What is hyponatremia?

Excessive amounts of plain water may disturb the fluid and electrolyte levels in the body leading to hyponatremia. Overhydration when combined with prolonged endurance exercise can develop dangerously low sodium levels in the blood, less than 135 millimoles per liter (normal plasma sodium concentration is 136-142 millimoles per liter). Osmotic balance across the blood brain barrier is disturbed due to the continuous fall of sodium concentration leading to rapid entry of water into the brain. This can lead to serious list of complications like cerebral edema, serious neurological responses like seizures, confusion or coma and even death due to ruptured brain stem.

Decrease in serum sodium concentration is directly proportional to the speed and degree – more rapid and higher fall, higher the risk of severe consequences of hyponatremia.

Symptoms of hyponatremia

Early symptoms of hyponatremia include headache, puffiness, muscle cramps, slurred speech, nausea and vomiting, these are experienced when plasma sodium levels fall below 130 millimoles per liter. With increased severity, sodium concentration below 125 millimoles per liter cerebral edema, altered mental status like confusion, disorientation, seizures, respiratory distress due to pulmonary edema, coma or even death can occur. Sodium levels should be checked when an athlete complains acute symptoms of hyponatremia and the athlete should not be rehydrated even on claims of thirst as this might worsen the situation.

Causes of hyponatremia

During a high intensity long duration exercise, sodium is lost in sweat. Moreover drinking too much water can cause water retention, further diluting the sodium levels in the body. Hyponatremia is primarily caused when the water intake exceeds the amount of sweat and urinary losses. It is very important to prevent hyponatremia as it is more often self-induced. Hyponatremia has no association with low sodium diet or any nutritional deficiency; it is purely due to excessive intake of water combined with high intensity long duration exercises.

Preventing hyponatremia

It is prudent to avoid over consumption of fluids and have sports drink or other salty foods rather than just emphasizing on plain water.

Salt intake can be increased several days prior to an event, provided you are not suffering from hypertension.
To prevent loss of sodium before an event, an athlete should avoid overhydration. Maintain a high degree of self-discipline and learn not to exceed water consumption more than the sweat loss.
Follow a thumb rule for high intensity long duration exercises - 1 cup fluid for every 20 minutes.

Submitted on January 16, 2014