Hydration – What is our body’s requirement for fluid?

Hydration – What is our body’s requirement for fluid?

When does hydration really become important? 

The summer is here and the sun is out, which means the parks, streets and roads are full of people outdoors getting active. The warm weather raises the issue of hydration, and how to hydrate your body appropriately on a daily basis and when exercising. It is well established that water is essential for life and optimal physical well-being. We are well accustomed to the message that most people need to drink more water and that dehydration has implications for our health, but do we need to be drinking more and what is our body’s requirement for fluid?

Fluid balance

Water is required for countless functions in our body. Some of the primary functions include the transport of nutrients to cells, control of body temperature and to facilitate the transit of toxins and waste products out of the body. Fluid is lost from the body through urine, respiration (breathing) and perspiration (sweating). If fluid losses exceed fluid intake, an imbalance occurs resulting in a signal being sent to the brain (i.e. thirst) that encourages us to drink. If we don’t consume fluids when this imbalance occurs, dehydration can develop. Dehydration can impair physical and mental function, which has implications in many walks of life, and therefore is best avoided through appropriate daily fluid intake.

Symptoms of dehydration

– Thirst
– Nausea
– Dry skin
– Poor concentration
– Fatigue and weakness
– Increased body temperature
– Muscle cramping

Fluid requirements

Daily fluid requirements can tend to be over-stated and over-hyped by the media and the ever-expanding number of bottled water and drinks companies. That’s not to say that regular fluid intake throughout the day is not essential – it certainly is. The point I want to make is that our body has a capacity to manage fluid balance better than we are sometimes led to believe. When we are in good physical health, a normal individual will become thirsty when they require fluids. It is a normal homeostatic response i.e. those responses that naturally keep the body’s function in check. By then drinking fluids, you will restore or maintain your fluid balance. It is true that if you have a sense of thirst, then you are likely to already be slightly dehydrated, but this is readily recovered in the space of a couple of hours. So with that in mind, you don’t need a water bottle in your hand every half hour of the day…

However, there is an important distinction when it comes to athletes or those who exercise regularly, as these people have much greater requirements for fluid due to significant fluid losses resulting from sweating and heavy breathing during exercise. Numerous studies have shown that athletic performance can be hindered by even a relatively mild dehydration, so athletes should not rely solely on thirst to monitor hydration. Instead, athletes must aim to maintain fluid balance before exercise, and limit the extent of dehydration during exercise in order to achieve optimal physical performance. For this reason, athletes must follow a strict hydration strategy to minimise the risk and effects of dehydration. Regularly checking your urine colour is a simple and effective means to track your hydration, particularity in the lead up to exercise.

Fluid requirements

A general fluid guideline for the average-sized person who is not involved in heavy physical labour or regular intense exercise would be approximately 2 to 2½ litres daily. Appropriate fluids for optimal daily hydration include water, milk tea, coffee (if you are a regular consumer) and fresh homemade juices. You may be surprised to know a couple of things. Firstly, all fluids contribute to daily intake – it doesn’t have to be pure water. Secondly, fresh, whole fruit and vegetables also contribute fluid to the body, but that’s assuming you eat a good amount of fresh fruit and vegetables! Fluid requirements will, of course, significantly increase if your work involves manual labour, if you have larger body mass, or if you are working in a warm, humid or air-conditioned environment.

An example of a typical intake providing enough fluid on a daily basis might be as follows:

– A large glass of water with breakfast 400 ml
– A mug of black tea 300 ml
– A pint of water with lunch 500 ml
– A mug of green tea in the afternoon 300 ml
– A glass of fresh vegetable juice 300 ml
– A pint of water with or after dinner 500 ml
– Total fluid intake 2.3 litres 

Fluid requirements for exercise

The guideline above is for someone who is not performing exercise on that day. As I have already mentioned, if you regularly exercise your fluid requirements are much higher – probably about 1 litre extra per hour of exercise, and more if exercising in the heat. If you are preparing for a race, competition or if you are simple going to complete a high intensity training session you should follow a hydration protocol as illustrated below.

Optimal hydration protocol*
  1. 500 ml the evening before the event (two hours before you go to bed)
  2. 500 ml of water with breakfast
  3. 500 mL of water every two hours leading up to your training or event.
  4. This may be a little more depending on environmental conditions, or if you urine colour is not a clear/straw colour each time you pass water.
  5. Sip on 300 ml of fluid as you warm up
  6. Consume 2-3 mouthfuls of fluid every 10-15 minutes
  7. After exercise, replace fluid lost until thirst is satisfied and urine is a straw / straw colour.
  8. A good rule of thumb is to consume 1.5 litres of fluid for every 1 kg lost in body mass if you have the opportunity to weight yourself before and after your training or event.

* This is a general recommendation. Fluid requirements may vary depending on body size, level of hydration and environmental conditions

I don’t like water!

I regularly get the question: “I don’t like drinking water, so can I drink juice or add something to sweeten?” In short, we don’t recommend the vast majority of commercially-available fruit juices or juice-based drinks. Exceptions to this rule would be if they are freshly-made, or are being used to add carbohydrates to the diet in the lead-up to or after exercise. If you don’t like the taste of water alone, you can flavour water using slices of fresh fruit like oranges, lemons and berries. Cooling water with ice is always a good way of making it more palatable and refreshing, especially in the summer months.

Adding a pinch (roughly 1/8th of a teaspoon) of salt to the drink is a good way of improving the absorption of fluid and offsetting sweat losses. It is also an alternative to buying a sugar-sweetened and flavour-enhanced sports drink.

There is no doubt that water is a vital component of your diet. Regular fluid intake is essential for optimal physical function and should be implemented in your daily habits, but what this means in practical terms is a lot simpler than you might believe. Satisfying your thirst with water is common sense, but drinking a large glass of water on the hour, every hour, (or perpetually carrying a large bottle of water) leading to the numerous consequent toilet trips is not!