Kelly Hall, 34, was in fantastic shape, routinely biking 100 to 200 miles a week in preparation for last year’s AIDS Ride from Boston to New York. Usually, she trained with other riders, who made it a point to take food and hydration breaks. But one day last June, Hall, a strategic planner at Partners Community Health Care in Needham, decided to ride alone, despite the 95 degree heat.
The first 50 miles, around Concord, were a breeze. “I thought I’d do another 25,” she recalls. She drank a little Gatorade, the sports drink designed to restore normal blood levels of electrolytes, but relied mostly on water, constantly sipping from the 70-ounce Camelbak water supply on her back.
Halfway through the last loop, hyponatremia, a relatively rare but potentially fatal condition in which blood levels of sodium sink dangerously low, “hit like a ton of bricks,” says Hall. She finished her ride “really, really slowly,” got back to her car, threw up, drove home and threw up again. She made it to Brigham and Women’s Hospital, where she had a grand mal seizure.
Nearly the same thing happened to Sarah Snyder, 45, a Globe editor, who was training with friends for another long, benefit ride. She, too, was in good condition, and she too, dutifully sipped water for 56 miles. “What a good doobie I’m being,” she remembers thinking.
But after her ride, she threw up violently and was rushed to the hospital, where she drifted in and out of consciousness for 18 hours. “You drank too much water. You screwed up your sodium,” the doctors told her. When asked to say her name, “It came out like Swahili.”
Full-blown cases of hyponatremia (sometimes called water intoxication) are relatively rare, roughly 0.1 to 4 percent of people who sweat steadily for hours in grueling, long distance events, says Scott Montain, a research physiologist at the US Army Research Institute of Environmental Medicine in Natick. The incidence of hyponatremia appears to be highest in events lasting more than four hours, especially at high temperatures.
But the prevalence of warning symptoms is much higher – up to 27 percent of athletes who seek attention in a medical tent during a long race – and appears to be rising.
In the 1996 New Zealand Ironman Triathlon (3.8 kilometer swim, 180 kilometer bike and 42 kilometer run), researchers found that 9 percent of athletes who showed abnormalities on medical tests had hyponatremia.
Typically, conscientious athletes get in trouble because they adhere too diligently to one recommendation (drink lots of fluids) but ignore another (keep electrolytes up). (Electrolytes are charged particles such as sodium, potassium, calcium and bicarbonate that must be kept in near-perfect balance) Indeed, for most marathoners, Montain notes, the real problem is drinking too much water, not failing to take in enough sodium.
Women in particular, may be at risk, some researchers believe, in part because they may too dutiful about drinking water.
Some studies suggest that certain drugs may also increase risk, among them ibuprofen and other NSAIDS (non-steroidal anti-inflammatory medications), acetaminophen, some cancer drugs, nicotine, diuretics, narcotics and some antidepressants and anti-psychotic drugs. On the other hand, data presented recently at the American College of Sports Medicine meeting suggest that ibuprofen and other NSAIDS may not increase risk after all.
“When you sweat, you lose both water and salt,” says Dr. Soheyla Gharib, medical director of the women’s health center at Brigham and Women’s Hospital. “If you replace only water, the salt level in the blood gets diluted.”
And that can be disastrous. Normally, the body tries to keep positively and negatively charged electrolytes in balance to keep cells electrically neutral, says Dr. Ronenn Roubenoff, associate professor of medicine and nutrition and director of human studies at the Jean Mayer USDA Human Nutrition Research Center at Tufts University. Though sodium is probably the most important electrolyte for endurance athletes to worry about, he says, “an imbalance of any one of the electrolytes can be harmful.”
Normally, sodium is plentiful in the blood and relative low inside cells. But when the concentration in the blood gets too low compared to the amount inside cells – either because a person drank too much water, took in too little sodium, or both – water rushes into cells. “Water follows sodium as day follows night,” Roubenoff says.
The result is dangerous swelling, particularly in the brain, that can lead to brain damage, coma and death.
Curiously, hyponatremia can occur whether a person is dehydrated, normally hydrated or overhydrated because any of those conditions can happen while blood levels of sodium are too low, adds Roubenoff.
Further complicating things is that the symptoms of hyponatremia can be easily confused with those of heat stroke and heat exhaustion. With heat exhaustion (also called exertional heat injury), people feel ill, get nauseous, have muscle cramps and may feel dizzy standing up quickly.
With heat stroke, people have all those symptoms plus another one: mental status changes, that is, confusion about who and where they are and what day it is. People with genuine heat stroke also typically have extremely high body temperatures
With hyponatremia, people also feel very ill and may have mental status changes, but don’t have the high temperatures of heat stroke. They also vomit forcefully and repeatedly and, unlike those with heat exhaustion, do not feel better by resting and cooling off.
Treatment of hyponatremia may involve restricting fluid intake and promoting urine production, but some people also need intravenous (IV) salt water (saline) with a high concentration of salt, until blood electrolytes return to normal. Re-setting the water-salt balance “must be done carefully and slowly,” cautions Dr. Gabriel Danovitch, professor of medicine at the University of California , Los Angeles, School of Medicine because overly-rapid correction of electrolyte imbalance can cause further problems.
To protect yourself against hyponatremia, start by paying attention to how much you sweat. In general, women sweat less than men and their ability to regulate core body temperature (and sweating) may also vary with different phases of the menstrual cycle.
Individuals also vary considerably in how much sodium they lose in sweat. You may be a heavy sodium loser if your sweat burns your eyes, tastes salty or leaves a cakey-white residue on your skin.
Sweat contains between 1 to 2 grams of sodium per liter – and since it’s easy to lose a liter of perspiration in a long race, that means you’re losing this much sodium, too. You can replace 2 grams of sodium with about a half-teaspoon of salt.
You can also make sure you’re getting enough sodium by drinking sports drinks like Accelerade, Cytomax, Gpush, Gatorade and the like instead of plain water during long events. (Check the labels for sodium content; some brands have twice the sodium of others.) Sports drinks also typically contain carbohydrates as well, which provides energy and helps with water and sodium absorption.). These sports drinks are similar to Pedialyte and other oral rehydration solutions used to treat children who become dangerously dehydrated.
If you don’t like sports drinks, you could take salt tablets, but they may make you nauseous. At the very least, you can eat salty foods prior to and during a big event.
You can gauge how much fluid you’re losing by weighing yourself before and after half an hour of exercise. (Don’t drink anything between weigh-ins.) If you lose a pound in half an hour, your sweat rate is two pounds per hour, which means you need to replace that much fluid. (Two pounds of fluid is 32 ounces.)
As a practical matter, you’re probably not in any danger from dehydration unless you lose more than 2 to 3 percent of your body weight during exercise, but you can’t rely on thirst to guide you because by the time you’re thirsty, you may already be dehydrated. So the goal is to adjust your fluid intake to how much you sweat.
In fact, for ordinary mortals who work out for less than an hour, sports drinks are unnecessary and plain old water (along with the salt you normally get in food) will do just fine, says Roger Fielding, an exercise physiologist and associate professor of health sciences at Boston University.
For endurance athletes doing events longer than an hour and sweating profusely, it’s probably wise to drink 6 to 8 ounces of fluid every 20 minutes to prevent both excessive dehydration and hyponatremia, says Montain of the US Army lab. For events lasting longer than two hours, you’re probably better off with a carbohydrate-electrolyte sports drink than plain water. But don’t drink more than 40 ounces (1 and