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Training Tips/Resources - Hydration vs. over-hydration (hyponatremia)

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Forum -> Training Tips/Resources -> Hydration vs. over-hydration (hyponatremia)
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kwiley

Posts: 940

Posted: Thu Aug. 09, 2007 12:29 pm
Hot enough for you? Most of the northern hemisphere is baking right now and the heat is putting extra demands on daily rides.

Hydration is a key concern in high temperatures. A roadie can easily sweat off several pounds of water weight on a three-hour ride, making it imperative to keep chugging down liquids.

Right? Maybe not. When it comes to hydration there can definitely be too much of a good thing.

That caution comes from Lulu Weschler, a physical therapist and long-distance cyclist. In 2005 she authored the summary of the first International Exercise-Associated Hyponatremia Consensus Development Conference in Cape Town, South Africa. In October she'll fly to New Zealand for the next session.

The key word: hyponatremia. It describes a dangerous condition caused by over-hydration -- drinking to the point where sodium levels in the blood become so low a medical crisis is at hand (see below).

Dehydration is bad, but hydrating to the point of hyponatremia can be deadly.

Here's the scary thing: Hyponatremia can occur even when drinking seemingly reasonable amounts. To explain, we're turning this over to Ms. Weschler, who has written extensively about the malady. At the end we'll provide the link to a more detailed article she wrote for the UltraMarathon Cycling Association website.

LESSONS FROM LULU

Every serious case (including deaths) of hyponatremia thus far reported during or after exercise has involved over-hydration. Sodium is lost during exercise and that's a concern, but by far the dominant factor in exercise-related hyponatremia is excessive fluid intake.

Some cyclists assume they're safe because they're drinking sports drinks with electrolytes. However, a sports drink has a much lower concentration of sodium than blood. Thus, drinking too much sports drink can dilute blood sodium to a dangerous level, just like drinking too much water.

Salty snacks and/or salt capsules do not necessarily protect you from hyponatremia if you are overdrinking.

Hyponatremia means that when you divide the amount of sodium by the volume of blood plasma, the number you get is too small. This number is called plasma sodium concentration. (Hypo means too small; natremia means sodium status.)

Theoretically, there are two ways to make the number too small: (a) by decreasing the amount of sodium, or (b) by increasing the volume of fluid. Thus far, in exercise-related hyponatremia cases studied, there has always been increased volume of water. (We do not know to what extent sodium loss was a contributor to the illness.)

Fatal Brain Swelling

Over-hydration all by itself (regardless of whether or not sodium is "washed out") can cause hyponatremia simply by diluting sodium. When the dilute blood gets to the brain, water seeps into brain cells and causes swelling. In hyponatremia deaths, brain swelling is the killer.

Over-hydration during exercise can happen not only when you grossly over-drink, but also when you are moderately over-drinking and retaining the overload that you would urinate at rest.

Take seriously any sign that you are putting on water weight during a ride.

Weighing yourself before and after a ride is a good way to sort out hydration needs. You should never finish with a weight higher than when you started.

Other signs of over-hydration include bloating -- puffiness in the hands or feet (at the sock line, watch, rings) or at the shorts line; "boggy" feeling flesh; headache (especially noticeable when you ride on a bumpy road); and looking like or feeling like the Michelin Man.

Early Signs

Nausea and vomiting are often seen early in the development of hyponatremia.

Since it's the brain swelling that kills, signs of weight gain plus any change in mental status (confusion, memory loss, disorientation) or any neurological symptom (uncoordination, slurred speech) are a clear indication of hyponatremia and represent a dire medical emergency.

What to do? Stop drinking.

You want urination to dump the fluid overload. A strong dose of salt could help get urination started. The medical staff at the Boston Marathon uses concentrated bouillon, one bouillon cube per ounce of water. This is the one exception to the no-drinking rule -- you need a delivery vehicle for salt. Other remedies include V-8 or tomato juice to which salt is added. Find a way to get salt in. Then wait eagerly to start urinating.

Do not drink sports drink (unless a significant amount of salt is added). The concentration of sodium is way too low and the additional fluid will make the situation worse. Do not resume drinking until you are certain that you have gotten rid of the fluid overload.

Not What It Seems

Sometimes over-hydration is counterintuitive. For example:

---"I'm drinking a reasonable amount, not a huge amount. Why am I going bloaty?" (You can retain a water overload during exercise that you would normally urinate at rest.)

---"I haven't urinated for a long time. Doesn't that mean I am dehydrated and need to drink more?" (No! not if you are retaining water.)

---"Isn't this just an issue of sodium intake? Won't I be okay if make sure to keep up my salt intake?" (No! not if you over-drink.)

To prevent hyponatremia, think first about not drinking too much. A distant second is increasing salt intake.

These are two misconceptions I often hear:

---"I'm hot and sweaty and I feel crappy. It must be because I'm not drinking enough."

Not necessarily. You can be perfectly well hydrated and be generating more heat than your body can dump, so it warns you by making you feel bad. In other words, when it's hot and you feel poorly, it may well be because it is hot.

---"Hydration is the most important thing, so I'll continue drinking. But to prevent hyponatremia I'll take in more salt."

We have seen people who are way over-salted and have, as a result, stored fluid. Secondly, some people think that if they chug a sports drink instead of water they will be fine. But again, if you over-drink a sports drink you will go hyponatremic almost as fast as if you over-drink water.

The best hydration strategy: "Drink to thirst, salt to taste."

In other words, don't force anything. Listen to your body.
 
"If you brake, you don't win." Racer Mario Cipollini
Forum -> Training Tips/Resources -> Hydration vs. over-hydration (hyponatremia)
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