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This is Your Brain. This is Your Brain on... Water?
Fact: Drinking is bad for you. Unknown fact: Drinking water is bad for you. Scary fact: Drinking water can kill you.
Research on runners in the Boston Marathon, published last Thursday in the New England Journal of Medicine and editorialized in the New York Times, has made a mockery of every athlete’s all-too-familiar “just keep hydrating” refrain. The research sounds another refrain: “All things in moderation.”
Too much hydration during intense exercise can cause hyponatremia, which is the condition of having too little sodium in the blood. Hyponatremia can kill you.
The basic breakdown of the condition is as follows: an abundance of liquid in your body dilutes your blood, reducing its sodium concentration and allowing water to enter your cells. The extra water expands your cells and they begin to push against your skull and brain stem. This process can cause seizures and a loss of vital functions, including the ability to breathe. People in this condition have fallen into comas, and those in the most severe cases have died.
You’re probably scoffing right now, as was I when I first read this study. I guess I sort of understand our national obsession with making carbohydrates evil, but give me a break here. Now water is bad for you? What’s next? Oxygen as a weapon for chemical warfare? And clearly, since we’re looking at marathon runners, there’s no need to scare people with this study, since this problem doesn’t affect the 99% of Americans who are not marathon runners. (Especially me. I belong on a bike.)
However, a closer look at the study’s conclusions made me think twice, especially the first sentence: “Hyponatremia occurs in a substantial fraction of non-elite marathon runners.” I certainly fall into that category. I’m about as non-elite as you can get. Even worse: according to the Times, this condition has also been found in individuals participating in long military maneuvers, in sustained hikes through the desert, and in extended bike rides. (Uh oh. I’m dead.)
Here are some details: the study was conducted on 488 runners in the 2002 Boston Marathon. After the race, participants provided a blood sample and detailed their fluid intake and urine output over the course of the race. Thirteen percent of participants (62 runners) had abnormally low levels of sodium in their blood, and three were in danger of dying.
One woman, exhausted after running for five hours while guzzling fluids all day, collapsed at the end of the race. Assuming she was dehydrated, she had chugged a 16-oz sports drink shortly before collapsing. She was pronounced brain-dead from a lethally low concentration of salt in her blood. Scary stuff.
Even more frightening for us middle-tier athletes is that it wasn’t the top runners in the marathon who had hyponatremia. Marathoners who finished the race in less than four hours were generally not at risk, but those who took longer, and therefore had more time to gulp fluids, experienced the condition. Participants who took more than four hours to finish the marathon drank an average of 13 cups of fluid over the course of the race, which is enough to cause them to gain weight during the race.
And contrary to popular opinion, sports drinks like Gatorade are mostly liquid, and the electrolytes they do contain do not effectively replace the sodium an athlete loses through sweat.
Worse, where coaches and friends are undoubtedly trying to be helpful, the false assumption that a sodium-deprived athlete is dehydrated can prove fatal if the person has more liquid administered to them.
The good news: hyponatremia is both preventable and treatable. In an article in last Thursday’s New York Times, Gina Kolata explained that runners can estimate what their water intake should be for a race such as the marathon. Weighing yourself before and after training runs will give you an idea of how much weight you lose, and therefore how much water you should replace while running. (Weight gain is a sign of hyponatremia.)
Other ways to reduce the risk include drinking while moving and refraining from chugging at the end of the race.
I’m not sure if I’ve decided where this theory ranks on the scale of crack-pot theories that describe the variety of exercise-related conditions that can kill you. The fact that some middle-of-the-pack runners have died from this condition makes the danger much more real. And I do know that eating salty foods while I bike makes me a better biker.
Although that may just be because I like pretzels.