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How Much Water Do We Really Need to Drink A Day??

It is finally Spring!  Spring has sprung and the sun is out.  People are off to work and off for the weekend with water bottles in hand, tucked into bags, and stacked ominously across their desks to ‘remind’ them to drink water.  For many years, we have been bombarded with the notion that we need to drink at least 8 glasses of water a day – that this is the lowest common denominator one must meet in order to be healthy, and if you exercise, you need even more!  Whenever I ask someone about diet and fluid intake, they always start by shaming themselves ‘I drink coffee and tea – but I don’t drink nearly enough water…’.  Guilt abounds – and entirely unnecessarily. People are worried about how much water is needed to live far more than they should be.

The details on how much we supposedly ‘need’ to drink varies – but the core ‘wisdom’ is the same.  Drink water.  Lots of it. Nothing else counts, either, apparently.  Every healthy living magazine, newspaper and website seems to reinforce this ‘drink water’ message and so it may come as a big surprise to learn that this is one of the biggest health myths around. Everyone has an ‘opinion’ about how much water we need to drink a day.

Water is certainly important.  However, it is a non sequitur to say that because we are made up of a lot of water we must therefore drink a lot of it.  There is no evidence to support this idea.

Where did this idea come from?

The first record of a recommendation was an obscure statement in a document written by the National Research Council in the US in 1945 that said that 1ml for each calorie of food was a good amount of water – but that most is contained in the foods we eat.

The earliest ‘popular’ reference to this recommendation for water was in a newspaper obituary. A leading US nutritionist by the name of Frederick Stare died in 2002 and his obituary said that he was famous for suggesting people drink six glasses of water a day.  In his book, written in 1974, he did suggest drinking 6-8 glasses of water but that water is very well regulated in the body and that fruits and vegetables were good prime sources, as were coffee, tea, etc.   He wrote those two sentences about water at the very end of his long text – almost an afterthought.

He was clear that healthy food sources were the key and were adequate but somehow this statement got spun into the media hype we continue to see that exhorts us all to drink 8 glasses/day.  It has spawned everything from a list of experts saying you must drink X oz, competing with those who say Y oz and several iterations of ‘organic water’, ‘vitamin supplemented water’ and the like. There was no evidence to support his statement back then – and there is still no sound support for the idea now.

Other supposed ‘benefits’ of drinking water

Here are a couple of the more common ‘uses’ for drinking water:

Weight loss: people suggest drinking water during a meal promotes feeling full.  There is limited evidence to support this and none to suggest how it reduces appetite or how much water would be needed. There has been research done that shows that foods made with water (ie a soup) are more satiety provoking than the equivalent food (minus the water – ie a casserole) plus water drunk alongside during the meal.  So it can’t be the water doing it – but the ‘common sense’ that filling up on water is so pervasive that this strategy is routinely ‘prescribed’ when helping people manage meal sizes.

Constipation: high fluid intake is sometimes ‘prescribed’ to reduce stool density.  The large intestine has a massive capacity for absorbing excess water (because it is so important, our bodies are great at getting it!) – so it doesn’t have an effect on stool volume in healthy people.  There aren’t any good studies on whether water intake affects stool density in those who have constipation. Again, the ‘common sense’ has no evidence and possibly runs counter to what we know about physiology.

It is like the idea of ‘healthy’ includes drinking lots of water…which handily also means that it somehow is OK to eat inadequate food or not learn good nutrition strategies if one has an issue with weight control. I can understand why people want to feel they are ‘doing something’ for themselves – I really do – but I think there are more potent strategies to improving health

Toxins’:  Lots of water supposedly helps our kidneys flush out “toxins” (whatever they are). Ironically, large amounts of water actually reduce our kidney’s efficiency at filtering out our naturally produced ‘toxins’. (Can you tell I don’t like that word?)  Dr Goldfarb, a kidney expert at the University of Pennsylvania, said: “In fact, drinking a large quantity of water surprisingly tends to reduce the kidney’s ability to function as a filter. While it may be a subtle decline, it is definite.”

Why Drinking Water in Large Quantities is Not Needed

Our bodies are extremely efficient.  We don’t need our conscious attention to ‘hydration’ in order to function unless we have certain illnesses, travel in hot areas, or exercise vigorously.

Water distributes key chemicals and transport for food and other nutrient needs.   Water is certainly the most vital requirement for human life.  Indeed, many of these metabolic reactions also CREATE water – precisely because it is so important.

If someone is healthy, they really only need to concern themselves with increasing their water intake after they have exercised or during the times when they are in hot climates. Eating a good diet goes a long way. Other beverages we drink are more than sufficient to meet our water needs.

When Do We Need To Drink More?

The American College of Sports Medicine recommends that athletes drink 16 ounces of fluids a couple of hours before starting sports practice.  A stroll in the park or sitting at a desk doesn’t count.

The Dehydration Myth

Especially for those who are active, it is important to know the symptoms of dehydration.  For mild to moderate dehydration, the symptoms are dry mouth, eyes and lips, headache, tiredness and a decreased urine output.

Severe dehydration symptoms include extreme thirst, very dry mucous membranes (eyes, lips, mouth, genitals), passing a very small amount of dark urine, and a lack of sweating.

In healthy adults thirst is triggered by an increase in our blood osmolality (the ‘concentration’ of our blood products – caused by a reduction in fluid) – this thirst response happens when our blood concentrations have increased by two percent (or in other words, our fluid component of blood has been reduced so that we have two percent more blood proteins than we should).  Clinical dehydration sets in when that concentration of proteins has increased by five percent.

So you’ll be thirsty long before you are dehydrated – drink when you’re thirsty and you will be fine.

It is also a myth that coffee, tea etc dehydrates you.  You get a tiny bit less water out of that 6 oz mug than if it were pure water – but the net balance is still that you get more water than you had before.  Despite what you hear, coffee and teas won’t magically suck water out of your body and leave you worse off.

Can You Drink Too Much?

Yes.  Drinking excessive amounts of water can cause hyponatremia, an abnormally low level of sodium in the body.  Lots of water at once can also cause the kidneys to falter and cause a drop in blood sodium.  The problem is that a drop in sodium can cause the brain to swell.

People who live in hot climates or are actively exercising might be so thirsty that they drink water in dangerous quantities.  Drink to thirst.  That is the guideline supported by the evidence.

Sources of Water in Food

Getting water from these natural (and nutrient filled) food sources can go a long way in helping you intake a suitable amount of water each day.
Have a look at the water content in these foods:

– Apples (100g): 84.5g

– Broccoli (85g): 77.45g

– Cucumber (150g): 112.2g

– (Raw) Chicken Breast (125g): 94g

– Grapes (100g): 81.8g

– Sweet corn (85g): 59.5g

The bottom line is that if you are an average person in the UK climate you probably do not need to drink extra water. Drink whatever you drink and don’t fret. Ask your healthcare professional about your water intake needs if you are on any medications that may affect your kidney, liver or brain, or consult an appropriate professional if you are a very active athlete or travel extensively in different climates.

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