The British Medical Journal (BMJ) is a publication full to the brim with learned and generally quite turgid scientific research and reports. Except, that is, for the Christmas edition, when the editors attempt to ‘lighten up’ this publication a bit with the inclusion of more quirky and seasonal items that would not necessarily make it through the peer review process or be deemed fit for an academic journal.
This year’s Christmas edition contains an item on medical ‘myths’ that caught my eye [1]. The authors of this article attempt to expose a number of erroneous beliefs including the notion that mobile phones can disrupt medical equipment and that reading in dim light can increase the risk of short sightedness. But the supposed ‘myth’ that really captured my interest is one about the ‘need to drink at least 8 glasses of water a day’.
The authors of this article seem to base their opinion on a previously published study which claims to find no evidence to support the 8 glasses a day dictum [2]. However, I have not been able to find any research which has specifically tested the concept that drinking 8 glasses of what each day is beneficial compared to drinking less than this amount. So, there is simply is not enough ‘evidence’ to make the call one way or another. In the minds of some doctors or academics, it seems that absence of evidence means evidence of absence. But of course, that’s simply not necessarily the case. So, to call the concept that we should drink 8 glasses of water a day a ‘myth’ is simply incorrect.
In fact, the logic of dismissing the value of drinking 8 glasses of water a day in the absence of evidence to the contrary is similar to concluding that smashing your face with a polo mallet causes pain and injury’ is a ‘myth’, on the basis that there are no studies in which individuals have been smashed in the face with a polo mallet.
My overwhelming experience in practice is that when individuals drink water regularly throughout the day, they feel better (both mentally and physically). While there is not much research on the benefits of hydration, there is quite a lot on the hazards of dehydration. For instance, some research has linked dehydration with reduced brain function [3,4]. Also, the research suggests that as little as 1 per cent (of body weight) dehydration can make a difference. This equates a deficit of only 700 mls for a 70 kg person (about 24 fluid ounces for a 154 lb individual). In a previous piece that I’ve pasted below, I also highlight some of the evidence which links higher levels of water consumption with a reduced risk of heart disease and some forms of cancer.
So, while we don’t have research which supports the ’8 glasses of water a day’ recommendation, we don’t have any evidence to disprove it either. On the other hand, we do have quite a depth of research which shows that even mild levels of dehydration can have adverse effects on wellbeing, and that higher levels of water consumption are associated with a reduced risk of disease. Taken as a whole, one wonders what the objection there is to advising individuals to drink 8 glasses of water a day.
Well, the authors of the BMJ article conclude their piece on water with these ominous words: �drinking excess amounts of water can be dangerous, resulting in water intoxication, hyponatraemia, and even death�. That’s right, they leave us with the thought that drinking too much water can kill us. Of course they neglect to tell us that the volumes of water required here are way, way higher than individuals could comfortably manage in their everyday lives. Oh, and they fail to cite any evidence for the hazards of water either. So, apparently a lack of cited evidence is fine if you want to warn of the mortal dangers of hazards, but a similar lack of evidence is not OK when considering the potential benefits of water.
At the time of writing I notice that electronically submitted ‘rapid responses’ to the BMJ article point out that the evidence suggests that the authors are wrong on mobile phones and medical equipment and reading in dim light and short-sightedness. I reckon the authors have got it hopeless wrong on the value of water too.
As I pointed out last week, water drinking can have particular benefits at this time of year because it can help temper our alcohol intake quite naturally. Whatever some may contend, my advice is still to get plenty of this most fundamental of fluids down you.
References:
1. Vreeman RC, et al. Medical myths. BMJ 2007;335:1288-1289
2. Valtin H. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8″?Am J Physiol Regul Integr Comp Physiol. 2002;283(5):R993-1004.Click here to read Links
3. Grandjean AC, et al. Dehydration and cognitive performance. J Am Coll Nutr 2007;25(5):549S-554S
4. Lieberman HR. Hydration and cognition: a critical review and recommendations for future research. J Am Coll Nutr 2007;25(5):555S-561S
The value of water – 15th December 2002
The importance of keeping the body well-hydrated is a common theme in natural health circles, and we are often advised to ensure eight glasses or so of water passes our lips each day. However, while there is often much talk of the need to supply the body with plenty of water, it occurs to me that there is often little explanation as to why. For all this enthusiasm for water, it’s amazing how aqua advocates tend to dry up when pushed as to what water’s benefits actually are. This week, I thought I’d see what evidence there is for water’s fabled effects in the body. A closer look at the science reveals that water has a bucketful of benefits
The body is 70 per cent water, a fact which means that might make us stop and think that water does something useful in the body. Water is essentially everywhere in the body, and therefore participates in all the physiological and biochemical processes that are essential to life. From nerve impulses that travel from the brain to the body, to the transport of oxygen and nutrients around the system, water plays a starring role. This throws up the possibility that when the body is low on fluid, nothing works quite as well. From a theoretical standpoint at least, water is an important component in the maintenance of optimum health and well-being.
Increasing our water consumption not only helps to maintain general well-being, there’s also good evidence to suggest that it can protect us from certain illnesses too. Scientific studies show that drinking more water helps protect against kidney stones. Other research suggests that water might protect against heavyweight conditions such as cancer too. One study found that drinking plenty of water was associated with protection from cancer of the bladder. In another study, women consuming five or more glasses of water per day have about half the risk of developing cancer of the colon compared to women consuming two or fewer glasses of water per day.
Other evidence suggests that drinking more water might protect against heart disease too. A study published earlier this year in the American Journal of Epidemiology looked at the effect of differing water intakes on the risk of dying from a heart attack. In women, higher water consumption reduced risk of dying from a heart attack by 40 per cent, and the risk in men was cut by more than half.
Some people use thirst as a sign that they need to drink more. By the time we are thirsty, the body can be as much as 2 per cent dehydrated. However, even at only 1 per cent dehydration we may already be feeling the effects, relying on thirst to tell us when to drink quite simply is not good enough. Probably the best way to monitor our need for water is to keep a check on the colour of our pee. Essentially, the paler in colour our urine, the better our state of hydration. Our aim is to keep our urine colour very pale yellow or pale yellow throughout the day. If our urine colour strays into darker tones, particularly if it starts to whiff a bit, then it’s time to reach for the water.
The essential key to getting 2 litres of water into the body each day is this – keep it by you. Water is something we may not seek out, so it makes sense to keep it readily to hand. If you’re doing the gardening or you’re in the gym, keep a bottle of water with you. Put a bottle of water on your desk at work. Keep a jug of water and a glass on the kitchen table. Take a bottle of water in the car and carry one in your handbag when you are out and about. Keeping water by you is likely to ensure you get your daily quota without even thinking about it.
Yes I saw this article and doubted the veracity of the so-called myth debunking too. It would just suit the government if everyone believed that it was okay to read in dim lights, in view of the upcoming European legislation on light bulbs.
I think what they were trying to say with the water was that it was an arbitrary amount based on a suggestion that we should drink eight cups of water – presumably the American measure of a ‘cup’ (whatever that is). But they should suggest a less random amount, based on size perhaps, and emphasise the importance of drinking plenty of water, rather than telling us the minimum amount necessary for survival. Survival isn’t the sum of health. Wow, I wonder if there are plans for water rationing! (I jest – I hope!)
Surely they didn’t say don’t drink water, but that there are multiple sources of fluid, & to prescribe that everyone should drink 8 glasses of water on top of everything else (how big is a glass?) has no evidence base. The point being that the 8 is often quoted as if being based on hard evidence. At one point you mention monitoring your pee & I would have thought that frequency of peeing plus a colour check would be better advice.
How have we all survived without having 2 litres bottles of water with us all day?
Pete
The point is that with no evidence (except anecdotal, of course) one way or the other, then the 8 glasses of water a day recommendation cannot really be called a ‘myth’, can it?
Frequency of urination might be useful indicator or state of hydration, but with considerable variance in bladder size it becomes almost impossible to give broad recommendations here.
We may have survived with less water than is typically advocated, but what is enough to survive and what is optimal might be two very different things.