Water is vital for the proper functioning of all body organs. Thus we need to replenish any fluids that are lost, says medical student Maria Angela Grima.

The elderly have a weaker thirst sensation which hinders them from replenishing the water lost throughout the day.

Water makes up about 60 per cent of our total body weight. Small amounts of fluid are lost continuously during the day while breathing, and also via the skin, urine and excreted matter. But excess amounts are lost during exercise: water evaporation through the skin during sweating accounts for about 0.45 litres of water lost per day. A large amount of water is also lost when subject to diarrhoea and vomiting.

Loss of water in turn affects the function of all body organs, including blood pressure control, brain function, digestion and metabolism; and in the long term, leads to decreased lubrication of joints and dry, wrinkly skin.

Evidence shows there is a strong association between long-standing mild dehydration and kidney stones, urinary tract infections, high blood sugar in people with type 1 diabetes mellitus and heart valve problems.

Who is at risk?

A number of factors affect the total amount of water lost, including gender, body size, the level of physical activity and also the amount or type of clothing worn. Water loss through the skin is also affected by the environmental temperature and humidity, both indoor and outdoor, hot and cold climates.

Extremes of age are associated with dehydration. Infants have a body water content that is about 15-25 per cent higher than that of adults. Like children, they do not communicate their thirsty needs easily and need additional water to meet the needs of their high metabolic rate. The immune system is less mature in infants and children, making them more prone to bacterial and viral illnesses that cause vomiting and diarrhoea.

On the other hand, the elderly have a weaker thirst sensation which hinders them from replenishing the water lost throughout the day. Their declining kidney function also affects water balance since they experience a reduction in water reabsorption. Additional factors such as physical immobility, memory and communication problems lead to decreased consumption of water.

The elderly may also be on medications which could alter their fluid balance by increasing urinary water loss, blocking the thirst sensation and affect hydration in other ways. They must therefore include additional amounts of water in their diet to avoid potentially life-threatening dehydration.

How to recognise dehydration

Mild dehydration occurs when about one per cent of body weight is lost. Symptoms may not be so obvious, but may include thirst, headache, fatigue, nausea and vomiting, light-headedness when standing from a sitting position and lethargy. Increased water reabsorption by the kidney occurs, so the urine will be darker and more concentrated.

Moderate dehydration occurs when about four to 10 per cent of body weight is lost. This is known as clinical dehydration, whereby symptoms and signs are more obvious. These include dry mouth, little or no urine, high heart rate and respiratory rate. In children, one must also look out for irritability or altered consciousness, sunken eyes and reduced skin turgor, particularly when they have a higher fever or have had severe bouts of vomiting or diarrhoea.

Most people do not have an adequate thirst sensation that drives them to drink

Severe dehydration will bring about shock, and this occurs when more than 10 per cent of body weight is lost. Symptoms range from extreme thirst, absence of urine, rapid breathing rate and heart rate to a decreased level of consciousness and cold, clammy skin. In children, these additional signs should be sought for and immediate action taken: grossly sunken eyes, sunken infant fontanelles and pale skin colour. This is a life-threatening event and patients must be taken immediately to hospital.

Notwithstanding the importance of these symptoms and signs, most people do not have an adequate thirst sensation that drives them to drink and hence their fluid intake over the day will not be adequate enough to replace the water lost and manage their salt balance. This is why the most reliable sign of dehydration is a low urine output, which leads to infrequent visits to the bathroom and the production of minimal amounts of dark-coloured concentrated urine.

Prevention and treatment

The European Food Safety Authority estimates that anyone over 14 years of age requires two litres (females) and 2.5 litres (males) of water per day. However, every person’s daily requirement varies from another’s since it depends on the person’s diet, environment, age and activity level.

Some people may not want to consume large amounts of plain water, so beverages such as tea, coffee, fruit or vegetable juices and soups aid as a substitution since they contain between 80-95 per cent water. Even though caffeine-containing beverages such as soft drinks and coffees contain water, one must limit their consumption to about two to three per day since these increase urine output and hence may lead to dehydration. Milk is also essential since it is a source of calcium and contains around 85 per cent water.

Besides being sources of vitamins and fibre, vegetables such as lettuce and fruit, such as watermelons, apples, oranges, grapes and strawberries, contain more than 80 per cent water.

On the other hand, strong alcoholic drinks and spirits will only promote water loss, and are recommended only in small amounts.

At school, children should be given drinks before playing with their peers. Sufficient evidence also shows that drinking helps children in their concentration, short-term memory and other elements of the learning process, so they should be encouraged to drink during school hours too.

If an infant or child develops signs and symptoms of dehydration from acute gastroenteritis, breastfeeding should be continued in addition to the daily amount of fluids given.

The elderly should be provided with meals consisting of a variety of water-containing foods, with additional drinks in between meals, especially in hospital settings where dehydration occurs quickly.

Nonetheless, their medications should be reviewed since one must keep in mind that some medications (such as bumetanide) will require the patient to limit the amount of fluids consumed during the day, especially if given for heart failure or renal failure.

During intense exercise, one must drink plenty of water before, during, and after the physical activity. Lightweight, loose clothing should be worn, since this allows sweat to evaporate.

Dr James Gauci reviewed this article.