If you’re like me, you’ve probably heard that drinking 8 glasses of water a day of 8 ounces each is good for your health. I’ve even recommended this 8 x 8 strategy to patients.
But I’m rethinking it.
It’s hard to find any firm scientific data to show that drinking that much water improves your health. The original source of the 8 x 8 mantra is difficult to track down in the medical literature: at best it seems like a mis-interpretation of a 1945 US Food and Nutrition Report, repeated in a 2017 European Food and Safety Report, both of which actually made recommendations based on the total liquid content a person consumes in a day — including the water in fruits, vegetables, coffee, tea, etc. Not water alone.
Endurance athletes are in particular need of proper hydration. If you exercise extensively you need extra water. And if you’re outside on a hot day, your need for water is even greater. But athletes are also likely to be susceptible to the mythology of hydration.
It used to be believed that post-exercise muscle cramps were due to under-hydration. But it’s more likely that your muscles cramp if you’ve been drinking too much, not too little. More athletes get into serious trouble from over-drinking than from under-drinking.
The big issue with drinking too much is that all that water dilutes the electrolytes in your body. You can actually have too little sodium in your blood. That’s called hyponatremia. Then your nerves and muscles can’t fire properly.
Your kidneys are expert at controlling the levels of sodium and other electrolytes in your bloodstream. If there are too many dissolved minerals in your blood, the kidneys will create urine that’s more concentrated in order to even the score. Too few electrolytes? The kidneys will pass more diluted urine to get rid of the extra water. You don’t necessarily need to override this process by drinking water based on a formula.