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.

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 commonly believed to be related to excessive water intake . However, I would argue that Hyponatremia is caused excessive fluid intake in the absence of sufficient electrolytes. 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 .

3 Risk Factors

The study revealed that the risk factors for Hyponatremia 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.

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.