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A new paradigm has been presented regarding the function and role of water in human biochemistry. It is now generally believed that it is the water in our bodies that regulates all functions of the body, including the activity of all the solutes that are dissolved in it.

This is contrary to the previously held belief that the solute composition is the governing factor of all biological functions of the body, i.e. the water is just the packing material. Life on earth could not exist without its unique physical, chemical and electrical qualities. Why then if water covers 70% of the planet and makes up 70% of our bodies, is chronic dehydration pandemic? Perhaps it is due to its abundance that we take it so much for granted.

The most elaborate dietary regimes and costly nutritional supplementation can only work if a person is well hydrated.

When you become dehydrated a cascade of chemical events take place. Your body naturally begins to increase production of histamine. Histamine is present in all body tissues and produced by the mast cells found in connective tissue. Not only is histamine a mediator in inflammation, but it acts as a neurotransmitter, directing and operating the subordinate systems that promote water distribution to various tissues and organs. These subordinate systems involve the action of the hormones vasopressin and renin-angiotensin, as well as prostaglandins and kinins. When levels become excessively active the mucus membranes of the lungs, for example, can become irritated and in time the muscles and tissues that make up the breathing mechanism can go into spasm, resulting in severe breathing problems and at worse asthma . This in addition to long term damage to the immune system is bad news indeed for the athlete.

When the core temperature rises while training the blood that would otherwise be available for the muscles is used for cooling via respiration and perspiration. The body will do this automatically as temperature moves out of the preferred narrow range. It is this loss of water that ultimately impairs physical performance and interferes with normal cognitive function. Intense exercise can increase heat production in muscles 20 fold. Don't be fooled by lack of thirst and not feeling thirsty. These sensors are inhibited by strenuous exercise.

Fluid replacement is a much misunderstood and frequently misguided aspect of nutrition and performance. Here are some guidelines:

Prehydrate – By drinking extra water for the 2 days preceding the event and continue up to 20 minutes before the start. Your stomach requires that much time to empty. Carbo loading will increase your water loading yield. In order to store each gram of glycogen, the body has to store 2.7gms of water. It is possible to consider yourself optimally hydrated when you urinate frequently and your urine is clear.

During performance take all the plain water you can get. This is particularly important for events of 30 minutes and over. Ideally water intake should match sweat loss and a prehydrated athlete has more water to spare, meaning better times and improved recovery. Cold water leaves the stomach far more quickly than room temperature water. Sip, don't gulp and stay away from the carbonated drinks that slow absorption. The single most important factor that affects the rate of water emptying is its glucose content. The more glucose present, the slower the gastric emptying time. This includes commercial sports drinks containing high levels of simple sugar – don't be fooled by the false feeling of increased energy. For events of 1.5 to 2 hours or longer some additional glucose and electrolyte support may be beneficial. Fructose is the preferred choice as it doesn't stimulate insulin release like glucose does, and also replaces liver glycogen better.

Rehydrate – With plain, cold water, sipped, not gulped. Avoid everything in the goody bag until you are at least four glasses ahead, to avoid cramps and possible nausea. Continue to drink extra for the following 12 – 36 hours. To establish when hydration has been adequately recovered, you should weigh yourself prior to training or competing and again afterwards, ensuring you have drunk the equivalent amount of water lost. As a rough guide 1 pint of water equals 1 pound of lost weight. If you calculate water loss as a percentage of body weight, losing more than 1% of bodyweight can have serious consequences. The major electrolytes lost during exercise in sweat can be found in fresh fruit and vegetables, (including salt). Ensure you diet contains plenty of these.

The message is use water for what it is, the main component of your body and keep it as pure as possible, either bottled or filtered. Drink small regular amounts frequently. Drink your water fridge temperature. Do not rely on the thirst mechanism. Rehydrate using the one pint to one pound principle. Consider electrolyte replacement when exercise exceeds 1.5 hours. Carbohydrates store water – carbo load 6 days prior to competition. Keep dietary intake of fresh fruit and vegetables high. Where indicated appropriate testing of mineral levels can be carried out by a registered nutritional therapist.

Christina Robilliard is a former member of the Serpentine Running Club, and a registered nutritional therapist.