Thirsting for Hydration Tips

It might happen at a high school cross-country meet. It might happen during an Ironman competition. It might happen in the upcoming Olympics in Rio. It might happen to a hiker in the Grand Canyon, celebrating the 100^th anniversary of the National Park System.  In all of these scenarios, an athlete, having endured a long, hot, grueling period of exercise, finally reaches the finish line and collapses.  If it is a sponsored event, the medical team rushes to assist the athlete. What causes an athlete to collapse during or after exercise?  How does hydration factor into a collapse?

The most serious cause of an athlete collapsing is sudden cardiac arrest.  In athletes over the age of 35, the most common cause of sudden cardiac arrest is a heart attack (lack of blood flow to the heart muscle).  In younger athletes, sudden cardiac arrest may be caused by a thickened heart muscle, a weak heart muscle, a heart artery that follows the wrong course or an irregular heart rhythm.  Sudden cardiac arrest must be diagnosed and treated immediately (including defibrillating the heart back to normal rhythm) if the athlete is to survive.

Another cause of collapse is exertional heat stroke. This is a true medical emergency and is called a “heat attack”.  Heat stroke occurs due to the combination of a hot outside temperature plus extensive heat production by the body during exertion.  It is usually preceded by heat exhaustion characterized by dizziness, headache, and confusion. With heat stroke, the patient is disoriented and is not sweating. If untreated it progresses to coma and death.  Heat stroke is diagnosed by a body temperature of 104 degrees or greater.  The key finding is a victim with a high fever, but cool dry skin; the body’s mechanism for getting rid of heat (sweating) has been turned off. The treatment is immediate cooling by moving the patient into the shade, and applying cold compresses to the chest, head, neck and groin. Heat stroke may be prevented by taking precautions in hot weather and avoiding dehydration.

On the other end of the spectrum from dehydration is water intoxication or too much fluid in the body. This condition is also called exercise-associated hyponatremia  (low sodium content of the blood).  As we go through our day, and even more so when we exercise, we lose water by sweating, when we breathe, in the gastro-intestinal tract and of course when we urinate.  When we lose enough water, our body tells us we are thirsty and we drink to replenish the lost fluids.  The amount of fluid in the body is very tightly regulated.  If we are dehydrated, a hormone is released (arginine vasopressin) which tells the kidneys to hold onto more fluid and it stimulates the brain’s thirst mechanism to make us drink.  Water intoxication occurs when fluid intake (water, sports drinks or other fluids) far exceeds the loss of fluid through sweat, respiration and urination.  More and more fluid builds up over time, so that we are “drowning in water”.

Water intoxication after exercise is a rare but life threatening condition. It can present with mild symptoms (lightheadedness, nausea) but more often presents with more severe symptoms such as headache, vomiting, and as swelling builds up in the brain, confusion, seizures and death.  At least 14 athletes have died from water intoxication since 1981. Water intoxication occurred in 16% of Grand Canyon hikers who sought medical care in a five-year period. The activities usually associated with it include endurance competitions (marathons, triathlons), hiking, military exercises and police training.  The main risk factor is sustained excessive fluid intake, over and above fluid losses.  It usually occurs in smaller individuals, exercise duration over 4 hours, less experienced exercisers, over weight or under weight, slow running pace and readily available fluids (for example, running a marathon at a slow pace and stopping and drinking at every station).

Exercise associated water intoxication is a life threatening condition and immediate diagnosis and treatment are imperative. Testing the sodium level in the blood makes the diagnosis.  The normal sodium level is 135 and severe water intoxication typically occurs with sodium levels less than 125.  The treatment is intravenous infusion of a fluid with a very high sodium concentration.

Exercise associated water intoxication may be prevented by following the mantra: Drink to Thirst. The best way to hydrate is to drink fluids before, during and after exercise when thirsty. The thirst response is more than enough to prevent dehydration and reduces the risk of water intoxication.

There are several misconceptions regarding thirst and hydration. One is the recommendation that athletes start drinking fluid before they are thirsty, erroneously believing that thirst is a poor guide to fluid replacement.  Another is that large amounts of water or sports drinks are needed to prevent exercise related muscle cramps.  More recent data points to neurological changes due to fatigue as the cause for muscle cramps rather than dehydration or electrolyte imbalance.  Another misconception is that dehydration is bad.  While dehydration is uncomfortable, causing headache and fatigue, it also adversely affects concentration, reaction time, memory, and reasoning. In elderly patients and those on certain medications, dehydration can cause low blood pressure, passing out and can result in hospitalization. However, moderate dehydration in athletes or otherwise healthy individuals is well tolerated and not life threatening. Therefore excessive drinking to prevent dehydration is not necessary.  Another misconception is that sports drinks, with added electrolytes, are better for hydration for athletes.  While sports drinks contain more sodium than water, their sodium content is still less than the sodium content of the blood. So excessive drinking of sports drinks can still result in water intoxication.  Using salt tablets may be helpful, but will be of no benefit if excessive fluids are still being consumed.  Lastly, there is no data to suggest drinking 6 to 8 glasses of water per day. In fact there are no formal guidelines on how much to drink each day. The amount of water for each person is affected by activity, body weight and the weather.

It is established that you must drink to thirst, but what should you drink to stay hydrated?  To answer this question, researchers tested several beverages against water. They assessed how much fluid from each beverage was still present in the body after two hours. There were several drinks, whole milk, fat free milk and orange juice, that provided better hydration than water, presumably because they emptied more slowly from the stomach. Surprisingly, drinks with caffeine, alcohol and sugar hydrated just as well as water, contrary to conventional wisdom. In addition, a sports drink also provided the same hydration value as water. It seems that the type of drink is less important for maintaining hydration than consuming an adequate volume of fluid.           

So, to avoid having the medical team rush in to help after exercising or to avoid being airlifted out of the Grand Canyon, a few things can be done. See your doctor to assess your risk for heart problems and sudden cardiac arrest before starting an exercise program.  Otherwise, each person should determine their own hydration needs, especially during exercise, and develop a strategy that accounts for the type of exercise, the environment and fluid losses.  In addition, listen to your body and drink when thirsty.