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The Science News

Are we waterlogged?

On the topic of water or fluid intake, the common wisdom is this:

Try to drink about six to eight glasses of water (or other fluids) a day to prevent dehydration.

Many schools also feel it appropriate to insist that pupils are accompanied to school by a water bottle.

Other organizations, often with conflicting interests, reinforce this wisdom. For example, Hydration for Health (created by French food giant Danone — makers of bottled waters including Volvic and Evian) recommends 1.5 to 2 litres of water daily as “the simplest and healthiest hydration advice you can give.” It also claims that “even mild dehydration plays a role in the development of various diseases.”

However, the scientific literature on the subject shows that there is no high quality published evidence to support these claims.

We can keep in mind several studies showing no clear evidence of benefit from drinking increased amounts of water and suggesting there may be unintended harms attached to an enforcement to drink more water.

Says Margaret McCartney in the newest British Medical Journal:

For instance, reports that increased water intake in children can improve concentration and mental performance have not been confirmed by research studies, while data relating water drinking to a reduction in children being overweight are prone to bias.

While there are some conditions that do benefit from drinking increased water, such as in people with recurrent kidney stones, other evidence for preventing disease is conflicting, adds McCartney. In other words, this is a complex situation not easily remedied by telling everyone to drink more.

Often, untangling the evidence presented by companies with vested interests like Danone proves difficult. McCartney says this “results in weak and biased selection of evidence,” she argues.

This myth additionally meets the classic criteria exhibited by many urban health legends: it warrants excess, it stresses public virtue, and it claims to be a “magic bullet”.

My Opinion

In this case, I think that your senses defeat the common wisdom: if you feel thirsty, drink, if you don’t, don’t.

Your body is a finely tuned machine that regulates itself via a complex process of homeostasis. This process regulates everything from hunger to heat, and makes sure that your metabolism stays steady. There are three important homeostatic mechanisms: osmoregulation, thermoregulation and regulation of blood sugar levels. Homeostasis is important because it results in our cells being bathed in tissue fluid which has the correct amount of water, mineral salts, glucose and temperature.

The specific mechanism for thirst however, is called Osmoregulation. Osmoregulation is the control of the levels of water and mineral salts in the blood.

Homeostasis in action

The jist of this is that your body is keenly “aware” of your body’s hydration level, and will make changes accordingly. Therefore, if you feel thirsty, you are probably somewhat hydrated, and you should drink. If you are not thirsty, you are most likely not dehydrated, and do not have to drink. Just guzzling water to make that “magic” 8 glasses a day has no shown benefit beyond hydration.

Your body is amazingly good at using the resources that it is given. Given that, it is not that hard to navigate the wide chasm that represents the two extremes: not shriveling up like a dried-up sponge, and not drowning yourself.

There is no evidence to show that increasing your intake of water beyond that of fulfilling your thirst is beneficial to your health, so relying on your body’s tried and true evolutionary mechanism of homeostasis is your best bet.


There is no rigorous evidence to show that you need eight glasses of water a day. Beyond hydrating you, increasing your water intake won’t cure disease or keep you focused, it will just make you pee more often. You should definitely be getting your fluids everyday, but base this on the signs of dehydration like dry-mouth, light-headedness, nausea, or thirst, instead of trying to meet some untested, unverified, arbitrary amount of water.

Of course, this is not what large companies like Evian will say, but remember, they are trying to sell you water.

Instead of relying on a for-profit company to tell you how much water to drink, how about putting some trust in a “thirst-gauge” millions of years in the making: your own body.

So if you’re thirsty, drink! It’s that simple.

Story Source:

The above story is reprinted from ScienceDaily with editorial adaptations by SBL from materials provided by BMJ-British Medical Journal, via EurekAlert!, a service of AAAS.

Journal Reference:

1. M. McCartney. Waterlogged? BMJ, 2011; 343 (jul12 2): d4280 DOI: 10.1136/bmj.d4280