Water makes up nearly 85 percent of our brain, about 80 percent of our blood and about 70 percent of lean muscle. As our bodies are one-half to four-fifths water, then a lack of water - dehydration - could impact our health. If water is such a key component of our bodies, why is it so difficult to confirm how much water humans should consume to be healthy?  Reading the available literature would leave one a bit more than confused.

Some literature indicates that 75% of Americans are chronically dehydrated. Currently the recommendation for water consumption per day is eight, eight-ounce glasses per day popularly known as "8 x 8".  But this recommendation has been questioned by some in the medical community as excessive.  The American Physiological Society states, “Despite the physiological importance of water to life, little is known about water intake and excretion patterns in free-living individuals, because fluid intake, particularly from noncaloric, nonalcoholic, and noncaffeinated beverages is poorly documented.”

Some say since we get water from our food, we don’t actually need to drink eight ounces of water eight times a day.  They point out that we get some water from other drinks we consume even if they are caffeinated teas, coffees, or soft drinks.  As with anything that can be measured or prescribed, variables such as age, weight, geographic, social, and cultural variables also play a role in determining how much water consumption is  appropriate. The trouble is that so much of what we need is situational.  Moderation and common sense would say, when you’re thirsty, take a drink and drink what you need.  

What Does the Information About Dehydration Say?
Literature indicates that dehydration causes people to be less able to perform at their peak and its presence sets people up for weight gain, joint and muscle pain, fuzzy thinking, disease, and fatigue.  Dehydration can cause irritability, anxiety, depression, food cravings, and allergies.  Emergency thirst signals include feeling sick upon rising in the morning, heartburn, migraines, angina, joint pain, back pain, colitis pain, fibromyalgic pain, constipation, late-onset diabetes, and hypertension.

What about the elderly? Among people over 65, dehydration is one of the most frequent causes of hospitalization.  Also, as growth hormone production decreases in our early twenties, the thirst response also decreases. As we age and become less aware of being thirsty and drink less water, the water content within cells decreases so that cellular water can be redistributed to the brain and other vital functions.  But recommendations to increase fluid intake to eight 8-oz glasses of water in the elderly may need to be regulated due to a possible elevated risk of over hydration. Their body’s cells may not be effectively moving water through the system. Thus researchers suggest that fluid intake for the elderly be increased during periods of acute thermal stress.

Did You Know?

• The average person consumes about 16,000 gallons (60,600 liters) of water during his or her lifetime.
• In an average diet, solid foods provide an estimated three to four cups of water a day.
• 10 cups of fluid a day are lost through sweating, exhaling, urinating and bowel movements.
• Water accounts for about 60% of a man's body weight. It represents about 50% of a woman's weight.
• Dehydration is a major cause of infant illness and death throughout the world and hospitalization for the elderly.
• Water will be taken from blood volume during the first hours of water deprivation.
• It takes longer for nutrients to be delivered to and from muscles with dehydration.
• Athletic performance can drop by as much as 20 - 30% if you lose as little as 4% of your body's water during exercise.
• Water losses of 9-12% total body weight can be fatal.
• If you’re exercising or it’s hot, the body can lose two quarts per hour.
• Thirst can be blunted by exercise and overridden by the mind.

Are we drinking enough water?
Thirst isn't always a reliable gauge of the body's need for water, especially in children and older adults. Even slight dehydration can sap your energy and make you feel lethargic. A mere two percent drop in body water can trigger fuzzy short-term memory, trouble with basic math, and difficulty focusing on the computer screen or on a printed page. Even mild dehydration will slow down one's metabolism as much as 3%.  Athletic performance can drop by as much as 20 - 30% if you lose as little as four percent of your body's water during exercise. Lack of water triggers daytime fatigue in many people.

Some studies show that 70% of pre-school children drink no water at all during the day.  Some have a diminished thirst mechanism, and mistaken it for hunger, feeding their thirst with food.  In a UW experiment, one glass of water shut down midnight hunger pangs for almost 100% of the dieters. Dehydration is prevalent among people who drink caffeinated coffee, tea, and sodas. Americans consume about 21% of their calories from beverages.  Many adults especially those over 60 often drink only when thirsty and may get only 90% of what they need.  Preliminary research indicates that 8-10 glasses of water a day could significantly ease back and joint pain for up to 80% of sufferers.
Drinking five glasses of water daily is said to decrease the risk of colon cancer, breast cancer, and bladder cancer.

The Water in Your Body is a Hard Worker
Dehydrated cells shrivel; just imagine a prune instead of a plum. Most people don’t think of dehydration as a cause of pain, but this shriveled state of our cells can cause headaches and muscle and joint pain.  According to F. Batmanghelidj, MD of Global Health Solutions, Inc., “Water is a basic need for cellular health. Cells both contain and are surrounded by water. In dehydration, cell membranes become less permeable and accumulate toxins and acids which can lead to hampering the flow of hormones and nutrients into the cell and preventing waste products such as oxidants that cause cellular damage from flowing out.”

Water generates energy as it flows through a cell's membrane. Water is also necessary for the metabolic breakdown of ATP, another source of cellular energy. In addition, water acts as a bonding adhesive in the cell structure. The digestive system must have water to break down and digest food.  Red blood cells use it in collecting oxygen in the lungs.
 
Batmanghelidj adds that, “When a body becomes dehydrated, the neurotransmitter histamine is activated. Histamine, in turn, activates prostaglandins, kinins, and vasopressin, in an effort to redistribute available water according to priority. In addition to managing water during dehydration, these compounds cause other diverse effects. Prostaglandin E, for example, manages water regulation during dehydration and also inhibits the manufacture of insulin, thereby contributing to high blood sugar.”

Water also regulates your body temperature and by enabling waste removal it lessens the burden on your kidneys and liver as well as dissolving vitamins, minerals and other nutrients so your body can use them.  When we become dehydrated many will experience some type of pain caused by concentrated histamine, prostaglandins, and kinins.  

In addition to drinking plenty of water, adequate salt intake is needed for proper hydration. Salt, a natural anti-histamine, keeps water from being excreted and balances the intracellular and extracellular 'oceans' within us. Salt is also necessary for extracting excess acidity (in the form of hydrogen ions, oxidants from ATP production) from cells. In addition, salt is used by the body to balance blood sugar levels, to clear mucus and phlegm from the lungs, to aid absorption from the intestinal tract, to support nerve cell activity, and to strengthen bones. For every two quarts of water consumed per day consider an additional 1/2 teaspoon of salt added either to the water or food.

What are kids drinking? 
Are kids getting enough water in their diets?  Studies show that 70% of pre-school children drink no water at all during the day. A national survey conducted by Cornell Medical Center found that children that drank more than 12 fluid ounces of sweetened fruit juices a day are prone to obesity and reduced growth. An active, 50-pound child needs about a quart each day to stay hydrated. And during exercise, an additional five ounces of water is required every 30 minutes.

Sports drinks are heavily marketed to kids.  Sports drinks can be useful when consumed after or during vigorous and prolonged exercise in high heat. But most experts agree that water works better than carbohydrates or sugared beverages for moderate exercise. It’s best to expose children to water early in their development, before they acquire a taste for sweetened beverages.

Energy drinks are also hugely popular with youth and many contain high amounts of caffeine. Besides the caffeine dehydrating the body, they contain sugar and other chemicals and additives.  Young people are lured by promises of high energy, possible weight loss and greater sports endurance. Misuse and dependence on these drinks as a form of hydration or quick energy is an emerging health concern.  31 percent of U.S. teenagers say they drink them according to a recent AP survey. It’s no surprise this industry grew by 80 percent in 2006.  

Soft drinks, sodas, and caffeine containing coffee or tea, as well as alcohol containing drinks reduce the effectiveness of our water transfer systems in our body. Through reverse osmosis the body filters and injects water into cells which causes it to raise blood pressure to overcome the osmotic pull of water out of the cells. That's why high-blood pressure can be linked to dehydration.  Alcohol stops the process of reverse osmosis and reduces the effects of our cell’s filtering system.

The first sports drink, Gatorade, contains a lot of sodium (the endurance formula contains 200mg of sodium) and is six percent sugar, thus consuming too much of this or other sports drinks is not a good replacement for water. According to research by the Gatorade Sports Science Institute additional sodium in sports beverages may encourage drinking and aid rehydration after activity.  research revealed that small amounts of sodium added to a flavored, sweetened beverage increased drinking and improved fluid replacement following intense exercise. But what if sedentary kids are drinking such sports drinks while “working out” at their video games or drinking it several times during the day at lunch or for a snack after school when they haven’t had the commensurate workout Gatorade was developed for?

Like soft drinks, the so-called energy drinks like Red Bull "have huge amounts of caffeine -- which can be a diuretic and can even have a laxative effect," says Leslie Bonci, MPH, RD, director of Sports Nutrition at the University of Pittsburgh Medical Center. This can worsen the dehydration often experienced with heavy exercise.

Good Ideas to Increase Water Intake

• Carry a water bottle with you or in your car.
• Use a straw. Some people find it easier to drink more water this way.
• Drink at set times of the day; for instance before you drink your cup of coffee in the morning, or after you brush your teeth, or just before you eat or at break time.
• Substitute your customary soda or coffee for a drink of water instead.
• Drink at random times of the day. For example, take a drink every time the phone rings or every time you take a break.
• Set alarms on your watch or computer for every couple of hours to remind you to take a drink.
• Drink water steadily over the course of a day especially one full of exercise such as skiing or hiking. Don't rely solely on thirst to be your guide.
• Introduce children to water or diluted juice as a way to quench their thirst. Monitor consumption of juices, sports drinks and soft drinks.
• Discourage your children’s schools from carrying caffeinated or sugary drinks in school vending.

Sources:
You Are What You Drink
Just How Much Water Do We Really Need?
Gatorade Tough on Teeth?
Sports Drinks Go Way Beyond Gatorade
Visit Human Water Requirement Calculator to determine your daily water requirement.