Fluids crucial to man's survival

WASHINGTON: Nothing refreshes like an ice-cold drink on a hot summer day.

Fluids replenish the body's cooling system, enabling it to survive sweltering heat or elevated body temperature due to exercise. Sweating cools the body by evaporating water on the surface of the skin and dispersing excess heat.

Although deficiencies of other nutrients can be sustained for months or even years, a person can survive only a few days without fluids. Experts rank fluids second only to oxygen as essential for life.

In addition to offering true refreshments for the thirsty, fluids play a vital role in all bodily processes. They supply the universal medium, in which various chemical changes of the body occur, aiding in digestion, absorption, circulation, and lubrication of body joints.

Waste

For example, as a major component of blood, water helps deliver nutrients to body cells and remove waste to the kidneys for excretion. Secretions essential to digestion are also primarily water, working to break down food so that nutrients can be absorbed in the intestine.

Water comprises about 50 to 70 percent of body weight in humans. Males on average have a higher percentage of body water than females, because they tend to have less body fat. The more body fat in individuals, the less water therein. A decrease of as little as 10 percent of adult body water due to excessive vomiting or diarrhea is considered serious, and in a young child, could be fatal.

Average adults need about eight glasses of fluid each day for optimal health. Although experts generally advise drinking several glasses of water a day, the need for fluid can also be meet by consuming a variety of foods and beverages.

Milk is about 87 percent water; soft drinks about 90 percent; meat from 40 percent to 75 percent water; and vegetables as much as 95 percent water. Even foods considered "dry" such as cereal and bread contain about eight to 35 percent water.

Water supplies small amounts of a variety of minerals vital for life, such as sodium, potassium, calcium, copper and magnesium. Minerals, such as calcium, are essential to bone formation and blood clotting, while magnesium is needed to produce energy and conduct nerve impulses. Different concentrations of these minerals determine whether water is considered hard or soft.

Thirst signals the body's need for fluid. But some experts believe the thirst mechanism cannot be considered entirely reliable, and that slight dehydration has already occurred by the time a person becomes thirsty. For this reason, athletes and other active persons must be sure to consume adequate amounts of fluids for optimal performance.

"Drinking enough fluid is certainly key to maximum athletic performance," Nancy Clark, M.S., R.D., of Sports Medicine Brookline, one of the largest athletic injury clinics in the Boston area, said. "But it's even more basic than that. It can make the difference between feeling great or drained after exercise."

(Adapted from Food Insight with the permission of the International Food Information Council Foundation)