Hyponatremia: The Dangers of Overhydration

Most  physically active individuals don’t go anywhere without the proverbial bottle of water. And most drink far more than the prescribed minimum eight glasses a day. But is it possible to drink too much water? Yes, says the medical community, noting an increasing incidence of a life-threatening condition known as hyponatremia among recreational athletes participating in endurance events and activities.

What Causes Hyponatremia?

Hyponatremia, defined as an abnormally low concentration of sodium in the blood, is being linked to illness and even death in marathons, ultramarathons as well as lengthy hiking trips and military outings. While the cause is technically unknown, an overconsumption of water and/or underconsumption of sodium is believed to increase the risk by diluting the blood. The combination of losing salt through perspiration during an endurance event combined with drinking copious amounts of water can alter the appropriate sodium concentration of your blood with potentially serious consequences.

Symptoms of Hyponatremia

Ironically, many of the major symptoms of hyponatremia are similar to those of dehydration, including:

1.  nausea and vomiting

2.  muscle weakness

3.  headache

4.  disorientation

5.  bloating and puffiness of the face and fingers

6.  seizures (in severe cases)

7.  loss of consciousness (in severe cases)

Even mild symptoms should not be ignored as some deaths have occurred hours after participants completed an endurance event.

Who’s At Risk?

“Middle-of-the-pack”, recreational athletes are more prone to hyponatremia than are elite athletes because they take hours to complete an endurance event and may be taking in too much water and/or too little sodium. For example, one victim, a 43-year-old woman, died after completing the Chicago Marathon – her first – in more than four hours. Woman, in fact, are particularly susceptible to hyponatremia. In fact, Medicine and Science in Sports and Exercise reported that approximately half of the women but only 14 percent of the men participating in the New Zealand Ironman triathlon developed some degree of hyponatremia. Researchers speculate that women may drink more water than men in relation to their body size and needs and/or they may avoid salt in their diet to prevent water retention.

Treatment and Prevention

So how much water should you be drinking to prevent dehydration but avoid hyponatremia? The American College of Sports Medicine recommends imbibing 17 ounces of fluid two hours before exercise and then drinking at regular intervals to replace water lost through perspiration. But individuals vary in their “sweat rates” so determine yours before participating in an endurance event according to the following formula. Weigh yourself before working out for a half an hour at your anticipated pace and under the climactic conditions you expect. Then weigh yourself again and for every pound you lost (yes, it’s all water) plan to drink a pint per hour during your event or activity. For further insurance, drink a sports beverage containing electrolytes at least part of the time. A recent study showed that hydrating with sports drinks helps prevent hyponatremia by replacing the sodium as well as the fluid lost through perspiration, keeping the proportion of sodium to water content of your blood balanced. Aim for between 50 and 100 mg of sodium per eight-ounce fluid serving — what you find in most commercial sports drinks. An even better choice than Gatorade and its counterparts (most of which now contain high fructose corn syrup) is Recharge, an all-natural electrolyte replacement drink available at Whole Foods and most health food stores. You can also order it in bulk on Amazon.com. I recommend the lemon flavor.

It’s also possible to become both dehydrated and hyponatremic when you try replacing the fluids you’ve lost, but because your blood sodium concentration is so low, the water you ingest isn’t absorbing as efficiently. So, in addition to drinking a lot the few days before your event consider adding a little sodium to your food. And, when participating in any endurance activity longer than four hours, ingest food or fluid containing salt as you go.

Sodium actually enhances fluid absorption and retention. Recent research from the University Medical School in Aberdeen, Scotland had 12 male volunteers ride stationary bikes while ingesting drinks of varying sodium concentrations. The researchers found that subjects urinated less when they consumed proportionately more sodium (i.e., they retained water better). Depending on your sweat rate and the weather conditions, ingesting one or two grams of salt per hour during your event should be adequate to prevent hyponatremia

 Guzzle and Shake

When training and participating in any endurance activity it’s absolutely important to hydrate – but don’t over do it. And, in addition to drinking up, reach for that salt shaker. 

Be Well,


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One Response to “Hyponatremia: The Dangers of Overhydration”

  1. Tips for Hydrating for Heated Yoga Workouts « bewellcoaching’s Weblog Says:

    […] to drink too much water without having some salt in your diet. or you put yourself at risk for hyponatremia. Recent research also suggests sodium may have a role in mood regulation – which researchers […]

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