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Can Dehydration Affect Our Mood?

Water is by far the number-one nutrient in our diet. Studies have suggested that proper hydration may lower our risk of heart disease and cancer, and may even make us better kissers. Brushing artificial skin against the lips of young women, researchers found that hydrated lips showed greater sensitivity to light touch.

Although it is well known that water is essential for human survival, it’s only recently that we have begun to understand its role in the maintenance of brain function. It makes sense. Our brain is 75% water. When we get dehydrated, our brain actually shrinks. Even mild dehydration, which can be caused by simply exercising on a hot day, has been shown to change brain function.

I’ve talked about the role of hydration for cognitive function in Does a Drink of Water Make Children Smarter?, but current findings suggest that our mood states may also be positively influenced by water consumption.

The effects of dehydration in real life have not been not well documented. It wasn’t until 2013 that the first study to investigate the effects of mild dehydration on a variety of feelings was published. What did the researchers find? The most important effects of fluid deprivation were increased sleepiness and fatigue, lower levels of vigor and alertness, and increased confusion. But as soon as they gave the subjects some water, the deleterious effects on alertness, happiness, and confusion were immediately reversed.

Water absorption actually happens very rapidly, within 5 minutes from mouth to bloodstream, peaking around minute 20. Interestingly, the temperature of the water appears to affect this speed. Which do you think is absorbed more rapidly—cold water or warm, body temperature water? It turns out cold water gets sucked in about 20% faster!

How can we tell if we’re dehydrated or not? Well, why don’t we ask our bodies? If we chug down some water and then turn around and just pee it all out, presumably that would be our body’s way of saying, “I’m good, all topped off.” But if we drink a bunch of water and our body keeps most of it, then presumably our tank was low. Researchers from the University of Connecticut formalized the technique. You empty your bladder, chug down 11 milliliters per kilogram of body weight (about 3 three cups of water for an average-sized person) and then an hour later see how much you pee. Basically, if you drink 3 cups and pee out less than 1, there’s a good chance you were dehydrated. You can see the findings of this chug-and-pee test around minute 3 in my Can Dehydration Affect Our Mood? video.

For more on water, see my How Many Glasses of Water Should We Drink a Day?Does a Drink Of Water Make Children Smarter?, and Treating Dry Eyes with Diet: Just Add Water? 

Other healthy beverages include hibiscus tea (Hibiscus Tea vs. Plant-Based Diets for Hypertension) and green tea (Dietary Brain Wave Alteration and Benefits of Green Tea for Boosting Antiviral Immune Function).

What else can affect our mood?

What about the omega-3s in fish? That’s the subject of another video: Fish Consumption and Suicide.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

40 responses to “Can Dehydration Affect Our Mood?

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    1. I was advised to drink at least 1 quart and up to 1 i/2 qts. You can also drink too much. My blood sodium was diluted from too much. Too little can affect bowel movements.

  1. Great to know about the drink test and our brains being 75% water. I had heard that brain alertness relies more on water than coffee and now I know why. I sure feel the difference me. Dr. Greger also taught us about the importance of clean water.

    A proud monthly supporter of

    1. The brain is 75% water, according to Dr. Greger, and 60% fat according to most other sources. That doesn’t leave much room for logical thought, does it?

      1. i think you really don’t understand those statements.

        ~ 78% of the total matter of your brain is water
        ~ 60% of the solid matter of your brain is fats (not the typical fat cells in the body)
        both are perfectly logical and factual statements. that is fats are ~12% of the total matter which is ~60% of the ~22% solid matter

  2. So totally agree! Hydration has everything to do with brain function, including our mood.

    Two thoughts. One is that cold water forms mucous in the throat and perhaps other mucous membranes on the way to the stomach. It would seem (and I have read) that the stomach would hold onto cold water until it’s body temperature before releasing it into the system.

    Also, if we have a bunch of caffeine in our system, it will act as a diuretic and we will excrete lots of water even though we are not well hydrated. If we use caffeine, we need more water than if we were drinking only water. Unfortunately, many drink only caffeinated drinks and NO water.

    We need pure water, the original 0 calorie beverage.

    1. Hi Barbara – I have heard that information before about cold water, mucous, and the stomach “holding onto” the water to bring to body temp before releasing it into the system. As a physiologist, I am very interested in the research studies that support this information. Any chance you have some links to research? We often hear of information of this ilk that circulates but trying to find out the science and facts about it are sometimes nebulous. Given that this site is about science and fact based information, I would appreciate seeing the research. Otherwise it may have to go into the stockpile of urban myth. I so look forward to seeing the research! Thanks!

      1. I found this research re: emptying rate of the stomach and temperature of the fluid:

        “Temperature of drinks does not seem to have an effect on the rate of gastric emptying and intestinal absorption. ”
        Other information states that it only takes about 5 minutes for the consumed liquid to come to body temperature anyway and thus becomes a mute point (which makes sense to me). I could find no research on the publishing site for scientific information supporting the suggestion that cold water causes mucous development.
        Anybody else have any supporting research? Thx!

    2. Alcohol also acts as a diuretic. It’s a good idea to drink a glass of water between each drink, if you’re into that. In fact, many of the morning after negatives are from dehydration.

      I’ve been rereading parts of The Blue Zones, starting with the chapter on Ikaria. The beginning of the chapter starts with the story of a man who was a native of Ikaria, but had moved to the US as a young man. In his 60s he was diagnosed with lung cancer, told to go home and make out his will. He decided to move back to his native home, because it would be cheaper to be buried there. Well, he went home, ate his native foods, including a pretty substantial amount of homemade wine, reconnected with old friends, started feeling better and eventually got well. At the time the book was written he was 100 and had long since outlived all his US oncologists. I wonder how much water he drinks, along with all that wine he makes and drinks.

  3. It is more complex. Electrolyte imbalance comes from drinking too much water and peeing too much water (polyuria) but not replacing the sodium expelled. It could make you more dehydrated by osmosis. This condition could cause problems with the nerves.

    1. Panchito – although what you are saying is technically accurate, . . .it takes a boatload of water to cause this much disruption to the homeostatic balance in the body. Death from water over consumption has occurred, but those have been extreme events. If I ask myself if anyone I know or heard of has died from water over consumption of been hospitalized for such, I would have to say I know of no one. I am aware of individuals consuming salt pills who worked on outdoor construction projects in extreme heat and needed to drink copious amounts of water to endure the heat. But this is not the norm for most individuals on balance. I hear more about deaths due to extreme dehydration and over heating.

      1. Hyponatremia is a pretty common presentation to ED’s, and is relative excess water consumption that hasnt been balanced with electrolyte intake. It occurs in athletes or outdoor workers, and even persons who engage in non competitive intense exercise, who drink stacks of water, though no salts, so to speak. The electrolyte imbalance leads to cardiac dysrhythmia’s, and if unaddressed, cardiac arrest.

      2. Of great interest, would be whether Dr.Greger has examined the linkage between Sudden Cardiac Arrest and the regular consumption of softwater(vs hard water),reversed osmosis treated water,or distilled water.

        The issue to be examined would include for the most part,the stripping of the body’s basic mineral and nutrient base,by the unnaturally increased solvency or solubility capacity of the ingested treated water, at a rate which cannot be replenished by mineral or nutrient supplementation.

        It would follow that ingestion of water, depleted of its mineral and nutrient base in treated or naturally occurring soft water would disrupt the internal electrolytic base of the body disrupting the transnission of crucial electrical heart signals, thereby leading to Sudden Cardiac Arrest.

        To a large degree this might explain the growing divergence between Sudden Cardiac Arrest
        absent of classic heart disease symptoms.

        Perhaps better for men to drink ordinary tap water at the risk of enhancing breast growth.In my particular case,I have switched to hard well water from reverse osmosis water ingestion ,after succumbing to Sudden Cardiac Arrest,for which only the heroic efforts of Mackenzie General Hospital in Ontario Canada brought me back after being gone for 14 minutes.

        I remain without classic CVT symptoms,and without any other identifiable markers.

  4. Hi Rebecca,
    Thanks for mentioning this. Although it is so sad to hear that a mother lost her life by doing the fast and high amount of water competition, it can be a lesson to others not to be pressured into these type of competitions.
    Thanks to Dr Gregor for this article and about hydration and its importance. It is time for a glass of water!

  5. Hello, I am writing to ask for any and all input on a completely different twist on the idea of drinking water. Until recently, I never knew there is even a medical “condition” associated with this: I have absolutely ZERO thirst. Never. Ever. Drinking water is a huge chore for me, as I have to force it down. Even then, I find I hold it in my mouth for a while before I can actually “work up” to swallowing it. I have no idea what in the world I can do to “stimulate” my thirst. The response is entirely gone. Even if I am out in the heat, or walking for a long while, I have no impulse to drink. Very strange, and very frustrating. Please, I welcome any feedback about this that could possibly return me to how I felt as a child, playing outside, and running in for that cool drink of water….always took thirst for granted. Thank you!

    1. Please don’t take this as being flip or trying to be cute… but try eating some cold watermelon from the fridge. I’m not saying it would help you return to drinking water, but at least it would help keep you hydrated.

      Also, you could try drinking something like distilled water. Perhaps there is something in the water you drink that your body finds offensive.

      1. Thank you for trying. I have been drinking distilled water for 30 years.

        I like watermelon a lot, but I’m not sure it can provide me with all the hydration I need.

        I appreciate your help.

        1. Also, I lived with a parent for twenty-five years or so and never saw her take a drink of water. But she would often stir up some drink or another like coffee or hot tea and drink that alone or with cookies of some sort. She lived to be 102.

  6. Dr Greger,

    what do you think of fruitarians who believe that we don’t need water apart from the water present in fruit? There are some folks who believe that we should eat a ton of fruit, especially varieties with lots of water like watermelon, citrus etc and that will take care of our fluid needs.Would love to know your thoughts.

    1. May,

      even if you choose fruits with very high water content (90%), you would still need to eat over 2200 grams of fruit to get 2000 milliliters of water! That’s very hard to reach.

      Hope this helps,

      Moderator Adam P.

  7. I used this formula from Mayo’s site and after several run throughs, I get the same answer 31 cups – 247 oz of water a day?
    What am I doing wrong other than being overweight?
    217 lbs – 71 years old.

    The formula for how much water you should be drinking:
    Step 1: Take your weight (in lbs) and divide it by 2.2. (217/2.2 = 98.6)
    Step 2: Multiply that number by your age. (98.6 x 71 =7003)
    Step 3: Divide that sum by 28.3. (7003/28.3 = 247)
    Step 4: Your total is how many ounces of water you should drink each day.
    Divide that number by eight to see your result in cups.

    1. something is wrong where you multiply by age , try those same numbers for a 21 year old and 120 lb and i got 5 cups of water , just because your older should not mean that much water. junk formula i would say

    2. Hi Ray. According to the recommended adequate intake (AI) you should drink 3.7 litres/day which is 130 oz (see here). Try using other water intake calculators. There might be something wrong with the formula.

  8. I question the fact that water is absorbed 20% faster if it is cold. This does not agree with what we already know about digestion. The stomach holds all liquid until it warms up to body temperature before releasing it through its valve. Could it be that this data has been altered by those who would have us eat all raw?

  9. Water is the greatest hydrator. For us plant-basers, other fluids also are important on a regular basis. Breakfast with soy or almond milk on cereal, or with meds & vitamins to start the day. Decaf coffee, teas, hot and cold, and soups.. At dinners we split a bottle of craft ale making that meal more enjoyable, continuing mealtime tradition.

    Hydration along with lots of veggies and fruits which also have large water content not only keep us from dehydrating, but aid digestion and normalize body functions. Since I recently have become more aware of the importance of a plant based regimen, laxatives no longer are a necessary part of daily life.

  10. I read in Wikipedia that people with eczema (which I have) lose moisture at an accelerated pace. I have difficulty staying hydrated; I don’t get thirsty but then realize how dry I am. During the day I drink mostly weak tea (black and green together). I drink 3-4 cups of water in the course of a night but still wake up dehydrated. I would appreciate any helpful suggestions.

    1. Tom Brady (American football player) claims to drink over 2 gallons of water per day and said he doesn’t sunburn anymore since staying hydrated. Of course, Tom Brady sweats a lot as he plays football in the season and works out off-season.

      Oh, and he sells electrolyte drops to put in the water. ‘-)

      Personally, I keep cookies nearby (coconut macaroons, ginger snaps, and others) and a jug of water and glass as well. By eating a few bites of cookies, I feel the need to wash them down with either tea or straight distilled water.

      As for the eczema, I’ve got some leftover bottles of unadulterated cranberry juice. I’ve had a crusty spot on my hand and some small bumps on my elbows for some time. On a whim I substituted the cranberry juice for the green tea suggested by Dr Greger here in a video or blog as a skin treatment.

      The green tea helped but the cranberry juice gave the result I was looking for. I put it on whole body, left it for about 30 minutes, then rinsed it off. Skin exfoliated and smoothed up… that is, rolled off the little bumps I would normally feel.

      I’m probably going to do this once a week for the rest of my life.

    2. Hi Gracia. I am a volunteer with The adequate intake (AI) for women is 11.5 cups (about 2.7 litres) of water. Drinking that much helps you keep hydrated. I suggest using an app e.g. Waterlogged or iHydrate, that can remind you to drink water and track your daily water intake. Remember that about 20% of your water intake comes from fruits and vegetables. So, also try eating fruits with a high water content e.g. watermelon, strawberries, grapefruit, orange etc.

      I hope that helps.

  11. have anyone tried a 5-htp supplement for a natural mood management ? I’ve come across this article and think it’s worth a try …

    1. Bara, I too have read the research on 5htp converting to serotonin and melatonin. I’ve been taking it for several months before sleep and while I slept well before, I feel this is a good addition to night time supplementation.

      Another one I now take after reading or seeing something from Dr. Greger, is saffron. I think this is worth the price when taken for mood.

      I also take Ashwagandha at night (can’t remember why but read something) White Willow Bark to help fight inflammation, and magnesium to guard against foot cramps, and Naringin as it somehow is a helper to fight a beta and tau… all as a night time regimen.

      Also have liquid melatonin when I need to sleep fast and wake up well rested, to add to water before going to bed.

    2. Thanks for your great comment. Based on the current research, the only supplements Dr. Greger recommends are vitamin B12, Vitamin D, and possibly an Omega 3. Here are links to videos discussing each of them:

      He also has a great video on plant based diets for improving mood:

      Hope you enjoy those videos.
      Kelly Moderator

  12. Hi Kelly,
    Thanks for mentioning this videos mainly plant-based diets for improving mood. Also, many thanks to Dr Gregor for this article about hydration and its importance. It is a high time for drinking water!

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