Hyponatremia

As runners it’s crucial to understand not only how much water we need, but how much

Words Laura Hilton

Start talking to runners about fluid intake and most of us will be able to chat at least a little about the importance of drinking enough to stay hydrated, but in general, runners are much less informed about the risks associated with taking on too much fluid during a run. It’s defintely worth being aware of a condition called hyponatremia because, although rare, it can have life-threatening consequences.

What is it? First of all, it’s important to clarify that hyponatremia is not the opposite of dehydration. Instead, it’s a condition that occurs when the sodium level in the blood falls below the normal range of 135-145 milliequivalent per litre (mEq/l).

Sodium is one of the three main electrolytes (along with potassium and chloride) and it’s vital for fluid balance, blood pressure regulation as well as for keeping the nerves and muscles functioning optimally. We get it from food and drink in the form of salt and we lose it when we sweat. If we lose more than we take on, our sodium levels can fall dangerously low – and this is the point at which point we’re in danger of developing hyponatremia.

If the sodium levels in your blood get too low, this causes extra water to go into the cells of your body, making them swell. This can be incredibly dangerous in the brain because it swells against the skull until it reaches capacity. When there is no room left in which to expand, a person can go into a coma or even die as a result of hyponatremia.

Ultrarunner Sophie Power had an incredibly frightening experience with hyponatremia while racing in Drinking too much water can strip your body of vital sodium and cause the brain to swell Cambodia at the end of 2012. She was taking part in an event that covered 250K over six days in the hot and humid Cambodian jungle.