Hyponatremia and the Dangers of Over-Hydration
by Wes Kisting
Every paddler has probably heard of dehydration, which results from drinking too little water during rigorous physical activity, profuse sweating, or over an extended period of time. In fact, if you've ever felt thirsty, you've experienced the earliest stages of dehydration: thirst is the first symptom which signals inadequate water intake. To guard against it, you need to take regular sips of water throughout the day, before you feel thirsty. But did you know that it can also be deadly to drink too much water?
It may sound crazy, but it's a scientific fact. Even if most people have never heard the term "hyponatremia," or its more common nickname "over-hydration," it is a real danger to people who participate in endurance-type activities, including kayakers. Although the problem is far less common than dehydration, it's still important for avid kayakers (especially long-distance racers and tourers) to educate themselves about the dangers of hyponatremia, its symptoms, and the means to prevent it.
What is Hyponatremia?
Without getting too technical with the jargon, hyponatremia (a.k.a. "over-hydration" or "water intoxication") is a condition which results from a combination of rigorous physical activity, profuse sweating, loss of body salts, and excessive water intake. Whereas dehydration has to do with too little water in the body, hyponatremia actually has to do with too little salt. This is why typically only endurance athletes are at risk. While most people who exercise intensively will snack throughout the day or eat a meal within hours of exercising, endurance athletes (marathon runners, in particular) may go long periods of time without consuming any solids or drinking anything except water. Consequently, salts which are lost as sweat are not replaced. If the problem becomes severe enough, the body can lose its ability to contain and store water properly. Over-saturated cells burst or leak into the blood stream, causing blood cells to swell due to a "water intoxication" process not unlike that which occurs when a person consumes too much liquor. As with alcohol, the onset of hyponatremia may be signalled by weakness, dizziness, and loss of consciousness. Due to the high possibility of related swelling in the brain, hyponatremia may also result in sudden collapse, coma, and death.
The major problem with detecting hyponatremia lies in the simple act of distinguishing it from dehydration, as the initial symptoms of both conditions are remarkably similar. Consequently, education is the first major defense. Without proper awareness, a misdiagnosis of hyponatremia as dehydration can result in a "treatment" (drinking more water) which actually throws fuel on the fire. Since most people know a little about dehydration, but few know anything about hyponatremia, this sort of misdiagnosis has been known to occur even among trained medical professionals. To protect yourself from making a similar mistake, you should determine whether you are at risk for hyponatremia and learn to identify its symptoms.
Demographically speaking, the candidates at highest risk for hyponatremia are long-distance marathon runners and, more specifically, women. It's not entirely clear why women are at higher risk, but it is statistically true that more women suffer from the condition than menusually middle-aged women who are running in their first long-distance marathon, during hotter seasons or in warmer climates which accelerate the sweating process. Even so, male marathon runners can suffer from hyponatremia as well. In fact, athletes of either gender, competing in any endurance-type sport are susceptible to hyponatremia. What puts marathon runners at highest risk is their rigorous exertion, profuse sweating, lack of sodium intake, and disproportionately high water intake over an extended period of time.
According to an article on WebMD, "nonsteroidal anti-inflammatory drugs (NSAIDs) such as Advil, Motrin, and ibuprofen may predispose runners [and other endurance athletes] to hyponatremia" (Feb. 16 2001). Since Acetaminophen (Tylenol) has been shown to be safe, many experts recommend taking Acetaminophen in place of other NSAIDs during participation in endurance-type activities. At the very least, you should minimize your use of other NSAIDs before and during endurance-type activities to reduce the risk of hyponatremia.
Signs and Symptoms
When hyponatremia sets in, the symptoms often match those of dehydration: weakness, faintness, shivers, shakiness, headaches, poor coordination, reduced mental acuity, poor focus or concentration, dizziness, sickness, vomiting, loss of motor control, seizures, and loss of consciousness.
The best sign that you are suffering from hyponatremia, not dehydration, is noticeable swelling around your joints and fingers, making you look as if you are retaining water (in fact, that's exactly what is happening). If your rings or your wrist-watch feel tighter than usual, this may be a sign of such swelling.
Another potential sign that you're suffering from hyponatremia, not dehydration, is that you don't feel thirsty. Of course, be aware that the mere absence of thirst does not rule out the possibility of dehydration either. Since you can be badly dehydrated without feeling thirsty, the best way to distinguish between hyponatremia and dehydration is to track your water intake throughout the day. The next few times you go paddling, pay attention to how much water you comfortably consume in a given hour, or throughout the day, and make a mental note of this consumption level as your water-consumption "norm". On an expedition, compare your daily water consumption against this norm. Assuming you don't paddle noticeably more vigorously on an extended trip, your water intake should be similar, or only slightly higher than the norm you've established. When you find yourself confronted with the symptoms of hyponatremia or dehydration, this gives you a basis for distinguishing which condition is more likely the cause. In other words, if you haven't been taking regular sips of water or consuming as much water as your established norm, then it's far more likely that you're dehydrated. If you haven't eaten anything and your water intake has been unusually excessive during the past few hours, hyponatremia is the more likely cause of the symptoms listed above.
One good way to determine whether or not you're suffering from dehydration (as opposed to hyponatremia) is to check the color of your urine. A clear or pale yellow color indicates adequate hydration, while a darker, more concentrated yellow color indicates dehydration. While crystal clear urine does not necessarily indicate that you are suffering from hyponatremia, it does generally rule out dehydration as the likely cause of any of the symptoms listed above.
So how can you prevent hyponatremia before it occurs? Reacting to the dangers of hyponatremia, some experts recommend only drinking when you actually feel thirsty; however, most experts agree that it's smarter to hydrate before you feel thirsty because thirst indicates that dehydration has already begun. Your body performs much better and recovers from the rigors of exertion faster if you "prehydrate." Having said that, don't take the prehydration philosophy to the extreme. A common rule of thumb is to drink approximately 8 fluid ounces (one cup) of water for every 20 minutes of exercise. If, like most kayakers, you're going to be engaging in sustained exercise longer than an hour, it's wise to dissolve a small amount of sugar and sodium into your water to increase your body's absorption rate and thereby aid hydration. Many sports drinks like Gatorade and Powerade already have these absorption-boosters built in, so day paddlers might just substitute a good sports drink in place of water. For expedition kayakers (who won't want to pack along a whole case of sports drinks) a more viable option is to carry packets of Kool-Aid or powdered sports drink mixes and add them to their drinking water as needed.
The good news for kayakers is that, compared to marathon running or long-distance cycling, kayaking typically requires less rigorous physical exertion and also allows easy access to snacks throughout the day. The combination of these two factors (milder exertion and occasional snacking) dramatically reduces the likelihood of experiencing hyponatremia, even if you're long-distance touring over a period of several days. Why? Because by sweating less and allowing your body to recover some of its salt reserves (via occasional snacks), the factors which contribute to hyponatremia are minimized. In terms of preventative measures, this means that you should discipline yourself to take regular (but not excessive) sips of water throughout a long day of paddling, allow yourself to rest at least a few minutes each hour, and snack on foods with moderate sodium content consistently throughout the day (an energy bar, some trail mix, a few pretzels, etc.). Whatever you do, don't try to dramatically increase your salt intake. A little salt goes a long way to prevent hyponatremia, but too much salt may put you at higher risk for hypertension. The goal is simply to help your body replace the salt it loses, but since sweat only contains about 3 grams of salt per liter, you don't need sodium-intensive snacks. Almost any snack which isn't explicitly labeled "no sodium" or "low sodium" will suffice. Also, don't skip major meals, or if you must, replace any missed meals with proportionately heavier snacking throughout the day to maintain your body's salt, carbohydrate, and nutrient reserves.
Third, pay attention to your body temperature while you paddle. If you find yourself sweating frequently or profusely, remove layers to cool yourself down, and increase your sodium intake moderately to offset any significant increase in water intake. There seems to be no established rule for determining proper sodium-to-water intake over a given period of time, but I think a reasonable target goal is to consume a small sodium-content snack (a bag of peanuts, a couple of pretzels, an energy bar, a small bag of chips, etc.) for every one liter of water you consume. During a long day of paddling (10 hours or so), I consume approximately 4 liters of water, as well as 4 - 6 energy bars (or an equivalent snack) and my typical three daily meals. Basically, I plan to consume some kind of snack or meal every two hours (preferably carbohydrate-intensive foods), but I don't deliberately add anything excessively salty to my diet. This seems to be good practice for keeping energy levels high, staving off hunger, and maintaining a decent sodium intake to compensate for increased water intake. Follow these guidelines (adjusting, as needed, for your own metabolism and body weight) and you should be fine too.
Cause for Concern, not Panic
On a final note, I should mention that all of these concerns and preventative guidelines are geared toward long-distance tourers or competitive racers, who have the potential to suffer from this comparatively rare but serious condition. If you fall in this group, just knowing about the dangers of hyponatremia goes a long way to combatting the problem, and the preventative measures I describe are relatively simple and effective. Perhaps more comforting, if you're strictly a day-paddler who only ventures out for a few hours at a time, you have little or no cause to worry about hyponatremia. Although not impossible, it would be profoundly unlikely for a recreational day-paddler to suffer from hyponatremia, as the condition generally requires a substantial decline in sodium levels and a significant increase in water intake. Practically speaking, people performing less rigorous activities over shorter periods of time (including recreational day-paddlers) generally could not consume enough water during their shorter period of activity to put themselves at risk.
[Editor's Note: This article summarizes Wes Kisting's research and findings about the symptoms and dangers of hyponatremia. Wes Kisting is not a licensed medical expert, nor claims to possess any personal medical expertise. For a more complete, in-depth understanding of hyponatremia, its symptoms, and its risks, ask your doctor to recommend additional medical-information resources, or try an advanced search on the Internet.]
© 2006, Wesley Kisting