Thursday, March 4, 2010

How Much Water You Should Drink

How can you know how much water you should drink? Back in school we all memorized that we need 8 glasses of water per day. Let’s reconsider that. Are we all identical twins? Do we all have the same amount of muscle? The answer is NO! That might be a good general public health recommendation, but we are unique when it comes to fluid needs. For some of us, 8 glasses of water a day aren’t enough. For others that is far more than what they need.

Our bodies are 65% to 70% water. This percentage is lower if you have more body fat. Body fat has very little stored water, maybe less than 10%. Not so with muscle. Muscle can be 70% water. The typical American gains body fat and loses muscle throughout adulthood. However, this is not part of normal aging! Keep in mind that it is not “normal” to have that shift in body composition. I remind you that it can be prevented by a balanced exercise routine, one which includes strength training.

Functions of Water

What’s the function of water? Certainly if you’re thirsty it refreshes you, but what are its internal functions? It serves as a transport vehicle for digestion and a transport of nutrients to the cells within the blood. Maintaining an adequate blood volume enhances nutrient delivery, which makes us healthy and feel well.

Have you ever gone from a sitting to a standing position quickly? All of the sudden you get light-headed and dizzy. This is because you don’t have enough blood volume. You are not delivering enough carbohydrates to your central nervous system and your brain kind of goes into a holding mode. This is a great example of water serving as a transport vehicle.

Water also has mechanical functions. It lubricates joints. It makes up tears, which removes any dirt you may have in your eyes. For most of us, however, one of the most important functions of water is to regulate body temperature. Water is really good at holding and getting rid of heat.

How to Know How Much Water You Should Drink

How do we test our hydration level? How can you know, as an individual, whether or not you are well hydrated? A significant amount of fluid comes out in your urine, so your urine color can give you an idea of whether you’re hydrated or not. First morning urine is better. When you get up in the morning your urine should look like pale lemonade. If it looks like that you did a good enough job the day before. It shouldn’t look like water, but like pale lemonade. If you get up in the morning and it looks like apple juice, you didn’t do a great job. If you get motor oil, you probably need to get to the emergency room!

What about thirst as a measure of hydration? Can we trust thirst with how much water should you drink a day? There is a lag between the time you get dehydrated and the time you actually experience thirst. The old saying “if you’re thirsty you’re already dry” is probably true. Also, the older we get, the less sensitive this thirst mechanism is.

Hydration and Exercise

What should we drink when we exercise? If you exercise less than an hour, moderate intensity, water is just fine. The rules change if the activity is really intense or you’re exercising in the heat for an hour or more. In this case you probably need to switch to sport drinks. Sport drinks are intended to be used during physical activity, they’re not a lunchtime beverage. It is proven that when a beverage is flavored we tend to drink more of it. So, one advantage of sports drinks is that you get more fluid. The other valuable thing is the sodium you get from them.

If you’re outside exercising and you’re sweating, what does your sweat taste like? I know you had that experience. Sweat tastes salty. The major mineral that is being lost in sweat is sodium. Everybody talks about potassium and how good it is (which is true), but what you really need during exercise is sodium. The potassium losses in your sweat are really insignificant.

Sport drinks provide calories, fluids and the sodium that is being lost.

To go a step further in knowing how much fluid you need during exercise you can calculate your sweat rate. Your sweat rate is how many pounds you lose doing physical activities. For each pound you lose after physical activity, you lose 16 ounces of sweat. That’s significant. To rehydrate you need anything between 16 and 24 ounces of fluid. Why do we need that extra fluid? Why can’t I just replace those 16 ounces of sweat with 16 ounces of water? Some of that water would be lost in urine. What we are trying to do is to rehydrate the muscle.

So, find out how much water you should drink per day as an individual. The universal recommendation of 8 glasses per day keeps most people hydrated, however. So, if you’re not exercising in the heat, that might be a good amount to start. It is better for you to do your own experiments, though. Watch your urine!

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