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How many glasses of water should humans drink every day?

Water is essential to good health, yet needs vary by individual. These guidelines can help ensure you drink enough fluids.

How much water should you drink each day? It's a simple question with no easy answers. Studies have produced varying recommendations over the years, but in truth, your water needs depend on many factors, including your health, how active you are and where you live.

Although no single formula fits everyone, knowing more about your body's need for fluids will help you estimate how much water to drink each day.

Health benefits of water

Water is your body's principal chemical component and makes up about 60 percent of your body weight. Every system in your body depends on water. For example, water flushes toxins out of vital organs, carries nutrients to your cells and provides a moist environment for ear, nose and throat tissues.

Lack of water can lead to dehydration, a condition that occurs when you don't have enough water in your body to carry out normal functions. Even mild dehydration can drain your energy and make you tired.

How much water do you need?

Every day you lose water through your breath, perspiration, urine and bowel movements. For your body to function properly, you must replenish its water supply by consuming beverages and foods that contain water.

So how much fluid does the average, healthy adult living in a temperate climate need? The Institute of Medicine determined that an adequate intake (AI) for men is roughly 3 liters (about 13 cups) of total beverages a day. The AI for women is 2.2 liters (about 9 cups) of total beverages a day.

What about the advice to drink eight glasses a day?

Everyone has heard the advice, "Drink eight 8-ounce glasses of water a day." That's about 1.9 liters, which isn't that different from the Institute of Medicine recommendations. Although the "8 by 8" rule isn't supported by hard evidence, it remains popular because it's easy to remember. Just keep in mind that the rule should be reframed as: "Drink at least eight 8-ounce glasses of fluid a day," because all fluids count toward the daily total.

Factors that influence water needs

You may need to modify your total fluid intake depending on how active you are, the climate you live in, your health status, and if you're pregnant or breast-feeding.

  • Exercise. If you exercise or engage in any activity that makes you sweat, you need to drink extra water to compensate for the fluid loss. An extra 400 to 600 milliliters (about 1.5 to 2.5 cups) of water should suffice for short bouts of exercise, but intense exercise lasting more than an hour (for example, running a marathon) requires more fluid intake. How much additional fluid you need depends on how much you sweat during exercise, and the duration and type of exercise. During long bouts of intense exercise, it's best to use a sports drink that contains sodium, as this will help replace sodium lost in sweat and reduce the chances of developing hyponatremia, which can be life-threatening. Also, continue to replace fluids after you're finished exercising.
  • Environment. Hot or humid weather can make you sweat and requires additional intake of fluid. Heated indoor air also can cause your skin to lose moisture during wintertime. Further, altitudes greater than 8,200 feet (2,500 meters) may trigger increased urination and more rapid breathing, which use up more of your fluid reserves.
  • Illnesses or health conditions. When you have fever, vomiting or diarrhea, your body loses additional fluids. In these cases, you should drink more water. In some cases, your doctor may recommend oral rehydration solutions, such as Gatorade, Powerade or CeraLyte. Also, you may need increased fluid intake if you develop certain conditions, including bladder infections or urinary tract stones. On the other hand, some conditions such as heart failure and some types of kidney, liver and adrenal diseases may impair excretion of water and even require that you limit your fluid intake.
  • Pregnancy or breast-feeding. Women who are expecting or breast-feeding need additional fluids to stay hydrated. Large amounts of fluid are used especially when nursing. The Institute of Medicine recommends that pregnant women drink 2.3 liters (about 10 cups) of fluids daily and women who breast-feed consume 3.1 liters (about 13 cups) of fluids a day.

Beyond the tap: Other sources of water

Although it's a great idea to keep water within reach at all times, you don't need to rely only on what you drink to meet your fluid needs. What you eat also provides a significant portion of your fluid needs. On average, food provides about 20 percent of total water intake. For example, many fruits and vegetables, such as watermelon and tomatoes, are 90 percent or more water by weight.

In addition, beverages such as milk and juice are composed mostly of water. Even beer, wine and caffeinated beverages — such as coffee, tea or soda — can contribute, but these should not be a major portion of your daily total fluid intake. Water is still your best bet because it's calorie-free, inexpensive and readily available.

Staying safely hydrated

Generally if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters (6.3 cups) or more of colorless or light yellow urine a day, your fluid intake is probably adequate. If you're concerned about your fluid intake or have health issues, check with your doctor or a registered dietitian. He or she can help you determine the amount of water that's right for you.

To ward off dehydration and make sure your body has the fluids it needs, make water your beverage of choice. It's also a good idea to:

  • Drink a glass of water or other calorie-free or low-calorie beverage with each meal and between each meal.
  • Drink water before, during and after exercise.

Although uncommon, it is possible to drink too much water. When your kidneys are unable to excrete the excess water, the electrolyte (mineral) content of the blood is diluted, resulting in low sodium levels in the blood, a condition called hyponatremia. Endurance athletes, such as marathon runners, who drink large amounts of water, are at higher risk of hyponatremia. In general, though, drinking too much water is rare in healthy adults who eat an average American diet.

Mayo Clinic Staff

Diet Soda and Metabolic Syndrome

Researchers have found a correlation between drinking diet soda and metabolic syndrome — the collection of risk factors for cardiovascular disease and diabetes that include abdominal obesity, high cholesterol and blood glucose levels, and elevated blood pressure.

Dietary Intake and the Development of the Metabolic Syndrome.
The Atherosclerosis Risk in Communities Study (Circulation)

The scientists gathered dietary information on more than 9,500 men and women ages 45 to 64 and tracked their health for nine years.

Over all, a Western dietary pattern — high intakes of refined grains, fried foods and red meat — was associated with an 18 percent increased risk for metabolic syndrome, while a “prudent” diet dominated by fruits, vegetables, fish and poultry correlated with neither an increased nor a decreased risk.

But the one-third who ate the most fried food increased their risk by 25 percent compared with the one-third who ate the least, and surprisingly, the risk of developing metabolic syndrome was 34 percent higher among those who drank one can of diet soda a day compared with those who drank none.

“This is interesting,” said Lyn M. Steffen, an associate professor of epidemiology at the University of Minnesota and a co-author of the paper, which was posted online in the journal Circulation on Jan. 22. “Why is it happening? Is it some kind of chemical in the diet soda, or something about the behavior of diet soda drinkers?”

By NICHOLAS BAKALAR
Published: February 5, 2008

 

What are the negative effects of caffeine?

The negative effects of caffeine are well documented, but not all research agrees on the results of caffeine. Some is specifically caffeine negative, citing numerous bad effects. Other studies take a more positive approach and cite both benefits and possible problems with caffeine consumption. Most studies correlate the negative effects with high caffeine intake, and with certain physical conditions or groups of people who tend to have more problems with caffeine.

A small amount of caffeine intake by a completely healthy person may have minimal effect. Caffeine is a stimulant and it will elevate heart rate, increase blood flow, and raise body temperature. It increases blood sugar levels and act as a diuretic, meaning you urinate more frequently and reduce water intake. Caffeine makes most users more alert, and some studies have suggested that it may reduce the risk of diseases like Parkinson's. People with certain conditions, or who consume large amounts of caffeine, may suffer more negative effects, however.

One of the negative effects of caffeine is that small amounts taken daily can create a physical dependence. If a regular coffee drinker, for example, fails to drink his daily dose of caffeine, he can end up with headaches, excessive sleepiness, a feeling like he cannot function. Withdrawal from caffeine can take anywhere from a few days to a few weeks depending upon how much caffeine a person customarily consumes.

When caffeine intake is above 300 milligrams a day, about three cups of coffee or three to four sodas, the caffeine may at first make a person feel energized. Yet one of the negative effects of caffeine is its ability to disrupt sleep cycles, causing less deep sleep, particularly when the person drinks caffeinated beverages within a few hours of bedtime. So while a person may be using coffee or other caffeine laced beverages to "get started" in the morning, one reason he might need this extra boost because he is getting inadequate sleep.

In 2006, studies on night shift workers found that those who consume caffeine at night are most prone to this effect. Since night shift work already disrupts normal sleeping patterns, caffeine intake may create more serious issues. Those who drink caffeinated beverages and work the night shift have a far greater likelihood of getting insufficient deep sleep during the day. This can result in a continued cycle of exhaustion and caffeine boosts, a greater dependence on caffeine, and more caffeine consumed, which only exacerbates the problem.

Certain people are also particularly caffeine sensitive and more likely to experience negative effects of caffeine. For example, some people will feel "buzzed" or hyped up from one cup of coffee. Lower body weight tends to translate to higher likelihood of experiencing the negative side effects.

People with panic disorder or generalized anxiety disorder are much more prone to reacting badly from increased heart rate. Caffeine, even in small doses, can create panic attacks and interfere with medications taken to calm the system. Caffeine is a adenosine-receptor antagonist, meaning that it blocks the receptors in the brain that bind with the neuromodulator adenosine, which slows neural activity. It also promotes the release of adrenaline anddopamine.

For people with high blood pressure or high blood sugar levels, the negative effects of caffeine should be understood. Caffeine can raise both these levels. Any type of heart problem can be affected by caffeine. The negative effect of caffeine in increasing heart rate can create problems for people with heart conditions, and in high doses, caffeine can induce irregular heartbeats in healthy people.

People with stomach conditions like irritable bowel syndrome, Crohn's disease, ulcers, and gastro-intestinal reflux, may all suffer from consuming caffeine. Caffeine increases acidic response in the stomach which may lead to excessive bowel movements and is associated with stomach discomfort.

Negative effects of caffeine can be broken down into moderate and serious side effects:

Moderate effects include:

  • Headaches
  • Irritability
  • Increase in breast tenderness
  • Restlessness
  • Mild insomnia
  • Increased heart rate
  • Increased blood sugar
  • Difficulty concentrating
  • Mild stomach upset

 

Severe effects include:

  • Panic attacks
  • Irregular heartbeat
  • Sleep deprivation
  • Continuous stomach problems
  • Prolonged depression
  • Sleep disorders

 

Though there are some positive effects of caffeine, the negative should be understood. Anyone in a high-risk group should be aware of the severe negative effects. People with mood disorders, high blood pressure, diabetes, heart disease, kidney disease, chronic intestinal issues, work the night shift or who are pregnant should minimize caffeine intake.

WiseGeek

Do Diet Foods Lead to Weight Gain?

If you think you're cutting calories by eating diet or low-calorie versions of your favorite foods, think again. A new study by Canadian scientists published in the journal Obesity suggests that our bodies can't be fooled that easily.

Led by David Pierce, researchers at the University of Alberta studied the eating habits of young rats, and found that they tended to overeat when they were fed "diet" foods. Though the new study was conducted in animals, it adds to a growing body of research in humans that suggests a diet-foods paradox: the more low-calorie (or even zero-calorie) sodas and foods you consume, the more your body demands payback for the calories it was deprived.

Pierce and his team started with the assumption that animals, and young animals in particular, are adapted to crave high-calorie foods that are packed with fat and carbohydrates, the crucial biological fuel that rapidly growing juveniles need. Using classic Pavlovian conditioning techniques, Pierce trained his rats to associate low-calorie foods with a "diet" taste, and high-calorie foods with a different taste. So, when the rats were fed a high-calorie food that had been flavored with the diet taste, their brains assumed that their bodies were running low on calories. These animals then overate at their next meal in an effort to refuel and make up for the lost energy. "Animals have the ability to sense the caloric value of food they take in," says Pierce. "We found out that an animal can learn to use flavors to predict calories in an attempt to achieve energy balance."

This same phenomenon could explain similar results in recent studies of dieters, says Pierce. Two years ago, scientists at the University of Texas reported in an eight-year study that for every can of diet soda that a person drank, he raised his risk of being overweight by 41%, compared to a 30% increase in drinkers of regular, sugared drinks. Earlier this year, another study of diet-soda drinkers came to a similar conclusion, this time about metabolic syndrome, the dangerous constellation of risk factors, such as obesity, high cholesterol and insulin resistance, that increases the likelihood of heart disease. In this report, part of the 60-year-old Framingham Heart Study, researchers found that soda drinkers, regardless of whether they consumed diet or regular beverages, had a 48% higher risk of metabolic syndrome than non-soda drinkers.

At the time, even the study authors conceded that it was impossible to implicate diet drinks completely, since it's possible that those who drank low-calorie beverages were already overweight or at higher risk of metabolic syndrome, and chose the diet drinks in an effort to get healthier. But Pierce's work hints that a more basic, biological mechanism may be at work. The animals in his study were able to predict the amount of calories in a food based on taste, demonstrating that the body uses cues like taste and texture to make sure it's getting enough fuel. Just as Pierce's rats were fooled into thinking they hadn't absorbed enough calories after eating diet chow, people are preprogrammed to anticipate sugary, high-calorie fulfillment when drinking a soda or noshing on a sweet-tasting snack. So, the diet versions of these foods may leave them unsatisfied, driving them to eat more to make up the difference.

All of this emerging work could make the food and beverage industry, which has invested billions in diet and low-calorie versions of almost every food imaginable, a bit uneasy. "This study simply defies common sense," wrote Dr. Richard Adamson, scientific consultant to the American Beverage Association, in a prepared statement responding to the study. "To suggest that foods and beverages with zero calories contribute to weight gain contradicts the overwhelming body of scientific evidence that supports that they can help you reduce calories and maintain a healthy weight."

Dr. Ramachandran Vasan, lead author of the Framingham study, however, notes, "A zero-calorie drink could produce a metabolic response if it is sweet. It can condition you to develop a preference for sweet things, which can lead to weight gain or metabolic syndrome. So something that is sweet could produce a metabolic effect even if it doesn't have a whole lot of calories.

Of course, none of the studies has yet proved that diet foods or beverages actually cause weight gain or heart disease; they have merely found an intriguing association, which scientists are still trying to explain. Well, nobody ever said counting calories was easy.


By Alice Park Wednesday, Aug. 08, 2007