Hyponatremia is caused by low blood sodium levels. It is also often referred to as water intoxication. It describes a condition where you have absorbed too much water in relation to your body’s electrolyte levels. The ratios are out of whack!

When sweating, even heavily for period of up to 3 hours, drinking water is normally sufficient to rehydrate our body. Regular diets typically allow us enough electrolyte reserves for this.

But for sustained heavy sweating of many hours ie an all day, multi day ride, electrolytes are probably required along with the water intake. If not, we risk Hyponatremia.

Since our sweat contains salt, we lose both salt and water. After the first several hours, our stored electrolyte levels become depleted (through sweat) and diluted (by heavy water intake).

If we continue, we eventually dilute the blood sodium below the levels required for our system to maintain balance and hinder our body’s heat regulation system.

When is a rule of thumb misleading?

The usual rule of thumb is to drink enough water in order to generate pale-colored urine on a frequent basis. The thinking goes that if you are urinating pale, you are hydrated. Normally, this is the case.

But when your blood sodium level is low, your system attempts to dump excess water through urine in an effort to prevent hyponatremia.

There is too much water showing up for duty in relation to the electrolytes available that know how to use that water. Your body is basically saying that it can’t use the water without the required electrolytes. So out it goes.

In this case, you could be urinating a lot of water, thinking that you are well hydrated but in fact becoming progressively dehydrated and dangerously close to hyponatremia.

Hyponatremia is a very serious condition. Dangerous brain swelling occurs as sodium levels are no longer sufficient to maintain cellular water balance. Medical treatment is not straightforward. You can die from it.

Note: There is evidence that ibuprofen (Advil etc) and naproxen (Aleve etc) can enhance susceptibility to hyponatremia when water intake is high.

Summary:

This dangerous condition is easy to avoid.

• Ensure that you replace electrolytes as well as water.
• Drink enough to replace fluid lost through sweat and breath.
• Don’t overdrink.