Heat, Humidity and Hyponatremia
Runners have plenty of things to worry about, like bra burn, black toe nails and how much dental insurance you'll need if you try to chew a cold PowerBar.
But exercise physiologists and biochemistry specialists are now examining a serious condition called hyponatremia, or low blood sodium, which results from drinking too much water -- before and during lengthy periods of exercise -- instead of sports drinks containing adequate amounts of carbohydrates, and electrolytes, such as sodium and potassium. It's ironic, because we've always been told to drink gallons of water before, during and after exercising, and to keep a tight rein on our hydration management during endurance efforts.
Water is still a vital component for all athletic endeavors. But sweating out salt, and drinking too much water, which lacks electrolytes and carbohydrates, dilute mineral levels in the bloodstream and cause a menacing metabolic meltdown.
Sports drinks are designed to speed fluid absorption and are formulated to replace electrolytes lost through sweat, and replace sodium secreted during marathons and ultramarathons. But, not all sports drinks are created equal; always check the label of ingredients.
Research suggests that the optimal carbohydrate concentration of well-absorbed and tolerated sports drinks to be 4 to 8 percent. There also should be at least 75 to 100 milligrams of sodium for every eight ounces of fluid, because sodium helps maintain and restore the body's fluid and electrolyte balance. Carbohydrates and sodium are compatible partners which work together to increase water absorption in the intestinal wall. And, last but not least, you must like the taste of your sports drink, regardless of the brand.
This was all rattling around in my brain at last October's Marine Corps Marathon in Washington, D.C. The temperature was in the high 70s and sunny; the field of nearly 25,000 was filled with beginners, and charity walkers and runners, who took up to six hours to get to the finish line.
USA Track & Field gave the marathon their official sports drink to serve at aid stations. The drink lacks the proper carbohydrate concentration, and in my opinion, it also tastes like cough syrup. Water became the fluid replacement of choice -- a recipe for disaster.
The threat of hyponatremia has become so serious that technicians at major marathons like Boston and Pittsburgh are testing the blood of runners after the race to detect any abnormalities that indicate electrolyte levels gone haywire.
Extremely low sodium levels prevent the body from maintaining a normal fluid balance, and this has a very dangerous effect on the brain and lungs, which end up accumulating excess fluid: the brain swells and the lungs are flooded. In fact, hyponatremia is sometimes called "water intoxication."
Symptoms of hyponatremia, some of which mirror warnings of dehydration, heat stroke or heart attack, include nausea, vomiting, muscular weakness, shortness of breath, headache, lethargy, disorientation, confusion and seizures -- perhaps leading to coma or death. Sadly, it's suspected that runners actually suffering from hyponatremia in the past may have been fatally misdiagnosed with dehydration or cardiovascular incidents.
Hydrating with just water does not pose a hazard for runs lasting an hour or less. But runs or endurance feats lasting longer than one hour must be nourished with sports drinks that include electrolytes.
Women and novice marathoners tend to be at greater risk for hyponatremia. Physiologists suggest this might be true because women and rookies are much more methodical about hydrating days before an event, and often stop at every aid station for drinks during a race. And both groups tend to take longer to finish a marathon -- four to six hours, and therefore are likely to ingest more water.
If summer temperatures ever arrive, you can expect the 20K and half marathon races, trail ultras and marathon training to be quite a challenge. Don't just throw a pinch of salt over your shoulder and expect to be lucky. Here are some tips from the American Running Association and the Gatorade Exercise Physiology Laboratory to keep hyponatremia from making you the next post-race lab experiment.
Resist the temptation to drink more water than you sweat. Weigh yourself before and after long training runs to determine how much water you lose. Then drink enough to replace the weight loss.
Begin all workouts well-hydrated (at least two full cups), and drink five to 10 ounces of sports drinks every 15 minutes of exercise. Don't dilute the sports drinks with water because it negates the proper electrolyte formula that is established on the ingredient label.
Eat a moderately salty diet in the days leading up to the marathon. Check with your physician if you have health issues regarding sodium intake. Eat pretzels during the last half of an endurance training run or race. (Marine Corps gave bags of pretzels to all runners post-race.)
Encourage race directors to provide sports drinks and salty snacks at aid stations, or carry your own supplies.
Exercise scientists suggest the following fluid intake recommendations all year long:
Daily, drink three to four quarts or more, at least half of it calorie-free water. Avoid fluids with caffeine, alcohol, sugar and carbonation, which impede hydration.
Two hours before exercise, consume 16 to 20 ounces of water.
About 15 to 20 minutes before exercise, drink another 16 ounces.
Every 10 to 15 minutes during a run, ingest six to 12 ounces of water. To enhance consumption and absorption, the water should be about 40 to 50 degrees Fahrenheit.
How much fluid to take at each aid station is now defined by "gulps." Consider one big gulp one ounce of fluid.
After running, drink 16 ounces for each pound of body weight lost with sweating, and continue to drink throughout the day until your urine is a pale yellow or clear.
To learn more about fluid recommendations and sports medicine-based research, click on the Gatorade Sports Science Institute Web site at www.gssiweb.com; or the American College of Sports Medicine site at www.acsm.org.
-- Diane Sherrer
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