BehindTheMedspeak: If you're a marathon runner, drinking too much water can kill you

Wait a minute — aren't runners supposed to drink water constantly, even when they're not thirsty?

What about the old saw, "Drink ahead of your thirst — if you're thirsty, it's too late."

That's all hogwash, is all that.

Today's New England Journal of Medicine features an article entitled "Hyponatremia Among Runners in the Boston Marathon."

The authors studied 488 runners who finished the race.

They took blood samples at the finish line and analyzed them: the surprising result was that fully 13% of the samples showed hyponatremia (low blood sodium), which can lead to "race-related death and life-threatening illness among runners."

0.6% (6 runners) had critical hyponatremia, three with levels so low they were in danger of dying.

Who's at highest risk?

Men who run slowly (over four hours for a marathon).

That gives them plenty of time to stop at every aid station and drink, drink, drink.

Dr. Tim Noakes, a hyponatremia expert at the University of Cape Town, said in Gina Kolata's article in today's New York Times about the findings, "Everybody becomes dehydrated when they race. But I have not found one death in an athlete from dehydration in a competitive race in the whole history of running. Not one. Not even a case of illness."

On the other hand, he said, he knew of people who had died from drinking too much water.

He said doctors and emergency workers at races sometimes assume sick runners are suffering from dehydration and give I.V. fluids, killing the patient.

The problem surfaced at the 2002 Boston Marathon, when a 28-year-old woman reached Heartbreak Hill, at Mile 20, after five hours of running and drinking.

Feeling terrible and thinking she was dehydrated, she chugged 16 ounces of liquid.

She collapsed within minutes and was later declared brain dead.

Her blood sodium was 113 mmol/liter (normal is 135).

As blood sodium decreases the brain swells, which can cause confusion, grogginess, and lead to seizures and cardiac arrest.

On a related subject: if you're planning on running a marathon but don't want to destroy your body training for and doing it, the best investment of money and time you can make is to buy and read Jeff Galloway's superb book, "Marathon: You Can Do It!" (pictured above).

It costs $11.17 at amazon.

After having run a number of marathons and half-marathons the old way, I tried Jeff's way — which includes short breaks for walking on a regular schedule.

Not only was my overall time lower but I actually enjoyed most of the race and felt fine afterwards as opposed to my usual weeks-long period of post-race pain and fatigue.

It's a great book for those of us who'll never break three hours – much less four — in the marathon.

Why should you believe Galloway?

Maybe because he's a former world-class runner and member of the U.S. Olympic team who has run over 130 marathons?

I dunno, seems like he might have useful advice to offer most anyone.