Dehydration – Causes, signs and treatment

The human body can last weeks without food, but only days without water. The body is made up of 50 to 75 per cent water. Water forms the basis of blood, digestive juices, urine and perspiration, and is contained in lean muscle, fat and bones. It lubricates the joints and eyes, aids digestion, flushes out waste and toxins and keeps the skin healthy.

As the body can’t store water, we need fresh supplies every day to make up for losses from the lungs, skin, urine and faeces (poo). The amount we need depends on our body size, metabolism, the weather, the food we eat and our activity levels. 

Dehydration occurs when your body loses more fluid than you take in.When the normal water content of your body is reduced, it upsets the balance of minerals (salts and sugar) in your body, which affects the way that it functions.  

What causes dehydration?

Dehydration is usually caused by not drinking enough fluid or by fluid that is lost and not replaced. The climate, the amount of physical exercise you are doing and your diet can also contribute to dehydration. You can also become dehydrated as a result of an illness, such as persistent vomiting and diarrhoea or sweating from a fever, exercising in hot conditions, consuming alcohol, or too much caffeine.

Signs of dehydration

Dehydration can be mild, moderate or severe, depending on how much of your body weight is lost through fluids. Two early signs of dehydration are thirst and dark coloured urine. This is the body’s way of trying to increase water intake and decrease water loss.

Other symptoms may include:

  • dizziness or light-headedness
  • headache
  • tiredness
  • dry mouth, lips and eyes
  • passing small amounts of urine infrequently (less than three or four times a day)


Dehydration can also lead to a loss of strength and stamina. It’s the main cause of heat exhaustion.

You should be able to reverse dehydration at this stage by drinking more fluids, without medical attention. If dehydration is ongoing (chronic), it can affect your kidney function and cause kidney stones to develop. It can also lead to:

  • liver, joint and muscle damage
  • cholesterol problems
  • constipation


Treatment of Dehydration

The best way to treat dehydration is to re-hydrate the body by drinking plenty of fluids, such as water, semi-skimmed milk,diluted squash or diluted fruit juice. A sweet drink can help replace lost sugar and a salty snack can help replace lost salt. Re-hydration solutions can also be purchased at the pharmacy.

Approximate adequate daily intakes of fluids (including plain water, milk and other drinks) in litres per day include:

  • infants 0–6 months – 0.7 (from breastmilk or formula)
  • infants 7–12 months – 0.9 (from breastmilk, formula and other foods and drinks)
  • children 1–3 years – 1.0 (about 4 cups)
  • children 4–8 years – 1.2 (about 5 cups)
  • girls 9–13 years – 1.4 (about 5-6 cups)
  • boys 9–13 years – 1.6 (about 6 cups)
  • girls 14–18 years – 1.6 (about 6 cups)
  • boys 14–18 years – 1.9 (about 7-8 cups)
  • women – 2.1 (about 8 cups)
  • men – 2.6 (about 10 cups).


It’s important to remember that these are just guidelines, and some people will require more fluids at various times. For example, people need to increase their fluid intake when they are:

  • on a high-protein diet
  • on a high-fibre diet, as fluids help prevent constipation
  • pregnant or breastfeeding (the fluid need is 750-1,000 ml a day above basic needs)
  • vomiting or have diarrhoea
  • physically active
  • exposed to warm or hot conditions.


Infants, children, and the elderly are most susceptible to dehydration, and should be closely monitored – if symptoms persist, visit your GP.

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