Water Is Virtually a Magic Substance – So Why Are We Drinking so Little Of It?
Wouldn’t it be amazing if there were a liquid you could drink that was refreshing, had zero calories, actually helped people to lose weight, and made your body work more efficiently? Better still if it came out of a tap and was piped to every house in the country!
Yes, you’ve guessed – this life-enhancing, health promoting, and entirely harmless drink is water.
Everyone knows – well, more or less everyone – that we’re largely composed of water. The figures tell their own story. Up to around 30 litres inside our trillions of tiny cells, up to about 13 litres in the gaps around the cells, perhaps 3.5 litres in our blood.
Given that you’re losing up to 1.5 litres in your urine each day, breathing out almost half a litre and sweating out up to 200mls a day (not to mention the up to 200ml in your poop, but let’s not go there!) you need to drink between 1.5 and 2.5 litres a day just to keep from drying out into a desiccated shell and being blown away on the wind.
If you lose enough water – perhaps a long run, or a sweaty session in the gym – a part of your brain called the hypothalamus will pick up on it and create the sensation of thirst. It will also, by the way, tell your pituitary gland to produce a chemical signal – anti-diuretic hormone – which will cause your kidneys to retain more water. But, once you’ve drunk anything watery, your blood volume will increase and become more dilute and your hypothalamus will ease off on its signals of thirst.
This is the normal mechanism, but it doesn’t tell the bigger and very important story.
For a start not all drinks are made the same. Sweetened drinks do contain water of course, but they come heavily laden with unhealthy sugar. More on sugary drinks another time, but suffice to say that they lie at the heart of the epidemic of obesity and overweight – and the diseases it causes – affecting all age-groups, including students at UK universities.
It’s often said that coffee in particular, and tea as well, are diuretic – they make you pee – but their hydrating effect far outweighs any increase in time on or around the toilet. So, tea and coffee without sugar – and that’s the critical thing – is a good way of taking in water.
So how many mugs-full of water (or unsweetened tea or coffee) should you drink every day? Most people get about a fifth of their water in food, and a general rule about the remainder is that men should drink about three litres, or twelve cups, and women just over two litres, or nine cups, a day in drinks.
Most people are not drinking enough water to optimize their health, or the way their bodies function. A study by the Centers for Disease Control and Prevention in the United States found that almost half of American adults were drinking less than four cups of water a day. Most of them were actually drinking three cups or less, and 7% weren’t having any at all.
Another interesting finding was that the driest Americans were also eating more fast food, fewer fruits and vegetables and exercising less than the recommended amount.
A study of many different research papers about inadequate intake of water, by Professor Ana Adan, found that a shortfall of just 2% in hydration causes a drop in performance in tasks requiring attention or psychomotor skills. It also impairs very short-term memory recall and can be noticeable in the way you feel.
Professor Adan says that people in early adulthood – such as students – are not immune. In the summary of her paper, she says, “No matter how mild, dehydration is not a desirable condition because there is an imbalance in the homeostatic function of the internal environment. This can adversely affect cognitive performance, not only in groups more vulnerable to dehydration, such as children and the elderly, but also in young adults.”
“Homeostatic function of the internal environment” is what the hypothalamus is doing, when it samples the concentration and amount of your blood and signals thirst to you and the need to conserve water to your kidneys.
It’s not only “cognitive” – or mental – performance that can suffer. Water plays a big part in healthy digestion, with the upper part of your gut adding a considerable volume of liquid to what you’ve eaten, the better to extract what you need from your food. The water is largely reabsorbed lower down.
Sufficient water is important for excretion of waste products, it helps to lubricate and buffer your joints, and it helps promote a healthy skin. Not drinking enough can lead to headaches, and constipation is one of the first things you might notice if your water consumption is below par.
Drinking more can also help you to lose weight. A study by Jodi Stookley of the Children’s Hospital in Oakland, California, found that over the short term at least, higher intake could reduce the amount of energy people took in and perhaps alter the way they burned their food as well. If the water’s cold your body will use energy heating it up. Remember that a calorie is defined as the energy needed to raise the temperature of one gram of water by one degree centigrade.
Consuming enough water is particularly important if you play sport, or simply go running or to the gym to keep fit. Dehydration diminishes your performance, and your ability to regulate your temperature. If dehydration gets out of hand you could have a dangerous drop in blood pressure, kidney failure or even seizures. But that’s rare – what we’re talking about in most people is the need to top up to optimize health and how you function, both physically and mentally.
As people get older their sense of thirst becomes more muted, and the risk of dehydration increases. But some experts say that in general people can rely for signals to drink on their hypothalamuses and the complex system measuring how dilute the blood is, and the concentration of water in and around the body’s cells.
There are also dangers of drinking too much. Excessive water in comparison to the salt being taken into the body can cause a dilution of sodium in the blood, affecting the vital functioning of this mineral. Signs of this condition – hyponatremia – include nausea, headache, fatigue and confusion. Although hyponatremia is rare, people have died as a result of it.
Just a note about salt – another topic we might return to. Salt absorbed from food and into the bloodstream (it’s typically sodium chloride, but you’ll see references to high or low “sodium”) will draw water in by a process of osmosis. That will make you thirsty and more in need of water just by itself. Excessive salt intake is best avoided, and when it makes you drink extra water, you’re just catching up, not necessarily achieving optimal hydration.
So, select a mug, find a tea-bag or the coffee pot, and put the kettle on!
- Adan A. Cognitive performance and dehydration. J Am Coll Nutr. 2012 Apr;31(2):71-8.
- Stookley, J.D., Constant, F., Popkin, B.M., and Gardner, C.D. (2008). Drinking Water Is Associated With Weight Loss in Overweight Dieting Women Independent of Diet and Activity. Obesity, 16, 2481– 2488.
