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Don't Let Dehydration
Dampen Your Workout

Excerpt By Christine Haran, Healthology

Federal governments and health professionals are encouraging people to exercise more in order to combat obesity and to prevent chronic health conditions. But both experienced athletes and beginning exercisers need to be careful about exercising in hot weather conditions.

Even though sweating profusely may make you feel like your workout is in full swing, severe dehydration can be dangerous because the body can't function without a certain amount of water and electrolytes, which are minerals such as sodium that are lost in sweat and urine.

People need to apply common sense in order to stay hydrated during or after exercise, and serious athletes should take extra precautions. Below, Michael Sawka, chief of Thermal and Mountain Medicine at the U.S. Army Research Institute of Environmental Medicine in Natick, Mass., discusses the effects of dehydration and how it is best avoided.

How do you know you are dehydrated?
People generally refer to dehydration as a reduction in body water below normal levels. The first thing you'll probably experience is thirst. There is not a real precise relationship to how thirsty you feel and how dehydrated you are. Usually when you get the sensation of thirst, you're already somewhat dehydrated. You may get a headache. You may feel dryness of the mouth. If you are exercising or changing posture, you could feel dizzy. If you are in hot weather or exercising in the heat, you may feel hotter. Your skin may feel warmer. You would be urinating less frequently and smaller volumes, so your urine would be dark in color because it would be more concentrated.

There is also some evidence that both your physical and mental performance capabilities decrease as a result of dehydration. You may not be as sharp in terms of some of the types of complex cognitive functions that you have to do. So there are a variety of symptoms.

How can dehydration affect one's health?
Acute dehydration will increase your risk of heat exhaustion and heat stroke. [Heat exhaustion causes heavy sweating, fainting and vomiting, and heat stroke occurs when the body temperature rises to 106ºF or above.] Although it is not as well studied, there is evidence that shows that chronic dehydration can have a variety of different affects on chronic diseases, including urinary tract infections, and kidney stones and gallstones. Some evidence indicates that dehydration may be related to susceptibility to bladder and colon cancer. But that evidence is not real strong.

What are common causes of dehydration?
Many types of stress will cause under-drinking and lead to dehydration. Heat exposure and exercise are common causes. When you exercise, a normal response is to sweat to regulate your body temperature. You lose body water because you sweat more. And if you're exercising in hot weather, you have a greater requirement for sweating because you depend more on evaporation of sweat for body cooling. As a result, people can become dehydrated from physical exercise, particularly physical exercise in the heat.

People can become dehydrated in other ways as well. One other way is through medications. For example, blood pressure drugs such as diuretics are dehydrating because they work by decreasing your total body water.

It's also common to see dehydration as a result of diarrhea and vomiting.

How much water does one need in a day?
How much water you need in a day varies. It depends on a lot of factors: age, activity level, the environment you're exposed to.

For a normal healthy person, generally within reason, short-term under-consumption is not too much of a problem, unless you're physically active, because your kidneys will act to reduce your urine output to conserve water. Likewise, you don't have to worry about taking in too much fluid because your kidneys will remove what you don't need. Over-consumption can become a problem, however, during prolonged exercise (several hours) because urine output is reduced.

For healthy adults, if you're expending about 3,000 calories a day, the minimal amount you should take in would be about three quarts of water a day, roughly three liters. It doesn't matter if the water is contained in food or beverages.

For a very active person in very hot weather, such as an agricultural worker or maybe a soldier out in the field in hot weather, the requirements could be substantially higher. The government is going to be putting out some guidelines about this later in the year.

Who is particularly at risk for dehydration?
There is some evidence that children may be more susceptible to dehydration and that the adverse consequences may be more marked. The elderly and people who are sick are at risk because of their health. The elderly tend to under-drink anyway.

The physically active populations are also at risk. When you dehydrate, the thermal and cardiovascular benefits you get from adjusting to a high temperature, and high physical fitness, are greatly compromised. So these very fit people who go out and run hard, but decide they're not going to drink for whatever reason, lose these advantages during exercise.

At what point do electrolytes need to be replaced?
It depends. If you have diarrhea or vomiting, you can lose an awful lot of mineral electrolytes, so you should replace them right away. If you're performing exercise in temperate conditions for less than two hours, it may not matter. But if you're exercising in the heat, you probably want to start replacing electrolytes relatively soon.

The general rule of thumb is if you're exercising and having high sweat rates for any prolonged period — let's say over an hour — you probably then want to replace the electrolytes at a rate proportionate to what you're losing. Sports drinks contain electrolytes in concentrations proportionate to what is lost in sweat by a moderately trained athlete.

Should people replace electrolytes with a sports drink?
The National Academy of Sciences has looked at sports drinks, and they have their place. I think that it's fair to say that sometimes they're better than water and sometimes they're not. When you are doing high intensity exercise of a prolonged nature, the carbohydrates and the electrolytes sports drinks have can provide advantages. Because they contain sodium, they stimulate thirst and make it easier to hold the water that you ingest, and they provide the energy that's needed to sustain physical exercise. Athletes participating in hot weather training should consider their use.

But for the average person maybe just going out and playing a game of tennis or something like that, replacing carbohydrates and electrolytes is probably not a concern.

How can you monitor your hydration status?
One ways to check hydration is by monitoring your body weight. Generally, if you take your body weight every morning, it is relatively constant. If you take your body weight and it's down all of a sudden a lot one morning, you're probably dehydrated.

Another thing that you can do is monitor your urinary habits. If you're urinating more frequently than usual, and if it's relatively clear, you're probably very well hydrated. If you're urinating infrequently and it's dark, you're probably dehydrated. But there is no precise relationship between urine color and dehydration.

How can people who exercise avoid dehydration?
First of all, you should drink a nice tall glass of fluid maybe an hour before you exercise. If you're still thirsty have another one so that you have some idea that you're starting out hydrated. You want to stay away from carbonated beverages and those with high fructose because they can give people GI problems.

But overall, once you're post-exercise, drink whatever you want. If it's liquid, it's probably pretty good. An important point is that most people fully rehydrate their bodies at mealtime. So if you're concerned about hydration, one of the worst things you can do is skip meals. It's important that you have standardized meals in a comfortable environment with plenty of fluids available.

Should you avoid caffeine before exercise?
Not if you're a regular caffeine drinker. Coffee makes you urinate more, but the overall effects are not that significant in normal coffee drinkers. I wouldn't prehydrate on black coffee, but if you want to have some coffee it's not a big deal.

Is dehydration associated with heat stroke and heat exhaustion?
One of the things that you often see with dehydration is elevated body temperature. If a person is exercising in the heat, this causes greater than normal elevation in the body temperature, and cardiovascular strain.

Many years ago, when people didn't pay as much attention to replacing fluid, dehydration was very often associated with heat exhaustion and even heat stroke. However, now we pay a lot better attention to replacing fluids and dehydration, so the risk of these conditions is lower. However, modest dehydration — a loss of 2 percent of your body weight — can significantly reduce your ability to work out in hot weather.

What would your advice be in terms of avoiding exercise on hot days?
You can exercise on hot days. You don't want to overdo it like anything else. Clearly you should try to exercise in the cool of the morning or the evening hours. But if you're like most people, you exercise when you can.

If you're going to exercise in heat, use moderation. If you're sick or have health problems, you may want to not exercise or use caution. Don't go out on the hottest day and push it. Instead, scale back your activity levels. For example, you can walk instead of run, or run slower or for a shorter period of time. You can be active, but you have to gauge how much you do depending on the exposure and the amount of strain on the body. Use common sense.

Reference Source 104


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