Eight Glasses Of Water A Day: Myth Or Medicine?

The nutritionists tell us “You Are What You Eat.” Yet if one wants to be matter of fact, humans are mostly what they drink. So, how much of that should be water?

According to the National Institutes of Health, about 60 percent of the average adult human body is made of water. This includes most of our brain, heart, lungs, muscles, skin and about 30 percent of bones. As one of the main ingredients in the recipe of human life, water regulates our internal temperature, transports nutrients throughout the body, assists in flushing waste, forms saliva, lubricates joints and even serves as a protective shock absorber for vital organs, including our brain, and the ever important fluid protecting the unborn child in the mother’s womb.

Humans are constantly losing water from their bodies in exhaled breath, however, the primary loss occurs via sweat, urine and bowel movements. For proper body function, one must replenish the water supply by consuming beverages and foods that contain water.

There is no dispute that water is crucial for a healthy life or any life at all, for that matter. With this level of importance, unfortunately there remains little scientific consensus about the exact amount of water an individual should consume each day. So how much water do you actually need to drink to be healthy?

The National Academies of Science, Engineering and Medicine determined that an adequate daily fluid intake is about 15.5 cups (124 oz/3.7 liters) of fluids for men and 11.5 cups (92oz/2.7 liters) of fluids a day for women. These recommendations cover fluids from water, other beverages and food. About 20 percent of daily fluid intake usually comes from food and the remaining 80 percent from drinks.

What about the advice to drink eight glasses a day?

You have probably heard the advice to drink eight 8-ounce glasses of water a day. That is easy to remember, and it’s a reasonable goal.

Most healthy people can stay hydrated by drinking water and other fluids whenever they feel thirsty. For some people fewer than eight glasses a day might be enough. Yet, others may need more.

Factors that influence water needs:

Exercise: If you do activity that makes you sweat, you need to drink extra water to cover fluid loss. It’s important to drink water before, during and after a workout.

Environment: Hot and humid weather requires the body to cool via sweating and requires fluid replacement. Higher altitudes cause additional water loss as your respiratory rate increases to adapt to lower oxygen levels.

Overall Health: Your body loses fluids with fever, vomiting or diarrhea. Bladder infections, urinary tract stones and other medical issues may require additional fluid intake.

Beyond the tap, other sources of water can be provided by what we eat. Specifically, many fruits and vegetables, such as watermelon and spinach, are almost 100 percent water by weight. Additionally, beverages such as milk, juice and herbal teas are composed of mostly water. Even caffeinated drinks, such as coffee and soda, can contribute to your daily water intake. However, caffeine promotes diuresis — water loss via the kidney — and sodas with calorie heavy or artificial sweeteners present another set of concerns. Alcohol and highly caffeinated energy drinks can result in net fluid loss.

So, the recommendation for eight 8-ounces glasses of water per day is reasonable but not a hard fast rule. Your fluid intake is probably adequate if you rarely feel thirst, and your urine is colorless or light yellow. Yes, look at and be aware of your urine color.

Although uncommon, it’s possible to drink too much water. Yet the kidneys, which some say are smarter than most doctors, generally keep us in fluid and electrolyte balance.

Dr. C. Clark Milton is a fellow of the American College of Osteopathic Internists and the medical director of Corporate Health at Wheeling Hospital.


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