It was a very hot summer. A young man showed up to my ICU several years ago after suffering a seizure. His sodium level was dangerously low, which was the cause of his seizure. He was treated and recovered quickly. When he regained consciousness, I asked him his story.

He told me that he rode from Ohio to Illinois on his motorcycle. He had a helmet on, and it was very hot. He sweat profusely. Here’s the key: he drank only water the entire time.

This summer is also turning out to be very hot, especially in the Western United States. That means we will be sweating…and sweating a lot. When that happens, we not only lose water, but we also lose electrolytes (that’s what the white marks on our hats are). If we only replace water and not the electrolytes, we “dilute” the level of the electrolytes in our blood.

So for my patient above, he lost a lot of salt in his sweat, and he only replaced the water. By the time he reached me in the ICU, his sodium level was so dangerously low it caused him to suffer a seizure. Mind you, this only took a few hours to happen.

The same thing can occur during a competitive race, such as a marathon. When running for several hours and sweating, if only water is consumed, then the blood sodium level can also decrease to dangerously low levels and cause serious illness and even death.

That’s why we need to be very mindful this summer when rehydrating. If we will be out in the heat for hours and hours, we need to make absolutely certain we also consume foods with electrolytes, such as sodium and potassium.

Commercial hydration drinks have those electrolytes (albeit not very much). But so do foods like pretzels or even fruits and granola bars. Coconut water is also an excellent choice for rehydration. When I ran the Chicago Marathon in 2010, I made sure to drink Gatorade and not just water at each hydration station. And, thank God, I never cramped up.

I love summer: I love the warmth, the sun, the long days. There is so much fun to be had. With the summer fun comes the summer heat. We need to be very careful on how we rehydrate when out in the heat and sweating profusely. Sometimes, drinking just water can be very dangerous.