Water is essential for health and vital for all bodily functions. If water losses are not replaced then dehydration can occur and even mild dehydration is associated with negative effects on health including impaired cognitive function. Studies in schoolchildren have found that many are arriving at school with a hydration deficit and, once they arrive, they are not drinking enough fluid throughout the day to maintain adequate hydration levels, thus potentially affecting their performance at school. Therefore, there is a need to highlight the importance of adequate hydration among schoolchildren. However, there is often confusion among parents, carers, health professionals and teachers about how much fluid children need to drink, as well as what drinks are most appropriate. This article provides a summary of the development of the Healthy hydration guide for children that was produced to help parents, carers, health professionals and teachers, and indeed children themselves, to choose a healthy balance of drinks to ensure optimal performance and health. It is hoped this resource will help children aged 4–13 years to establish healthy drinking behaviours.
Water is essential for life – the body cannot normally survive for more than a few days without it. Water is fundamental for all bodily functions and performs vital roles such as transporting nutrients and waste products between major internal organs in the body, helping regulate body temperature and lubricating moving parts – water also aids in metabolism and digestion (Jequier & Constant 2010). Water is constantly being lost from the body, not only from urine and faeces, but also through the skin and via breath, so this must be replaced regularly by fluid from the diet or dehydration can occur. Dehydration can be defined as a 1% or greater loss of body mass due to fluid loss (Kleiner 1999). Dehydration resulting in loss of 2% or more body mass can lead to impaired cognitive function, reduced physical performance, headaches and symptoms of fatigue. Chronic mild dehydration (i.e. loss of 1–2% body mass over a period of time) is associated with increased risk of several conditions including urinary tract infections and constipation. The body has a series of mechanisms to avoid dehydration; these include reducing the amount of water lost in urine, which is controlled by the kidneys, and stimulating thirst to encourage fluid consumption. Thirst is triggered when the body is already slightly dehydrated so it is important to respond to thirst in order to avoid dehydration (see Benelam & Wyness 2010).
Newborn infants have a body water content of about 75%, which decreases with age to about 60% for older children and adults. Children are less heat tolerant and more susceptible to dehydration than adults especially during physical activity and in hot climates. If a state of dehydration does occur even relatively mild dehydration (i.e. 1–2% loss of body mass due to fluid loss) can cause tiredness, headaches, lack of concentration and dry skin (see Benelam & Wyness 2010). Therefore, it is vital that children consume enough fluid throughout the day to stay properly hydrated for optimum health and to establish healthy drinking behaviours.
All (non-alcoholic) drinks contribute to hydration and many foods also provide some fluid. Foods such as fruits and vegetables, yogurt, soup and stews all have a high water content. On average, it is estimated that food provides between 20% and 30% of total fluid intake, while drinks provide the rest (70–80%) (EFSA 2010).
Developing sensible guidelines for healthy hydration in children
In 2009, the British Nutrition Foundation (BNF) published a review on hydration and health (Benelam & Wyness 2010), which was accompanied by a ‘Healthy Hydration Guide’ giving practical advice for adults on choosing a healthy balance of drinks. The guide proved to be a popular resource for health professionals and consumers. However, it was not suitable for younger children. To fill the gap, in 2012 BNF collaborated with the Natural Hydration Council (NHC) to provide advice on healthy hydration in children aged 4–131 years for the development of a visual guide, the Healthy hydration guide for children, with an accompanying commentary providing supportive information on this topic. The main aim of the children's hydration guide was to provide sensible guidelines about the approximate amount children should drink and which drinks are most appropriate, to help care providers, parents, teachers and health professionals make informed choices about suitable drink provision for children. This article outlines the background and advice given to the NHC by the BNF which led to the development of NHC's healthy hydration guide for children. A BNF resource has also been produced which is available on the BNF website: www.nutrition.org.uk/healthyliving/hydration/children (see Fig. 1).
Hydration in schoolchildren
The human brain is 73% water, so poor hydration can affect its function (Mitchell et al. 1945; Lieberman 2007). Evidence shows that dehydration (equating to <2% reduction in bodyweight in adults) can reduce concentration levels and lower cognitive and physical performance; it can also increase feelings of aggression and/or irritation (Lieberman 2007; EFSA 2011). In children, dehydration has been shown to affect cognitive function and studies have suggested that the number of children who may be dehydrated at school is alarmingly high. A study of 452 schoolchildren in the UK, aged 9–11 years (recruited from several schools from Sheffield), found 60% of children arrived at school inadequately hydrated (Friedlander 2012). Another study of 298 schoolchildren from year 2 (aged 6–7 years) and year 5 (aged 9–10 years) from six schools in Southampton found that once children arrived at school 71% did not drink enough fluid throughout the day to maintain an adequate hydration level (Kaushik et al. 2007). A recent small intervention study of 15 schoolchildren (aged 8–9 years) in the UK demonstrated that drinking an additional glass of water (∼200 ml) could significantly improve their ability in tasks that involved visual attention and fine motor skills. The authors concluded that it is likely the positive effects of water supplementation would also extend to classroom-based activities such as handwriting and copying text (Booth et al. 2012). Therefore, additional fluid in children's school day could have a positive impact on their performance at school. However, the study did not measure the children's state of hydration before the intervention so it is uncertain whether they were already in a state of dehydration, whether the additional fluid was correcting hydration levels, or whether the additional fluid added an extra benefit to being adequately hydrated. Furthermore, water was only provided during the allocated tasks so further research needs to be done on the associations between fluid supplementation throughout the day and children's performance at school.
The main barriers preventing fluid intake at school appear to be that it is not deemed ‘cool’ or fashionable to drink water and it is often difficult for children to access water throughout the school day (Molloy et al. 2008). This may be because regular consumption of water is not always encouraged due to concerns that additional trips to the water fountain or the toilet will be disruptive to lessons (Molloy et al. 2008). In addition, some children (particularly younger children) may be so involved in what they are doing that they forget to drink some fluids. In this context, it is particularly important that children are encouraged to drink fluid regularly to stay adequately hydrated. Evidence suggests that patterns of drinking behaviour appear to be established early in childhood, so it is important that young children get used to drinking water and a range of other appropriate drinks in order to maintain hydration (Saltmarsh 2001). Therefore, teachers, parents and care providers need to make sure that there are opportunities for drinking throughout the day and that children are encouraged to make use of these opportunities.
How much fluid do children need?
The amount of fluid children need depends on many factors including their age, their gender, the weather and their physical activity levels, but generally they should drink about 6–8 glasses of fluid per day (on top of the water provided by food in their diet). Younger children need relatively smaller drinks (e.g. 150 ml serving) and older children need larger drinks (e.g. 250–300 ml serving). These amounts are based on the European Food Safety Authority's (EFSA's) Dietary Reference Values for fluid, which are recommendations for adequate intakes under conditions of moderate environmental temperature and moderate physical activity levels (see Table 1).
Table 1. EFSA's recommendations for fluid intake for children [Note that these values include water from both food and drinks (amounts from drinks only have been estimated)]
Amount of fluid from drinks and food (litres/day)a
All drinks provide water and some also contain essential nutrients such as protein, vitamin C or calcium. Drinks can also provide energy (calories/kilojoules) and may contain sugar. Consuming more energy than needed over time causes positive energy balance and weight gain, so it is important to be aware of the energy content of drinks as well as foods. Furthermore, frequent consumption of sugar-sweetened drinks can increase the risk of tooth decay, especially if good dental hygiene is not practised. Dental guidelines for children recommend consuming sugar-containing food and drinks on no more than four occasions per day, including at mealtimes, to brush teeth twice a day using a fluoride containing toothpaste and to have regular dental check-ups (Walls 2009). It is also important to be aware that some soft drinks are acidic (e.g. fruit juice, squash and some carbonated drinks) and that this may cause dental erosion (damage to tooth enamel) if these drinks are consumed frequently. To reduce damage to teeth, it is recommended that sugar-containing drinks and/or acidic drinks, if drunk, are consumed at mealtimes and drunk through a straw (as a straw minimises contact with teeth and the other meal components help buffer the impact of drinks on teeth).
When the guide was developed, information was provided about the frequency with which various drinks, which might be drunk by children aged 4–13, should be consumed. This was to give users an idea of the relative contribution these drinks should make to fluid consumption. Aspects such as the presence of essential nutrients in some drinks, and that some drinks provide energy and/or are acidic (and hence may have negative effects on dental health if drunk too frequently), were also taken into consideration. Some drinks such as tea, coffee and some soft drinks may also contain caffeine, which is a mild stimulant. Caffeine is generally recognised as safe to consume in moderate amounts for most adults (pregnant women are advised to limit their intake to 200 mg/day, which equates to about two mugs of instant coffee). However, caffeine intake in children has not been adequately investigated and its effects in this age group are poorly understood. In the UK, no safe threshold of caffeine intake has been set for children, but the effects of caffeine are likely to be greater because the nervous system (including the brain) continues to develop and mature throughout childhood, which may make children more sensitive to any adverse effects (Nawrot et al. 2003). In addition, there is no age-specific threshold set for caffeine consumption in children but the Scientific Committee on Food (SCF) has explored the effects of caffeine intake and found that a dose of 5 mg/kg of bodyweight increased arousal, irritability, nervousness and anxiety in several studies among pre-school and school-aged children, particularly if they were normally low consumers of caffeine. SCF concluded that for children who are low consumers of caffeine, the intake of 160 mg/day in a 10 year old weighing 30 kg (equivalent to a dose of 5.3 mg/kg bodyweight/day) can cause temporary side effects such as irritability, nervousness or anxiety (SCF 1999). For an average 4-year-old girl, weighing about 16 kg, this equates to 80 mg of caffeine per day (equivalent to a dose of 5 mg/kg bodyweight/day or approximately equivalent to two small cups of tea). For an average 13-year-old boy, weighing about 43 kg, 5 mg/kg bodyweight/day equates to 215 mg of caffeine a day (equivalent to approximately two mugs of instant coffee or three cups of tea). Therefore, because the guide covers a wide age group of children the advice for younger children who are less caffeine tolerable should be to minimise intake of caffeine containing drinks, and for older children who are more caffeine tolerable to moderate intake of caffeine containing drinks. NHS Choices advises that neither tea nor coffee are suitable drinks for toddlers and young children (NHS Choices 2011). This is probably because there is insufficient data to support the impact of caffeine on children.
The age range covered by the guide was wide and clearly the requirements and drinking patterns of a 4 year old are very different to that of a 13 year old. However, it was felt that it would be more helpful to have a single, more general guide to provide key information for school-age children than to provide a series of different guides for different age groups. Importantly, the drinks included and the order in which the drinks are placed are not intended to be prescriptive, while it is recognised that children will not necessarily include all of these drinks in their diet. The aim was to help users choose a balance of drinks for children in this age group and to understand the pros and cons of different options.
The advice provided for children aged 4–13 in the commentary is as follows:
Drink plenty of water: water is a very good choice for children throughout the day, and especially after physical activity and in hot weather. It hydrates without providing calories (kilojoules) or risking harm to teeth.
Have milk regularly: milk is also a good choice as it contains essential nutrients such as protein, B-vitamins and calcium (important for healthy bone development), as well as being a source of water. Children from 5 years of age should be eating and drinking like the rest of the family, so semi-skimmed (less than 2% fat), 1% fat or skimmed (less than 0.1% fat) milks are preferable for most children. Semi-skimmed is suitable for 4-year-olds, unless the child is not eating well, then whole milk should be given – skimmed or 1% fat milk is not advised for children under 5 years. Soya drinks and other non-dairy alternatives are lower in saturated fat but do not contain the same range of nutrients as milk. Most non-dairy milks are fortified with calcium, vitamin B2, vitamin B12 and vitamin D2, so in preference the fortified varieties should be chosen. Some milks are sweetened and these should be drunk less often. Milky drinks prepared with powdered products containing added sugar such as milkshakes, hot chocolate and malted drinks provide water and nutrients and are often more popular with children than plain milk. However, they should be drunk in moderation, without adding extra sugar, and the powders can be made up at home using low-calorie versions and/or reduced fat milks.
Have fruit juices in moderation: fruit juices provide water plus some vitamins and minerals. One 150 ml glass of 100% fruit juice counts as a maximum of one of the recommended 5-A-DAY, so it is important to check the nutrition information on the packaging to make sure it is 100% fruit juice (some juice drinks can contain as little as 5% fruit juice and a lot of added sugar). However, the sugar naturally present in fruit juice adds energy to the diet and can increase the risk of tooth decay. Fruit juices can also be acidic, so they may cause tooth erosion if drunk too frequently. To reduce the risk of tooth damage, it is advised that fruit juice is diluted with water (especially for younger children) and that it is consumed only at mealtimes.
Can have smoothies once a day: smoothies provide water and nutrients, and may also contain pureed fruits or vegetables, which add fibre. Smoothies that contain at least 150 ml of fruit/vegetable juice and 80 g of crushed or pulped fruit/vegetable can count as a maximum of 2 portions of the recommended 5-A-DAY [fruit juice can only count as 1 portion (maximum) per day regardless of the source]. However, smoothies can contain more sugar (and therefore calories) than fruit juice and the sugar present may increase the risk of tooth decay. Smoothies can also be acidic, so could potentially cause tooth erosion if drunk often. To reduce the risk of tooth damage, it is better for children to drink smoothies only at mealtimes.
Have low-calorie soft drinks just occasionally: low-calorie soft drinks provide water without providing much energy or many nutrients (although some may have vitamins and minerals added). These drinks can be acidic and can erode dental enamel if consumed frequently. Also, some low-calorie soft drinks, such as colas, may contain caffeine, so this should be drunk less often (see above for more advice on caffeine).
Have soft drinks containing sugar just occasionally: sugar-containing soft drinks such as some carbonated drinks and squashes provide water, but they can be high in energy and the sugar can potentially cause tooth decay if these drinks are consumed frequently. They may also be acidic, so frequent consumption can increase the risk of dental erosion. These drinks should be limited and only consumed at mealtimes. Whenever possible, reduced sugar or sugar-free (low-calorie) versions should be chosen instead to prevent excess calorie intake. Also, some sugar-containing soft drinks, such as colas, may contain caffeine, so these should be drunk less often (see above for more advice on caffeine).
Have tea and coffee just occasionally (and only in small amounts if caffeinated): both coffee and tea (in smaller amounts) naturally contain caffeine (a stimulant). Milky instant weak coffee (up to 1 cup per day for younger children) or weak tea (1–2 cups/day for younger children) is acceptable in moderation. It is better for children to drink decaffeinated versions of tea and coffee and to consume these beverages with milk but no added sugar.
Drinks not suitable for children
Energy drinks are becoming increasingly popular with children, but it was decided to omit this category of drinks from the guide because they are not designed for children or teenagers. Most energy drinks contain very high amounts of caffeine and sugar, and are therefore not appropriate for this age group due to some of the points discussed previously. It was also decided not to include sports drinks in the guide as these drinks are only suitable for children who are training or competing at high intensity. In most cases, water is the most appropriate drink to replace body water that may have been lost through physical activity and sport, and it is important that fluid is provided before, during and after activity.
Practical tips to keep children hydrated
Ensure children have a drink before school (i.e. with breakfast) and before and during playtime.
Parents, teachers and care providers should offer drinks regularly, especially in hot environments and before, during and after physical activity.
Ensure that drinks are always available – water, milk, juice, low-sugar soft drinks and other fluids can all help meet a child's hydration needs.
Remember that many foods have a high water content and can also contribute to fluid intake (i.e. fruit, vegetables, yogurt).
Always pack a water bottle in a school bag or lunch box for children heading off to school/outings/other activities (EHI 2012).
There is often confusion about how much children should drink and what drinks are most appropriate, so there is a need for sensible guidelines. The guide aims to highlight the importance of hydration in children and provide information not only to help parents and carers establish healthy drinking habits in children but also to help children make healthy choices. The guidelines advise that children drink plenty of water to keep hydrated, and that other drinks such as milk, juices and soft drinks can contribute to total fluid intake. However, when using the guide it is important to be aware of some caveats: (1) the age group is wide so it is not intended to be prescriptive; and, (2) when choosing drinks it is important to consider their nutrient value, calorie content, impact on dental health and caffeine content. The BNF hope that the guide provides a useful tool to help highlight the importance of hydration in children.
Financial support was given for the production of the children's hydration guide by the Natural Hydration Council.
Conflict of interest
The author has no conflict of interest to disclose.
Adolescents aged 14 years+ are considered by the European Food Safety Authority (EFSA) as adults with respect to adequate water intake, so this guide is aimed at children aged 4–13 years.