The overlooked danger of overhydration

I grew up in Sri Lanka, a tropical country where it was pretty hot during the day and we perspired a lot. But we did not pay too much attention to staying hydrated by drinking water all the time. Furthermore, in middle class homes like mine, there was the belief that tap water was not pure enough to drink and could contain dangerous bacteria and so in our home water was first boiled and then cooled in the refrigerator. We did not drink water outside the home unless we were in another middle-class home that followed the same practice. We drank water with meals and two or three cups of tea and/or coffee during the day. As younger schoolboys we would take a little canteen of water with us to school but as we got older, we stopped doing that and simply did not drink water until we got home. If we got thirsty drank hot tea or coffee or bought a bottled drink, bottled water not being a thing then. When we played sports as children during the blazing hot days, we would of course get thirsty and would drink water when we felt the need.

It was only after coming to the US that I saw people do ‘preventive drinking’ of water, also known as ‘staying hydrated’ and then later people started carrying around water bottles with them and made it a point to drink from it regularly, even though they were living in a mild climate and were not exerting themselves. The fear of becoming dehydrated had become pervasive and Tamara Hew-Butler, a professor of exercise and sports studies at Wayne State University (academic departments are becoming so specialized these days!) warns that people, especially those in charge of sports programs for young people and athletes, are carrying this too far and ignoring the opposite, but very real, danger of ‘overhydration’ that can lead to hyponatremia and even result in fatality. She recommends that people should return to the practice that I followed as a boy and still follow as an adult, and drink when they get thirsty.

Turns out, the neuroendocrine thirst circuit dates back 700 million years and is found in most animals, including bugs and worms. Thirst activates the same conscious area of the brain that tells us we’re hungry or have to pee. To say we need to stay “ahead of thirst” (or die) is like saying we need to pee every hour to stay ahead of imminent bladder explosion (or die). The molecular and neural circuits that govern fluid intake (and micturition) in real-time are absolutely exquisite.

It’s remarkable to think that animals survive without water bottles and urine charts – they drink when they are thirsty, and we should too.

Hyponatremia is caused by drinking too much water or sports drinks, which dilutes blood salt levels below the normal range. Any sudden drop in blood salt levels, from drinking more than the body can excrete, can cause all cells in the body to swell. Brain swelling from hyponatremia can cause headaches and vomiting, while muscle cell swelling can trigger whole-body muscle cramping.

What is most frightening, however, is that these symptoms mimic those of dehydration They are often treated by medical staff with more fluids.

Drinking when you are thirsty is not “too late,” because the thirst mechanism is hardwired into the nervous system to protect against scarcity.

Then, what about the need for eight glasses of water per day? There is no evidence to support this. What about peeing until our urine is clear? Dark colored urine merely reflects water conservation by the kidney, rather than water lack by the body.

She points out that we should not ignore, of course, the pernicious influence of the bottled water industry that has persuaded people that tap water in the US is not as good as their product and also urged us to drink a lot of it.

We should recognize who the “true champions” may be with regards to most modern day hydration advice. According to the latest figures, bottled water sales have increased to US$18.5 billion dollars, up 8.8 percent from the previous year. This revenue does not include the vast array of purified, infused, oxygenized, sparkled, distilled, intravenous and reverse osmosis versions that compete for attention on the market.

In addition to being a waste of money, it causes a huge amount of plastic pollution and depletes the ground water resources of many communities.

At one point, I too bought into the now-discredited idea that we must drink eight glasses of water a day and that drinks like juices and coffee and tea should not count towards this total. But I just could not keep it up. It made me feel bloated and uncomfortable and require going to the bathroom frequently, which was a nuisance. So I reverted to my earlier behavior. I know pretty much exactly how much fluid I drink a day: One cup of coffee with my breakfast, one cup of tea in the late afternoon, and a glass of water with lunch and again with dinner, with an extra glass thrown in now and then on days when I feel thirsty. This is only about half the purported requirement. Of course, I lead a very sedentary life. And people vary in their needs. Other people may well need more fluids, especially those who exert themselves a lot or are in extreme and unusual situations,. But for most people, drinking when you get thirsty seems to be the recommended policy.

The advice to practice moderation seems very applicable here.


  1. Rob Grigjanis says

    Yeah, I never bought the eight glasses a day stuff. Thirsty; drink. I’m at home most of the time, and always have a glass of water handy. Not sure how many glasses I have a day, but I’d guess it’s between two and three. And three cups of tea or coffee. When working out, I feel the need to drink a few mouthfuls after about 20 minutes, then at the end.

    And I’ve always hated the idea of ridiculously priced bottled water. For a few days supply in case of emergency, I keep 12 bottles of 1.14 litre vodka bottles filled with tap water, replacing the oldest when I’ve finished another bottle.

  2. jrkrideau says

    The only time I consciously make myself drink is on long bike rides in hot weather. On one 180km ride on a very hot day, I probably went through close to 10 litres of water and sports drinks. We lost one rider due to dehydration but she was fine in 3 or 4 hours after a quick visit to the hospital emerg.

    The eight glasses of water rule has always seemed suspicious.

  3. Andrew Dalke says

    Snopes says the ‘eight glasses of water each day’ may come from 1945 when “the Food and Nutrition Board of the National Research Council stated that adults should take in about 2.5 liters of water per day (which is roughly the equivalent of eight glasses of water), but it also noted most of that intake level was already satisfied through the consumption of food without the need for the additional drinking of water.” --

  4. Matt G says

    When too many would-be frat members started dying from drinking too much alcohol as part of their hazing rituals, some switched to water. What physiologists call water intoxication was fatal in some cases. My understanding is, however, they you have to try pretty hard to OD on water. Overeating can be painful, so can overdrinking….

  5. mnb0 says

    Ironically exactly you should be careful during heatwaves, MS. Every year in summer elderly people in Europe die of dehydration because they don’t drink enough -- they don’t get thirsty anymore.

  6. says

    Part of this may be a trickle-down effect (excuse the pun) from competitive endurance athletics, in particular, distance running (of which I was a part). By the 1990s it was well known that even modest fluid loss would impact performance so distance runners, especially at the half and full marathon distances, would make sure to stay hydrated. Indeed, people often came up with their own concoctions, adding small amounts of sugar and salt to replenish glycogen and balance electrolytes. The CHO concentrations are typically half to one-third of soda or fruit drinks (this is what you find in most sports drinks). The earliest work that I know on this was purely empirical self-study by a famed British distance runner some 100 years ago (I think Arthur Newton, but I could be wrong). He recommended a mixture of weak lemonade with a pinch of salt and perhaps some sodium bicarbonate. It should be noted that at the full marathon distance, additional CHO is pretty much mandatory for best performance.

    Exercise physiologists had this pretty well figured out 30 or 40 years ago and it began to make its way into the popular press to feed the second running boom that grew throughout the 1990s and early 2000s. No issue of Runner’s World or Running Times would be complete without at least one article on the subject. The thing that was ignored is that performance reductions typically become noticeable after 60 minutes of competition. As far as glycogen depletion is concerned, that will take even longer assuming competitors are following healthy diets (ie, not Atkins). Of course, this is all predicated on people competing at very high levels (at least of their own maximum performance).

    The end result is that no one needs to carry water/sports drink for the local 5k or even 10k. After years of competing, I would not consider taking water unless my expected finish time was over an hour. For me, that meant half-marathons and longer. I might bring along a gel (100 kcal of CHO) if I went on a long training run (18+ miles), but the idea of carbo-loading for a 5k or 5 mile road race is nothing but ridiculous. On more than one occasion I passed a competitor who slowed at a water stop and stayed ahead (slowing always messes with your stride).

    The end result is that casual runners and other endurance sports enthusiasts hear about this, but only hear part of it. Add to that the organizers wanting to make sure that no one passes out from heat/dehydration (and possible legal action). Finally, you get the “if athletes do it, then it must be healthy, therefore if I do it I will be healthier” mindset* and you get the current phenomenon.

    *I will always remember checking out at the local grocery store and seeing two 40-ish guys in less than stellar physical condition in front of me with a pile of chips, soda and the like. At the last moment, one of the guys added a PowerBar. Seriously, stop kidding yourself and just grab the Snickers that you really want. A PowerBar is not health food. It’s an effectively marketed shelf stable food substitute that the vast majority of people have no use for (I used to use them after particularly long workouts where I could not get to real food quickly- the things would stay edible after conditions that would turn a banana into mush, like a couple of hours in a car in the summer sun).

  7. stumble says

    There are good reasons to drink before you feel thirsty, but they primarily relate to people involved in very strenuous activity for long periods of time. It can take up to 2 hours for water to be absorbed, and if you haven’t pre-loaded the system you absolutely can end up dehydrated by waiting until you are thirsty until you drink. But you will not hit this point unless your body is burning thru a lot of water thru activity.

    During my time in the military, during long hikes (carrying 75lbs of gear) for instance, it was not uncommon for people to end up dehydrated because they hadn’t consumed water prior to stepping off. But this is a harsh physical activities that would take six hours or more. The same for long duration sports outside during the summer… The lag time between consuming water and it being absorbed for most people under most circumstances is meaningless, but for duration athletics it can be critical.

    This is just one more example of data from a specialized source not being applicable outside that arena. Runners are generally recommended to replace their shoes every two months because the padding wears out. But for someone who isn’t running 50 miles a week that would be ridiculous.

  8. says

    Not too much water, not too little. Also don’t forget electrolytes, magnesium tablets are useful on hot days. Also see a sports doctor if in doubt, not some random quack off the internet.

  9. anat says

    Dehydration is less of a problem in a tropical climate than in a dry one. In a dry climate you can easily lose a lot of water by perspiration without noticing. Also, it is not that hard to train oneself to ignore the sensation of thirst or to misinterpret thirst as ‘feeling like wanting a snack’ (not actual hunger). As a result I was often low on hydration in the summers during my teens -- dark urine, wooziness.

  10. says

    When I briefly worked putting on commercial roofing I would take a gallon of water with me (it was just tap water). I would try to remember to put it in the freezer the night before. I don’t think I made any effort to force myself to drink it, though (and yes, I drank it all). Other than that, I really don’t ever take water with me.

  11. says

    As a cyclist who regularly rides 50 to 80km on a Sunday, I carry enough water and food to stay comfortable. If I feel thirsty, tired or hungry, I stop for a break. It makes the day’s outing more enjoyable.

  12. says

    Also, it is not that hard to train oneself to ignore the sensation of thirst or to misinterpret thirst as ‘feeling like wanting a snack’ (not actual hunger).

    This. In middle school, our toilets were not nice, so I tried to avoid using them. Which meant that I didn’t drink for about 10 hours (left at 7 am, came home at 5 pm). By my late teens, I had completely lost the feeling of “thirst”. Often I would come home in the afternoon with a raging headache. Of course taking some medication helped, for like an hour. After a week of painkillers I realised that I’d fallen into the habit of drinking a cup of coffee in the morning, then nothing, and then the glass of water with the painkiller, which was what actually helped me.
    What I never felt was thirst.
    At that point I started to carry a water bottle. We have like a dozen sturdy plastic bottles that get used and used again, with water or cold herbal tea.
    And yeah, I remember my grandparents frequent bouts with dehydration. My grandma would start talking nonsense, at which point we sat her down and handed her a glass of water, and another one an hour later, after which she would stop talking nonsense.
    Another myth is that you can just “fill your depots”. Your body cannot deal with a litre of water at once. All it does is put an additional strain on your kidneys.

  13. mvdwege says

    What surprises me is that people tend to worry about hydration during sports, but never about also keeping their electrolytes up. There is a reason why you are advised to take salt pills during long endurance events.

    Me, being a low-salt eater (I just don’t like the taste, I prefer spices), am all too aware of what happens if you try to compensate for dehydration without taking salt. If I am at a martial arts event where I will spent long time in protective gear doing strenuous workouts, I can feel the difference if I take a bag of salted peanuts with me. Without something to keep my salt levels up, I start distinctly feeling unwell at the the end of the day, despite only drinking when I am thirsty.

    I have learned to listen to my body, and knowing I have low salt levels to start with I learned to recognise the difference between the very early onset of hyponatremia (it starts at a loss of concentration for me) and dehydration. But it helps that I know of the very existence of hyponatremia. Like Mano’s linked article points out, too many people don’t even know that much.

  14. jazzlet says

    There are people who need to be more careful about their fluid intake (not specifically plain water) for medical reasons. Mr Jazz only has one kidney as the other was removed after a tumour was found on it, he has been told by his urologist to keep his urine pale to avoid stressing the remaining kidney in any way, and in his case this means drinking two or occasionally up to three pints of tap water a day on top of what he gets from food and drinks. However this certainly doesn’t apply to people with two kidneys!

  15. Jenora Feuer says

    There’s also the infamous “Hold Your Wee for a Wii” contest in which a woman died of water intoxication. And in which the morning hosts dismissed the concerns of others that the contest was dangerous, including apparently a nurse who offered to supervise for free (that dismissal figuring significantly in the later lawsuits).

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