Why Water?
Water is arguably the most essential nutrient for any active individual. This remarkable substance plays an important role in every major organ and system, and some two-thirds of your total body weight is water. Years of hydration research suggests that you should prevent even mild levels of dehydration. Relatively small sweat losses can hinder performance in hot weather and even in cool weather when you may be less aware of fluid losses. To prevent any adverse performance effects, you should begin all workouts optimally hydrated, which means staying on top of your daily fluid intake.
Besides being the major component in sweat, water plays many essential roles in your overall health. About two thirds of your body’s water is stored inside cells, giving them their shape and form, and well hydrated muscles are about 70-75 percent water. The rest of the water in your body surrounds these cells and flows within your blood vessels. Water provides structure to body parts (even seemingly solid bones), protects important tissue such as your brain and spinal cord, and lubricates your joints. Water also aids digestion through saliva and stomach secretions, and eliminates waste products through urine and sweat. Water is also essential for the proper functioning of all of your senses, particularly hearing and sight.
Daily Dose
In 2004, the Food and Nutrition Board of the Institute of Medicine released Dietary Reference intakes (DRIs) for water and various electrolytes. Reflecting the large variation in water needs among individuals, an adequate intake of 16 cups (130 ounces) for men and 12 cups (95 ounces) for women was recommended. This reflects your total fluid needs for the day, including sweat losses, which can vary greatly from exerciser to exerciser. How much fluid you need to consume to meet your daily fluid needs depends on your sweat losses and how much of a fluid deficit you have after workouts.
Don’t rely on fluid alone to gauge your fluid intake. Make a conscious effort to drink every one to two hours. When you are well-hydrated, your urine is pale, like the color of lemonade. Darker-colored urine (like the color of apple juice) or a smaller volume of urine indicates that you need to step up your fluid intake. Urine tends to be more concentrated when you wake up in the morning, but is should become clearer throughout the day. You should urinate at least four full bladders worth of fluid every day. Some vitamin supplements can darken or even lend a neon glow to the color of your urine; at these times, volume may be a better indicator of your hydration level. To test how you are doing on daily hydration, check your weight in the morning. Significant decreases in weight from day to day can be an indicator of chronic dehydration.
Dehydration
Fluid balance is simply the result of your intake of fluids versus your output of fluids. If your output of fluids is greater than your intake of fluids you may become dehydrated. When you are dehydrated, both your cells and blood decrease in water content and volume. According to the Mayo Clinic and other leading health care organizations, even mild dehydration can lead to health problems such as lethargy and constipation. Dehydration symptoms can include loss of appetite, minor headaches, dizziness and general lack of mental clarity. There is also evidence that drinking adequate water may help prevent some diseases, such as kidney stones, and may be associated with a lower incidence of colon cancer. At rest, urine output represents your greatest fluid loss. Fluid is also lost in the air that you exhale, which increases when you live in a dry climate or at altitude, or when exposed to warm or humid weather.
During your school or work day, aim for a scheduled fluid intake of 8 ounces every hour. In the two to three hours before exercise, consume one ounce of fluid for every 10 pounds of body weight. You can also top off fluid stores in the hour before exercise by consuming 8 ounces or more. After exercise, consume 20 ounces of fluid for every pound of weight lost during exercise
Hyponatremia
Although dehydration is far more common, it is possible to over-hydrate. Hyponatremia is a potentially deadly condition in which dangerously low blood sodium levels develop during or after prolonged exercise due to a combination of fluid overload and sodium sweat losses. It is most commonly seen during exercise sessions lasting longer than four hours (such as a marathon) and signs include rapid weight gain after exercise, bloated stomach. Swollen hands and feet, throbbing headache, dizziness, lack of coordination, and nausea and vomiting.
Experts agree that overzealous drinking prior to prolonged exercise, and fluid intake in excess of sweat losses during exercise, increases the risk of developing hyponatremia.
How does one prevent hyponatremia? By drinking to minimize or replace sweat losses without overdrinking, and by choosing a sodium-containing sports drink for prolonged exercise sessions. For a quick hydration check, weigh in before and after exercise. If you are down one pound or so, you are somewhat dehydrated. If you are gaining weight with your hydration efforts, you are likely over-hydrating.
RESOURCES
- Ryan, Monique. Fluids in your daily life. ACE Fitness Matters. July/Aug. 2007; Vol.13,(4): 5-6.
- American Council on Exercise (ACE) Fit Fact. Healthy Hydration, 2001.