Some age groups are especially sensitive to the effects of dehydration; some people also have special hydration needs due to particular conditions.
About 60% of the typical adult human body is made up of water, but the percentage is strongly influenced by the level of body fat. The higher the level of fat, the smaller the fraction of body weight that is made up of water. In newborn children the percentage of the body that is made up of water reaches around 75% and this falls during growth and maturation. Infants and young children may be especially at risk of dehydration due to diarrhoea and vomiting. Because they often cannot communicate their needs, those looking after them need to be alert to the possibility of dehydration, especially during hot weather or during periods of illness.
Active children playing games in hot weather may lose large amounts of sweat, but they are often so involved in what they are doing that they forget to drink. Those looking after them may need to offer periodic reminders.
There is some evidence that providing drinks to children can help them to perform better in standardised tests of concentration, short term memory and other essential elements of the learning process. More evidence is needed before definitive guidelines can be given, but teachers may need to make sure that there are opportunities for drinking during the school day and that children are reminded to make use of these opportunities.
The European Food Safety Authority (EFSA)* has concluded that adequate intakes of water for children are as follows: 1,300 mL/day for boys and girls 2 to 3 years of age; 1,600 mL/day for boys and girls 4 to 8 years of age; 2,100 mL/day for boys 9 to 13 years of age; 1,900 mL for girls 9 to 13 years of age. Adolescents of 14 years and older are considered as adults with respect to adequate water intake and the adult values apply.* EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. doi:10.2903/j.efsa.2010.1459. Available online:www.efsa.europa.eu
With age, the body loses its ability to detect thirst. Therefore, to stay sufficiently hydrated, elderly people should anticipate the body’s needs and not always wait until they are thirsty to have a drink. To prevent dehydration, it may be best to drink on a regular basis. Ideally, elderly people should get into the habit of drinking one or two glasses of beverage with each meal and drink occasionally during the day when they aren’t eating.
Usually people drink when they are thirsty, and simply relying on the thirst signal will normally ensure that they drink enough to stay well hydrated. But by the age of 60, if people only drink when they are thirsty, they may not get as much water as they need. The problem continues to get worse as they get older.
Dehydration can cause serious problems in older adults. Elderly people are at greatest risk of dehydration and its potentially life-threatening consequences. People aged between 85-99 years are six times more likely to be hospitalized for dehydration than those aged 65-69 years. Mild dehydration may also cause conditions such as constipation.
Women who are pregnant or breastfeeding may be at greater risk of developing dehydration particularly during early pregnancy if vomiting or diarrhoea are present. During pregnancy, the hydration needs will change and the child’s health depends on the mother. Throughout these months, hydration plays an essential role since an adequate supply of water is essential for the renewal of amniotic fluid, the baby’s living environment. Water represents 94% of the baby’s weight at the end of the first trimester. It is important to drink enough in order to meet the new needs of the body and the baby during pregnancy. The European Food Safety Authority (EFSA)* has concluded that due to the increase of body weight and of energy intake, an additional total water intake of 300 mL on top of the 2 L would be adequate
Breastfed babies take in an average of about 750 mL of milk per day between the ages of 1 month and 6 months. Different babies take in different amounts of milk and the typical range of milk intakes is about 600-900 mL per day. Breastfeeding mothers therefore lose significant amounts of fluid during nursing and need to increase their fluid intake. Mild dehydration does not affect milk supply, but moderate to severe dehydration may have an effect, including changing the composition of the milk and decreasing the amount of milk produced. Dehydration will also add to feelings of tiredness at what can be a very stressful time. The European Food Safety Authority (EFSA)* has concluded that water intake for lactating women should compensate the loss of water through milk production i.e. an additional amount of 600 – 700 mL should be added to the 2 L reference daily intake.* EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. [48 pp.]. doi:10.2903/j.efsa.2010.1459. Available online: www.efsa.europa.eu.