Medical Journal editorial, he linked the rise in overconsumption of fluids by athletes to the growing sports drink industry. Gatorade took notice – the same day the editorial was published, they posted a rebuttal on the web site of the Gatorade Sports Science Institute, advising that the editorial was “best portrayed as one man’s opinion.” In a subsequent 2006 article entitled “Case proven: exercise associated hyponatraemia is due to overdrinking. So why did it take 20 years before the original evidence was accepted?”, Noakes pointed out that in 1996, around the same time that the Army was considering making its own hydration guidelines more conservative, the American College of Sports Medicine modified its recommendations towards the other extreme – to encourage athletes to drink “as much as tolerable” during exercise. He also points out that the ACSM’s only “platinum” sponsors are Gatorade and the Gatorade Sports Science Institute.
Whether or not there’s some larger conspiracy afoot, there’s no doubt that everyone “knows” about the performance costs and dangers of dehydration largely through the efforts of companies that make money quenching your thirst. Unfortunately, our intuitions about what’s good for us aren’t infallible, but are rather built out of a confounding mix of instinct, evidence, and advertising. Whether we’re drinking ourselves to death because we were ordered to, in order to finish a marathon, or to acquire the newest gaming system, the human animal’s ability to carry even our most basic needs to excess is surely our own particular brand of insanity.
References
Gardner JW. 2002. Death by water intoxication. Military Med. 167(5): 432-4.
Rabiner CJ, Saravay SM. 1974. Water intoxication and food faddism. Psychosomatics 15(3): 113-4.
Rowntree LG. 1923. Water intoxication. Arch Intern Med. 32: 157-74.
Rowntree LG. 1922. The Water Balance of the Body. Physiol Rev. 2(1): 116-69.
Rosner MH, Kirven J. 2007. Exercise-Associated Hyponatremia. Clin J Am Soc Nephrol. 2: 151-61.
LD50
Scientific knowledge can be a scary thing. It’s often said that doctors are the worst hypocondriacs, because once you get under the hood, it’s easy to see all the ways things can break down. Likewise, the more you know about what’s out there in the world, the less auspicious a place it seems for small, soft, and pink critters like us. In this column, we explore interesting corporeal glitches and Mother Nature’s sometimes viperous disposition. Just remember: science doesn’t kill people, but, um…lots of things do.
3.05.07 - “A Pill to Take or Not to Take” by Robert Roose, MD MPH