#071 Do You Really Need 8 Glasses of Water Daily?

February 2nd, 2015 by

Do You Really Need 8 Glasses of Water Daily?

Your mother probably told you to drink 8 glasses of water each day. Many health “experts” also recommend getting at least 8 glasses (64 ounces or about 2 liters) of water each day.

Are you wondering if there’s actually any science backing up this advice?  Just how much water should we be drinking to lose weight and maintain optimal brain and heart function?

What the Science Tells Us about 8 Glasses of Water

You might be surprised to learn that there are actually no medical studies backing up the practice of drinking 8 glasses of water each day.  While there have been studies done on this subject, none of these studies to date have shown any significant benefit.

If there are no data supporting the medical need to drink 8 glasses of water each day then the question naturally arises, how much water should you drink?  The simple answer is, it depends.  In this article we will explore possible reasons why you may want to increase your water intake depending on your weight, brain, and heart goals.

How much water should you drink to stay hydrated?

It appears that the amount really depends on the individual person, where they live, and how active they are. Adults who live in an average climate and are moderately active can likely maintain their health drinking less than 8 glasses per day.  This doesn’t mean that you want to skimp on drinking your water however.

In contrast, those people who exercise frequently or live in very hot climates can lose up to 4 liters of fluid in just one hour of intense exercise on a hot day.  For these people, staying hydrated during a work out is critical for their health and to prevent a heat stroke.  These people could easily drink far more than 2 liters of water in a day.

Why is water so healthy?

Did you know that water makes up about 70% of your body?  Water helps to flush toxins from your bloodstream and cells, allowing your body to experience a daily “detox.”

Staying hydrated is also important for maintaining your energy, getting a good night’s sleep, and keeping your mood up.  If you want to appear young, water can also play an important role.  For example, if you are not drinking enough water, you may appear aged and can suffer from rough or cracked skin, bloating, or puffiness.

Can you really tell the difference between hunger and thirst?

Strangely, medical studies have shown us that we often cannot tell the difference between hunger and thirst. Unfortunately, most of us end up eating something when we really may just be thirsty.

Water helps us to feel full because it takes up a lot of volume in our stomachs.  Sometimes we may think we are hungry, and may even experience hunger pains, but in fact it may be that we are just experiencing mild dehydration.

When we don’t stay hydrated, we don’t feel the best that we could.  We tire easily, feel moody, get headaches, and we don’t function well overall. These uncomfortable feelings make us crave food because we are looking to food for more energy when all we really need is more water.

Water can help us to eat less at meal times as well. Try drinking 2 glasses of water right before you eat a meal and you may find you eat less since your stomach will feel partially full and you won’t be confusing thirst for hunger at all.

Why do water drinkers stay thin?

Have you ever noticed that people who carry a water bottle around with them seem to appear healthier and slimmer than most people?  What is the science behind water drinking and maintaining a healthy weight?

Besides not confusing hunger for thirst, the obvious answer is that if you are drinking a lot of water you probably are not drinking soda pop, fruit juice, or other sugary drinks.  This alone could cause significant weight loss.  I commonly see patients lose more than 20 pounds just by giving up all soda, fruit juice, sports drinks, and other sugary drinks.

Even diet soda may cause significant weight gain in many studies!  Studies show that even though you are not getting any “calories” from diet sodas, the aspartame in diet sodas is feeding your bad gut bacteria which, in turn, may cause weight gain.

Water also causes a significant calorie burn through the process of cold thermogenesis.  If you want to learn more about how to boost your metabolism through cold thermogenesis, I recently wrote an article on this subject (blog #68).

Studies have shown that by drinking 8 glasses (2 liters) of cold water, your body can be forced to burn an extra 400 calories!  Researchers report that most of this 400 calorie weight loss was due to the energy required by the body to heat the cold water up to body temperature.  If you do the math, drinking 2 liters per day of cold water, without increasing your food intake, would burn 42 extra pounds per year.

Since there is no risk in drinking more water for most people (see disclaimer at the bottom of this article), and you might even feel more energetic thereby increasing your work out routine, why not start drinking more water today?

Boost Cognition and Memory with Water

Could helping your child score well on the SAT or ACT college entrance tests be as simple as drinking more water?  Studies have consistently shown that children do better on tests when they are hydrated.  Even adults, based on medical studies, do better on cognition tests when they are well hydrated with water.

Other studies have shown that dehydration, or even relative mild dehydration like not drinking enough water during the day, can impair brain function.  Studies have even shown that fighter pilots don’t fly their planes as well if they are not drinking enough water.  Thus, if you want optimal brain and memory function learn to love water.

How much water should you drink to prevent heart disease?

If your goal is to prevent heart disease and never see a cardiologist, like me, then there are actually some data supporting how much water you should drink.

The Seventh Day Adventists are one of the healthiest groups of people in the world.  The Adventists have been extensively studied and have even been featured in the best selling health book, Blue Zones (affiliate link).

In this study, researchers closely followed 20,297 California Adventists for 6 years.  Interestingly, they found that those Adventists drinking 5 or more glasses of water each day were 54% less likely to die from heart disease!

Just how does water protect against a heart attack?  Could the benefit from water be because they drank water rather than soda pop, fruit juice, or other sugary drinks?  Likewise, could a high water intake be a manifestation of someone who is generally more health conscientious or someone who exercises a lot?

There are some studies that suggest that relative dehydration can cause you to have “thicker blood” or a higher blood viscosity.  If you are not drinking enough water then your blood particles are more likely to clump together and form clots.  These clots could lead to a heart attack or a stroke.  Regardless of how you can prevent a heart attack by drinking more water, it seems to me that drinking at least 5 glasses of water each day is a very healthy habit which we should adopt.

Dr. Day’s 6 Water Rules

To help you maintain a healthy weight and allow your brain and heart to function at its best, let my give you my six rules when it comes to drinking water.

1. Drink water instead of soda, fruit juice, or other sugary drinks

If you want to torpedo your health and your waist line, then drinking soda in either the high fructose corn syrup or diet varieties, juice, or other sugary drinks like sports drinks is a great strategy.  On the other hand, if you want to feel energized and maintain a healthy weight learn to love water.  If water isn’t yet your thing, try adding some fresh lemon or lime to your water.

2. If you are hungry between meals drink water first

Learn to notice the difference between your body’s true hunger signals, versus thirst signals. If you feel hungry between meals, try drinking something first. Wait 30 minutes. If you still feel hungry after 30 minutes, you probably are hungry and should eat something.

3. Drink water to boost your metabolism

To keep your body’s metabolism high, stay hydrated.  As discussed in this article, you can burn a significantly high amount of calories each day by drinking 2 liters of water.

4. Stay hydrated for optimal brain performance

Our brains require plenty of water to function optimally.  Stay hydrated to boost your cognition and memory.

5. Drink at least 5 glasses of water daily for your your heart

While 8 glasses of water (2 liters) has not been shown to make you “healthier,” there are data that drinking at least 5 glasses of water each day may protect your heart.  This may keep your blood viscosity low and prevent clots from forming.

6. Keep water with you throughout the day

As it is so easy for us to become dehydrated through the day, learn to carry a glass or stainless steel water bottle.  Having the water bottle with you is a great reminder to drink more.

How much water do you drink each day?  Do you carry a water bottle with you?


Please remember that if you suffer from heart failure, kidney failure, or other medical conditions you should discuss your optimal daily water intake first with your physician.