The 8 Glasses of Water a Day Myth
In 1945 a US research paper said we should drink six to eight glasses of water a day, a recommendation that many in the health care and fitness industry endorse. Others say to let thirst be your guide. There is also a belief that except for extreme environment conditions or after long periods of exercise, as long as you’re eating healthy the optimal number of glasses of water needed for optimal health may be zero. Let’s take a closer look.
Starting with the recommendation to drink the eight glasses of water a day, a research review published in 2002 in the American Journal of Physiology found that there were no scientific studies to support this opinion. Nine years later the author of the study, Dartmouth Medical School physician Dr. Heinz Valtin, reported that he still had not found any data to support this guideline.
One popular recommendation for determining water consumption is to simply let thirst be your guide – if you’re thirsty, drink up! The problem is that by the time you feel thirsty, you may already be dehydrated. If you’re exercising, this dehydration may result in dizziness, excessive fatigue, and more serious health concerns.
According to a paper published by the National Federation of State High School Associations in 2011, “Unrestricted access to water or sports drinks should lead to the consumption of four to eight ounces of (one-half to one cup) of fluid every 15 minutes.” The paper goes on to say that at moderate intensity exercise, “the human body generally produces 0.5 to 1.5 liters of sweat in one hour, but this may be higher in some individuals.”
One formula for determining how much water you should consume daily is as follows: “Bodyweight (in pounds) divided by 2 = ounces of water per day.” If you weigh 150 pounds, this comes out to 75 ounces per day (150/2 = 75). However, for optimal function, it has been suggested that the results of this formula need to be increased by 20 percent, which in our example would mean a recommendation of 90 ounces a day.
How much water do we really need? To answer this question, consider that a newborn is about 70-80 percent water by bodyweight. Adult women are about 55 percent water and men about 60-70, but as we get older we become less efficient at staying hydrated and those numbers decrease for both sexes. The issue is that to keep its tissues hydrated, the body needs electrolytes – drinking plain water isn’t enough.
Electrolytes are salts that when dissolved in water split into molecules called ions. The most common electrolyte in your body is sodium chloride, or table salt. Ions allow electrical impulses to travel throughout the body. Among many other functions, these electrical impulses enable your muscles to contract; as such, if your diet did not contain electrolytes your heart would stop.
Sodium is an electrolyte that controls how much water is outside the cells, whereas potassium is an electrolyte that controls how much water is inside the cells. Of course, water is necessary for hydration to occur, but if the electrolyte concentrations are not balanced the water you consume may be quickly excreted out of the body, taking electrolytes with it. In effect, drinking water can actually cause dehydration by diluting the body’s level of electrolytes. For this reason, the best sports drink are designed to contain the optimal concentration of the electrolytes sodium and potassium.
Keith R. DeOrio, a medical doctor who has done extensive research on hydration, says we can learn a lot about how to properly hydrate by observing the behavior of animals. He says animals seldom go to streams and watering holes to hydrate themselves because they consume all the water they need, and with the optimal concentration of electrolytes, from the food they eat. He says that at one sitting a tiger can consume as much as 80 pounds of food in one meal, and because meat is raw, 64 pounds of that meal will be water.
This is not to suggest that you should never drink water, as there are many conditions (such as extreme heat or strenuous exercise) where it would be unhealthy not to at least drink water. Rather, by focusing on consuming a diet high in raw foods (such as fruits, vegetables and sushi) then you will have enough electrolytes in your system to be able to keep the water in your system.
If you need to boast your water intake, consuming more fruit and vegetables is the optimal way to hydrate – although with exercise, consuming additional water may be necessary. As for fruit and vegetable juices, many of these use filtering processes that can strip away the electrolytes and other vital nutrients. Some also contain added sugar to enhance their flavor.
Another issue is consuming processed foods. One of the primarily additives in food is salt, and consuming large quantities of these foods will upset the electrolyte balance and prevent water from entering the cells. One obvious example is sodas, which often contain salt (some much more than others) that will increase thirst, but you don’t taste it because of the sugar. This presents an endless cycle of drinking more soda to quench your thirst, and the salt causing you to become thirstier.
Sports drinks are certainly a popular choice for exercising. The general recommendation is that a sports drink should contain 6-8 percent carbohydrate, along with electrolytes to ensure that the water can be used by the cells. Again, if you’re consuming a healthy diet, consuming additional water should not upset the natural electrolyte balance.
The bottom line is that the recommendation to drink six to eight glasses of water does not apply to everyone and for all conditions. The best approach is to eat healthy and ensure proper hydration with water and sports drinks when necessary.