Hyponatremia

While dehydration can be dangerous, the danger from Hyponatremia is far greater. Hyponatremia is where the sodium (salt) levels in the blood becomes too dilute.

Contents

1 Symptoms

Initial symptoms tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. More severe symptoms are caused by a swelling of the brain (cerebral edema) including nausea, vomiting, headache and malaise . The link between Hyponatremia and Cramps is not clear, but there is evidence that increased sodium intake can alleviate the problem.

2 Causes

The cause of Hyponatremia is poorly understood, but there appear to be two likely causes in runners.

1. Excessive water intake can cause 'dilutional Hyponatremia'. Healthy kidneys can excrete about 2 pints (1 liter) of fluid per hour, but this may be reduced by exertion or illness . So drinking >6 pints in 4 hours could easily exceed the kidneys capacity to cope. The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" , combined with a general concern about salt intake.
2. For ultrarunners, I would argue that Hyponatremia is more likely to be caused by a insufficient electrolytes combined with appropriate drinking.

3 Likelyhood

Hyponatremia can be common in endurance athletes:

• In a 1997 Ironman triathlon, almost 4% of competitors received attention for Hyponatremia .
• In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, and 0.6% had critical Hyponatremia .

4 Risk Factors

The study revealed that the risk factors for Hyponatremia in marathons include

• A slow finish time (>4 hour)
• Consumption of >6 pints (3 liters) of water during the race
• BAA suggests a 'slight build' is also a risk factor

5 Preventing Hyponatremia

The key to preventing Hyponatremia is to ensure adequate electrolyte intake and to drink when thirsty. See Practical Hydration.