Dehydration Dr Rob Hicks Most people get dehydrated from time to time, and usually it's easily corrected. But occasionally, when a lack of fluids puts the body under additional strain, it can have tragic consequences.

In this article

What is it? What are the causes?

What are the symptoms? Who's affected?

How's it prevented? What's the treatment?

Water makes up around 70 per cent of the human body. It's important for digestion, joint function, healthy skin and removal of waste products.

Dehydration occurs when more fluid is lost from the body than is taken in

Dehydration occurs when more fluid is lost from the body than is taken in. This causes an imbalance in important minerals, such as sodium and potassium, which are required for muscle and nerve function.

If there is a one per cent or greater loss in body weight because of fluid loss, dehydration occurs. This may be mild, moderate or severe, depending on the amount lost.

At one end of the scale, mild dehydration may cause someone to feel only a little thirsty. At the other end, severe dehydration can result in death.

Around two-thirds of the water we need comes from drinks. Up to one-third comes from food (tomatoes, cucumber, fish and poultry are good sources). Some is also provided as a result of chemical reactions within the body.

The average adult loses around 2.5 litres of water every day through the normal processes of breathing, sweating and waste removal. If we lose more fluid than usual this tips the balance towards dehydration.

Illnesses that can lead to dehydration include gastroenteritis (through diarrhoea and vomiting), fevers (sweating) and diabetes (excessive passing of urine).

Lifestyle factors such as drinking too much alcohol, exercise, being in a hot environment or being too busy to drink liquid can also lead to dehydration.

The main symptom of dehydration is feeling thirsty.

In mild to moderate dehydration, other possible symptoms include:

• Dry mouth, eyes and lips
• Headache
• Tiredness
• Dizziness or light-headedness
• Decreased urine output
• Muscle weakness

When dehydration is more severe, a person may experience:

• Extreme thirst
• Very dry mouth and eyes
• Loss of elasticity in the skin, making it look shrivelled
• Passing small amounts of dark, concentrated urine
• Sunken eyes
• Lack of sweating
• Fast heartbeat

In addition, blood pressure may be low, and delirium and loss of consciousness may occur.

In children, the signs to look for include:

• Dry mouth
• Fewer wet nappies or not passing urine for six to eight hours
• Irritable behaviour
• Few or no tears when crying
• Sunken or flatter than usual fontanelle (the soft spot on top of a baby's head)
• Dry and wrinkled skin
• Being less alert and less active than usual
• Appearing weak
• Fast pulse
• Fast breathing

Long-term dehydration may contribute to other health problems, such as constipation, kidney stones and fatigue.

Anyone's at risk of dehydration, but some people are more at risk than others.

• Babies and young children have relatively low body weights, making them more vulnerable to the effects of fluid loss.
• Older adults tend to eat less and may forget to eat and drink during the day. With increasing age, the body's ability to conserve water decreases and a person's sense of thirst becomes less acute. Illness and disability are also more common, which may make it harder to eat and drink enough.
• People with long-term medical conditions, such as kidney disease and alcoholism, are more at risk of dehydration.
• Short-term, acute health problems, such as viral infections, can result in dehydration because fever and increased sweating mean more fluid is lost from the body. Such illnesses may also make you feel less inclined to eat and drink.
• People living or working in hot climates or those who take part in sports or other strenuous physical activities are at greater risk of dehydration.

The key to avoiding dehydration is to eat and drink enough. The Food Standards Agency recommends drinking at least six to eight glasses (around two litres) of water every day.

In addition, it recommends drinking semi-skimmed milk, diluted fruit squash and diluted fruit juice to contribute to the recommended daily intake of fluid.

People living or working in hot climates or taking part in sports or other strenuous physical activities, or who are unwell with vomiting and diarrhoea, should increase their fluid intake.

For every hour of exercise, it's suggested you drink an additional litre of fluid, more if exercising in a warm environment.

Mild dehydration is easily treated by drinking water and other fluids, such as diluted fruit juice.

For the ideal replacement of fluid and minerals, particularly when vomiting and diarrhoea are making fluid consumption difficult, rehydration treatments are available from the pharmacist.

More severe dehydration can be life-threatening and usually requires hospital treatment, which involves intravenous fluids to correct the water and electrolyte imbalance.

This article was last medically reviewed by Dr Rob Hicks in January 2008