We’ve heard it for years: “you need to drink at least eight glasses of water a day”. But is this actually true – do we need this much water every day? You only need to walk down the street and see the number of people carrying water bottles to know that water (particularly bottled water – but that’s another story) has become a big part of our lives. Many people have become “aquaholics” and it has almost become part of our daily checklist to ensure we have a full bottle of water to take out of the house with us.
In reality, 8 glasses of water equates to approximately 2 litres of fluid per day. Water is present in many other forms and foods than just tap or bottle water. Water is in fruit and vegetables and many of the other foods we eat. It’s in tea and coffee, alcohol, juices. So the reality is – you do not have to consume all the water you need through drinks.
It is possible that the “8 glasses of water a day” advice stems back to 1945, when the US Food and Nutrition Board of the National Research Council wrote: “A suitable allowance for adults is 2.5 litres daily in most instances. Most of this quantity is contained in prepared foods”. So, as mentioned above, a fair component of the water you need may already be there in the food you eat. It seems that this last important sentence: “Most of this quantity is contained in prepared foods” just got ignored.
Studies show we can potentially get up to 1 litre of water a day from our foods (4 cups worth). Your body produces another 250 mls (1 cup) of water a day as it metabolises fats, proteins and starches within the body. So using the above recommendation, you may really only need an additional 4 cups of water a day to satisfy the above recommendation. Even tea, coffee, milk and juices have fluid content that counts in this additional 4 cups worth – it doesn’t have to be solely plain water! The only issue with caffeine based products is you also need to be aware of the diuretic (water loss) effect that they can have.
So it seems that there is no magic threshold of water consumption that we need to strive for each day. So the question really becomes “Are we healthier if we drink more water”. There is no doubt that replacing carbonated, sugar filled soft drinks with water would be a much healthier option, but unfortunately scientific studies have failed to find any evidence that simply drinking more water results in better health outcomes.
What about drinking water to stave off dehydration? Do we need a recommendation to ensure we don’t drink too little water? The human body is an amazing structure, and it is finely tuned to signal you to drink long before you’re actually dehydrated. So listen to those little signals from your body – that feeling of thirst will tell you when fluid is required. This doesn’t mean you should wait until you are thirsty to drink – it just means that if you really require fluids because of low intake, your body will signal you before you enter the real dehydration phases.
And don’t forget that besides thirst, the body has another inbuilt mechanism which helps us determine the hydration status of our body– your urine colour! Ideally your urine will be a very pale yellow, but if it is showing a stronger yellow tinge, you are probably best to increase your fluid intake in the short term. And if you are over-hydrating (which can be just as big a problem, as you will learn below) your urine will be almost clear and you may have to slow down your fluid intake, at least in the very short term.
Can You Drink Too Much Water?
Unfortunately the answer is yes, and there are quite a few cases of this in the literature. It is common in endurance events, hot conditions, or for conditions such as cramping, to recommend the intake of high volumes of water. However science now suggests that the effect of over-hydration is quite possibly more dangerous than dehydration!
Hyponatremia occurs when someone consumes so much water that his or her body can’t rid itself of the excess via the usual means of sweating or urination. As a result, water levels rise in the bloodstream and sodium and electrolyte levels become diluted and fall as a consequence. This electrolyte imbalance can cause irregular heartbeat, brain malfunction, seizures and even death. The process of osmosis tries to balance this inequality by drawing water out of the blood and into the surrounding body tissues, causing the cells of these tissues to swell significantly. In effect, this process drowns the cells of the body in fresh water. If this process occurs in the brain, the response can be lethal. Think of it like “water intoxication”.
Hyponatremia has long been associated with endurance events like the marathon but has been reported in sports such as triathlon. Thankfully hyponatremia is rare in the general population – it is more an excessive intake of fluids during these extreme endurance sporting events or harsh climatic conditions that pose the risk.
What is fascinating (from a medical perspective) is that many of the deaths that happen with trekkers on the famous Kokoda track occur in young, healthy, and fit individuals. And even more interesting is that the majority of the deaths and evacuations happen in the first few days of the trek (not the last few torturous days as you would expect). In 2009 alone, four previously well hikers died of supposed hyponatremia. The thought process here is that on arriving at Kokoda, trekkers are hit immediately with the harsh and humid conditions, and knowing that the first few days of the trek are amongst the toughest climbs, try to “get ahead” by hydrating excessively. In an environment where your electrolyte balance is critical, drinking too much can have devastating effect!
There are however cases in the literature of people drinking themselves to death – there are a variety of reasons: dares, mental illness, and the attempt to overcome heat illnesses being a few. In one such example in 2007, a mother-of-three entered a contest run in California by a radio station. The person who could drink the most water without going to the toilet would win a Nintendo Wii game console. She drank about 7.5 litres of water, suffered severe swelling of the brain and died. She drank in a few hours three times as much as she normally took in over a whole day.
Consider even these thoughts related to excessive fluid intake:
· Hyperhidrosis (excessive sweating) sufferers often drink excessive fluid to replace the large amount of fluid they lose through sweating. However research suggests that it may be the excessive fluid intake that causes the excessive sweating: a self-reinforcing cycle that begins with the fluid intake, not the fluid loss!
· Excessive fluid intake in the evening can disrupt sleep. Overnight, the body releases an anti-diuretic hormone (ADH) to slow kidney function and make the urge to urinate weaker. Larger volume fluids in the evening can over-ride the ADH, fill the bladder, and wake you with the urge to urinate.
In summary, there is no evidence based recommendation for a specific amount of water people require daily. Amounts can vary greatly depending on what people eat, where they live, their body size, physical activities etc. What we can take from the evidence is that obsessing about reaching some water goal every day has no scientific background. Most of us are going to satisfy our fluid intake requirements by having a healthy diet, drinking small amounts of fluid on a regular basis throughout the day, and listening to our body.
