Water is one of the body’s most essential nutrients, yet one that many people ignore.
Your body is made up of about 60% water – in fact, muscle tissue is about 72% water. If your water levels fall significantly below this, you enter into a state of dehydration. This can have serious effects on your health.
Water Balance
Your body’s needs for water are met through three sources: fluid intake, such as water or juice; foods – fruit and vegetables particularly have a high water content; and metabolic reactions.
There are four avenues of water loss from the body: urine, sweat, exhalation from the lungs, and in faeces.
Under normal circumstances, your body maintains a state of hydration – the balance between water intake and water output.
When vigorous exercise is added to your daily routine, there can be a shift in water balance. By taking careful steps to prevent this you can stay well hydrated.
Exercise and water loss
Increased body temperature is dangerous and can be fatal, so the body
has effective mechanisms for heat removal.
The primary method is sweating.
During exercise, your body generates a great deal of extra heat, as a by-product of muscle contraction. The body responds to this by increasing the volume of sweat produced. In addition, increased breathing increases the loss of water from the lungs.
In this way, up to a litre of water can be lost from your body in an hour of exercise. If this is not replaced, both reduced performance and health risk will develop.
Thirst
Thirst is the mechanism that your body has to tell you that you are heading for dehydration. Unfortunately, under situations of rapid fluid loss, you may not get thirsty until you are already approaching dehydration.
During exercise, or in conditions of great heat or humidity, it is far more effective to consciously adopt a strategy to prevent dehydration.
In simple terms this means drinking fluid before, during and after exercise.
What to drink
Your body’s main need will be for water, so this is what you should drink. Drinks containing small quantities of sugar or electrolytes are also good. These, however, should be quite dilute, as sugar can slow down the rate of absorption of fluids.
Guidel
ines for fluid intake and replacement
- A sedentary person needs about 8 glasses of water per day.
- Drink 2 glasses (300-500ml) of fluid 15-20 minutes before heavy exercise and 1 glass (150-200ml) at 15-20 minute intervals throughout the exercise. Continue drinking after exercise.
- If competing in endurance activities (e.g. in a marathon), take regular drinks stops from the start. Because it takes time for fluids to pass through the system, these should be ingested before thirst is felt.
- The most important consideration is the replacement of water. Sports drinks containing small quantities of electrolytes and sugar may be useful in prolonged exercise (over 1 hour).
- Drink fluids that are cool (10-15°C) in order to speed emptying time from the stomach.