Who is most at risk of dehydration?

• People whose water needs increase rapidly. For example, in those doing heavy manual work or exercise, particularly in hot weather, and for those who have fevers.s
• People who don't notice when they are thirsty or who don't drink when they are thirsty. This is a problem, particularly in elderly people whose attention wanders, and frequently in those who are very busy.
• People who quench their thirst with diuretic drinks. These are drinks which increase the body's production of urine. Examples are alcoholic drinks and drinks containing caffeine.

What are the side effects of inadequate water intake?

Common side effects of mild dehydration include:

• dry mouth
• lack of concentration
• fatigue
• sleepiness
• headaches

Prolonged periods of mild dehydration cause:

• bad breath and dental caries due to decreased saliva(saliva normally rinses out the mouth completely)
• confusion and feelings of being unable to cope
• swelling (oedema) in feet, legs and hands
• the risk of kidney stones because the urine passing through the kidneys is more concentrated
• increased symptoms in gout sufferers

Severe dehydration can cause:

• overheating from decreased sweating and cooling by evaporation
• heart problems
• hallucinations
• coma
• death

Is thirst a goods indication of the need to drink more fluids?

Not necessarily. Thirst can be slow in developing when more water is needed quickly, for example in hot weather with heavy exercise. Also many people are not aware of thirst signals or confuse thirst signals with hunger signals or don't get around to drinking more water when they notice early signals. Awareness of early thirst signals tends to diminish if those signals are not habitually acted on.

Thirst is a satisfactory indication of the need to drink when:

• the body's need for water develops gradually over time.
• the individual notices early thirst signals, and
• action is taken to drink more water

When are fluid requirements increased?

Whenever there are increased fluid losses from the body, water intake must be increased to replace it. Losses may occur through:

• the skin from increased sweating, or after sun damage, especially burns
• the lungs; such as hot dry conditions, air conditioning
• the nose through continual or heavy discharge of mucus
• the gastrointestinal tract; by vomiting, diarrhoea or laxative abuse
• urine; e.g. with the use of diuretics
• blood loss
• milk secretion in breast feeding mothers

Fluid requirements are also increased when losing weight(intentionally or not) and when certain foods and drinks are consumed, espacially when there is a high intake of salt, fiber, protein, caffeine, or alcohol.

Increased fluid intake is also needed for people suffering from such disorders as

• chronic constipation
• chronic diarrhoea
• chronic pulmonary disease, asthma, bronchitis
• gout
• kidney stones
• uncontrolled diabetes mellitus and diabetes insipidus

How does thirst relate to a need for more fluid?

Thirst is a physical sensation. It stimulates a desire to drink more fluid. The thirst sensation is controlled by the mouth and the hypothalamus - a part of the brain that also controls body temperature, appetite and sodium concentration of the blood.

When sodium concentration in the blood is too high, recpetors in the hypothalamus are stimulated and thirst messages are sent to the brain to initiate behviour to quench thirst. At the same time the hypothalamus activates the release of an anti-diuretic hormone, to decrease water loss at the kidneys, causing urine that is excreted to be more concentrated.

How do fluid requirements change through life?

Infants:
Infants who are breast fed or formula milk fed in cold climates can obtain all their fluid requirements from breast or formula milk - 500 to 1000ml a day. In hot climates cooled boiled water is also needed because of increased sweating and moistening of expired air.

Children:
Children older than 2 years need 1000ml to 1500ml of fluid each day. Requirements increase from infancy because of a larger body size and increased physical activity. In hot climates, additional water is needed because of increased sweating.

Pregnancy:
Fluid requirements are greater during pregnancy becuase of increased flow of urine through the kidneys to help remove increased body wastes.
During pregnancy, alcohol should be avoided and caffeine-containing drinks such as coffee, cola, and tea need to be restricted. Alcohol crosses the placenta to the foetus. Caffeine is cleared from the body more slowly during preganancy, and may also cause the foetal heart rate to slow down.
Coffee also increases the secretion of stomach acid and decreases oesophageal sphincter pressure. These effects may contribute to nausea and vomitting.

Lactation:
A greatly increased amount of fluid is required during lactation, especially water. The usual amount of milk secreted is between 850ml to 1200ml each day. At least 4 to 6 cups of fluid above the usual intake is required.

Welcome to Drinks in your diet

Without your daily fill of drinks life would not be as enjoyable, and health would detriorate rapidly. 'Drinks in your diet' is going to start with a series about health and the drinks in your diet, starting with 'Fluid Requirements'.
Did you know that 2-3 litres of water is lost from the body each day. In hot weather this can be more like 3.5 litres, and as much as 6-7 litres with exercise, and in some illnesses.

A minimum of about a litre is lost each day from the body. Water is evaporated out of the lungs and mouth through breathing, about 350ml diffuses out through the skin whether there is adequate water intake or not. Also, a minimum of 500ml of urine each day is expelled to rid the body of waste.

The main sources of water for the body is the fluid we drink and the food we eat. Humans also produce some water when fuel (glucose) is metabolised for energy.