Dr. Day is a cardiologist and Medical Director of Heart Rhythm Services at his practice in Salt Lake City, Utah. He graduated from Johns Hopkins Medical School and completed his residency and fellowship in cardiology at Stanford University. He is board certified in Cardiology and Cardiac Electrophysiology.
How Much Water Should You Drink?
Everyone knows the answer to how much water should you drink is eight glasses, right?
In this article, I will answer how much water should you drink and debunk the top 10 hydration myths based on the latest medical science.
The Top 10 Hydration Myths
1. Drink 8 Glasses of Water
The biggest hydration myth is that you must drink eight glasses of water every day. Even my children have been taught this in school.
Guess what, no medical study has ever shown that you need eight glasses of water. The best medical studies I could find recommended five and six glasses daily.
The first was a study of 20,297 Seventh Day Adventists which showed that drinking five or more glasses of water each day was associated with a 50% decreased risk of a heart attack.
The second study, recommending six glasses of water, included 47,909 people. In this study, those drinking six or more cups of water were observed to have a 51% lower risk of bladder cancer compared to people who only drank one cup daily.
Both of these studies should be interpreted with caution as they were just observational studies. These studies don’t prove that water was the reason why people had less heart attacks or bladder cancer. An alternative explanation for these findings is that water drinkers tend to be more health conscientious, eat a healthier diet, and are more likely to exercise regularly.
So where did the 8 glasses a day myth originate? My best guess is that it came from a 1945 publication by the National Research Foundation. This 1945 report wasn’t based on any medical studies. Since 1945, the recommendation has become urban legend and the rest is history.
2. Caffeinated Drinks Dehydrate You
The second biggest hydration myth is that caffeinated drinks dehydrate you. When put to the test in a medical study, this was simply not true.
In fact, there was no significant difference in how well a caffeinated drink, like a carbonated beverage or coffee, hydrated you compared to water. While I would never recommend that you drink anything other than water, the take home message of this study is that any drink hydrates you.
3. You Can’t Drink Enough Water
With all of the sensationalized media reports every summer of people dying from dehydration, many people now carry huge water jugs and drink water all day long. Can you get too much of a good thing? Yes.
There is actually a medical condition called water intoxication. If you drink too much water it can cause hyponatremia. Hyponatremia occurs when sodium levels are too low in the blood. When this happens it can cause confusion, brain swelling, and even death.
Interestingly, one study found that 13% of Boston Marathon runners had hyponatremia. This is because they over hydrated with water and sports drinks. Over compensating with fluids, following massive sweat losses, caused dilution of their blood and resulting hyponatremia.
The key point of this study is that drinking fluids in moderation is best for endurance athletes. You don’t want to over hydrate with endurance events.
4. You Need Sports Drinks When Exercising
Does the risk of hyponatremia with exercise mean that you need to start drinking Gatorade when working out? Absolutely not. In fact, studies show that sports drinks don’t protect you from hyponatremia.
Sports drinks are nothing more than sugar water with a few electrolytes.
Fortunately, even if you sweat a lot, you can get all the electrolytes you need from eating real food. For example, you can get all the magnesium you need from nuts, seeds, and greens. Table salt or tomato juice will get you your sodium. Fruits and vegetables pack in the potassium.
5. You Can’t Rely on Your Thirst
Many Internet reports will tell you that you can’t rely on your thirst. According to these reports, once you are thirsty it is too late. You are already dehydrated.
However, that is not the opinion of the world’s leading scientists on this issue. As published in the Clinical Journal of Sports Medicine, the world’s leading scientists came to the conclusion that thirst is the best way to know if you need water or not in an athletic competition.
The take home message here is that if you are thirsty, you are probably low on water but not yet to the point of dehydration. Indeed, many leading scientists feel that if marathon runners simply let their thirst guide rehydration, hyponatremia could largely be avoided.
6. Drink Until Your Pee is Clear
You’ve heard the recommendation, keep drinking until your pee is clear. The reality is that if your urine is totally clear then you are probably over hydrated. Ideally, your urine should be pale or have a slight color to it.
7. Yellow Urine is a Sign of Dehydration
It is true that your urine is yellow when you are dehydrated. However, it is also true that if you are taking a multivitamin containing riboflavin, or vitamin B2, your urine will also be yellow. Thus, the only time yellow urine is a sign of dehydration is if you don’t take a multivitamin.
8. Drinking Extra Water Gives You Beautiful Skin
Once again, Internet reports and articles in women’s magazines would have you believe that if you drink water all day long your skin will be beautiful. Unfortunately, there is no proof. Indeed, a study looking at skin beauty and water consumption found absolutely no relationship.
9. Drinking Extra Water Flushes Out Toxins
Of course, you need to drink the right amount of water for your kidneys, and the rest of your body, to do its job. However, there is no scientific proof that drinking more water than what your body needs helps the kidneys to flush out toxins. The one possible exception is that in those with a history of kidney stones, drinking extra water may help to prevent further stones from forming.
10. Food Doesn’t Count as Water
Studies show that even on the Standard American Diet, which is very low in fruits and vegetables, you can still get 22% of your water needs just from food. Of course, studies also show that people in Asia and Mediterranean countries, where fruits and vegetables are commonly eaten, can get much more of their water needs from food.
How much water should you really drink?
Feeling confused? You’re not alone.
The truth is that everyone is different. Depending on your size, the temperature, how active you are, your food choices, etc. you will need a different amount of water each day.
There is no universal recommendation on how much water you should drink. Be curious. Observe your body. You will learn exactly how much water your body needs.
Rather than focussing in on a specific number of glasses when it comes to hydration, studies show that common sense is best. Here are my four common sense tips:
1. Have a glass of water soon after awakening in the morning.
2. Drink if you’re thirsty.
3. Quickly rehydrate if your urine is too concentrated.
4. Drink more if you are sweating.
How do you make sure you get the right amount of water your body needs? Please leave your experiences below for everyone to learn from. As always, I’ll do my best to answer any question posted.
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Disclaimer Policy: This website is intended to give general information and does not provide medical advice. This website does not create a doctor-patient relationship between you and Dr. John Day. If you have a medical problem, immediately contact your healthcare provider. Information on this website is not intended to diagnose or treat any condition. Dr. John Day is not responsible for any losses, damages or claims that may result from your medical decisions.