A Few Facts About Hydration
Water and the Body: A Job Description
• Transports nutrients and oxygen to cells
Research Council (NRC) uses a sliding scale of 1 milliliter
of water for every calorie burned. The NRC says the average
man — who burns about 2,900 calories daily — needs 2,900
milliliters, or about 12 cups, of water each day. The
average woman — who burns 2,200 calories daily — needs about
2,200 milliliters, or about 9 cups, of water each day. For
your own calculations: One measuring cup (8 ounces) of water
equals 236 milliliters of water.
• The American College of Sports Medicine (ACSM) recommends drinking about 17 ounces of liquid 2 hours before exercise and drinking early and at regular intervals during exercise (5-8 oz every 15-20 minutes).
• Mild to severe dehydration commonly occurs among athletes, even when fluid is readily available. Consequently, it is in the athlete’s best interest to adopt fluid-replacement practices that promote fluid intake in proportion to sweat loss.
• Vigorous exercise may delay the thirst mechanism, making it difficult to replace fluid loss without a plan for periodic consumption. Athletes should become accustomed to consuming fluid at regular intervals (with or without thirst) during training sessions so that they do not experience discomfort during competition.
• Increasing dehydration, due to inadequate fluid consumption, directly impairs stroke volume, cardiac output, and skin blood flow, which results in larger increases in body core temperature, heart rate, and ratings of the difficulty of exercise.
Hyponatremia (low blood sodium levels) as a
result of over-hydration, has become more and more common in
endurance athletes, and many governing bodies are changing
their hydration recommendations accordingly. To prevent
complications, endurance athletes are advised to be aware of
the effect of dehydration as well as over-hydration and plan
their fluid intake according to their individual needs.
• The average American is chronically dehydrated and consumes only 4.6 servings of water per day.
LOTS OF water and keep yourself on schedule” is an old
health adage. Recent studies have demonstrated that
drinking water is, indeed, associated with a substantial
physiological response. Drinking 500 ml of water increased
metabolic rate by 30%. The increase occurred within 10 min
and reached a maximum after 30–40 min. The total thermogenic
response was about 100 kJ (which equals about 96 kcal per
day or a loss of 5.5 lbs per year).
• Dehydration is one of the ten most common causes for hospitalization among Medicare patients. In 1991, 6.7% (731,695) of Medicare hospitalizations had dehydration listed as a principal diagnosis, costing Medicare more than $446 million in hospital payments. Most importantly, the study revealed that about half of the people over age 65 who were hospitalized with illnesses accompanied by dehydration die within one year of admission.
• Nursing facility residents are particularly at risk for dehydration. As many as 75% of residents have average fluid intakes below 1,500 cc per day, while a minimum recommendation is between 1,500 to 2,000 cc of fluid a day. These residents may need more opportunities and reminders to drink.
J Am Diet Assoc 1999 Feb;99(2):200-6.