Water intake and hydration physiology during childhood - Consumption
Physiology I. Characteristics of water physiology from infancy to adolescenceI.1. Body water contentI.2. Body water balanceI.2.1. Main water losses in childrenI.2.2. Water gainsI.3. Body water balance regulationI.3.1. Regulation by kidneysI.3.2. Thirst mechanismI.3.3. ThermoregulationHealth importanceII. Importance of adequate hydration for children's healthII.1. Assessing risk of dehydrationII.2. Hydration status and physical activityII.2.1. Effects of dehydration during physical activityII.2.2. Are children affected differently than adults during exercise?II.2.3. Water consumption and physical activityII.3. Hydration status and cognitive functionII.3.1. What is cognition?II.3.2. The impact of dehydration on cognitive function in childrenII.3.3. Beneficial effect of increasing water intakeConsumptionIII. The Challenge of hydration in childrenIII.1. Total water intakes and fluid consumption in childrenIII.1.1. Guidelines for total water intakeIII.1.2. Fluid consumption in childrenIII.2. Improved water intake: a corner-stone of childhood lifestyle programsIII.2.1. The promisingeffect of water intake on overweight preventionIII.2.2. A priority action for a healthier lifestyle in childrenIII.2.3. Action worldwide: example of a long-term development programAs a conclusionReferencesQuiz
Guidelines for total water intake have been established by many regional and global authorities (EFSA, IoM, WHO). However, in contrast to other nutrients, there is insufficient research into the amount of water required to prevent disease or improve health. As a result, neither upper nor lower consumption thresholds have been linked to a specific benefit or risk. Several methods have been used to set adequate water intakes. Most are based on intake surveys and theoretical calculations, and there is therefore a great amount of variability in worldwide reference values (Table 1).
In the USA and Canada, adequate intakes of water in children are based on the median water intake from NHANES III data (Third National Health and Nutrition Examination Survey) (IoM, 2004).
The most recent official guidelines for total water intakes have been published by the European Food Safety Authority (EFSA) in 2010. In children, adequate intakes are based on observed intakes in studies in which the contribution of water from food could be evaluated, adjusted to reach an available water amount of 1 mL/kcal ingested and take into account the variations between individuals.
Based on guidelines, children have specific water needs until puberty, compared to adults (Table 1). By pre- adolescence, boys have higher recommended intake than girls.
Table 1. Reference values for total water intake (food + fluid) per age group.
These references for total water intake include both water from food plus water from beverages of all kind, including drinking and mineral water. For adults, it is considered that the contribution of food to total water intake represents about 20% (EFSA, 2010). No evaluation has been completed for children so far.
The EFSA has not set maximal safety intake levels, due to the ability of kidney in healthy individuals to excrete excessive water intakes, up to 0.6-1liter of urine per hour for adults (Noakes et al., 2001).
Available data suggest that children do not drink enough and do not meet the daily recommended intake. According to observational data from NHANES (USA), in children and adolescents between 4-19 years of age the mean daily total water intake is lower than the IoM adequate intake (beverage and food moisture) (Kant et al., 2010). Results from the DONALD study (Germany) indicate that 49% of boys and 29% of girls between 4-11 year of age were considered not sufficiently hydrated (Stahl et al., 2007). Moreover, while contribution of plain water (from 22% in 2-5 years old to 33% in adolescents) to water intake increases with age, main contributors of to water intake are beverages, i.e. all types of fluid except drinking water. Beverages account for 52% in 2-5 years old and 47% in adolescents.
A recent study has revealed that among healthy children (9-11 years old), 75% of the children did not drink water before going to school. Naturally, urine osmolality was elevated in those who did not drink anything before school. However, what was more surprising was that urine osmolality was also elevated in children who drank large volumes of beverages other than water (Stookey et al., 2011). Drinking water fulfills hydration requirements without increasing solute load presented to the kidney and hence elevated urine osmolality. These data suggest that schoolchildren may be at risk of suboptimal water intake relative to IoM, EFSA or WHO guidelines.
Childhood obesity is a global epidemic. In 2010, 43 million children (35 million in developing countries) were considered overweight and obese (Figure 6) and 92 million were at risk of overweight (de Onis et al., 2010). The worldwide prevalence of overweight and obesity increased by 60% between 1990 and 2010 (de Onis et al., 2010) and in some countries (in the US in particular) the proportion of overweight children has tripled since 1980 (WHO, 2006).
Figure 6. Numbers (in millions) of overweight and obese children aged 0 to 5 years old: 1990-2020.
(Adapted from de Onis et al., 2010).
Weight gain in childhood is a real concern because it is a strong determinant of adult obesity (de Onis et al., 2010, Guo et al., 1999, Symonds et al., 2011).
Healthy eating is one of the key actions for obesity prevention, and healthy fluid consumption is part of a balanced diet. Water ingestion is commonly believed to reduce energy intake, however few studies have investigated the direct effect of water on weight management in children.
Recently, a study has shown that the promotion of healthy hydration in elementary schools, by increasing water accessibility through water fountains and providing lessons to promote water consumption, was an efficient strategy to lower the risk of being overweight by 31% in the interventional group (Muckelbauer et al., 2009).
A study of overweight children reported that consuming 10 mL/kg cold water can temporarily increase resting energy expenditure for at least one hour after consumption. While the observed metabolic increase was short-term and temporary, the authors extrapolated that if children would consume the recommended daily amount of water, this increase in energy expenditure would represent a weight loss of 1.2 kg per year (Dubnov-Raz et al., 2011). Given that data is limited, more research would be required to establish whether this strategy would be effective in real life conditions.
These first results suggest that increasing water consumption may have a positive impact on weight management in children. Then, if it proves to be an effective action, drinking water programs may contribute to weight management in children. Public health authorities are putting more and more emphasis on the importance of a healthy diet and physical activity in preventing of overweight and obesity in children and adolescents.
In response to the growing burden of obesity, policy frameworks are introduced, particularly with respect to health promotion for children. They are based on modification of lifestyle practices such as physical activity, as well as encouraging a balanced diet, including recommendation to favor drinking water over other beverages. Some examples are presented below:
In 2004, The Global Strategy on Diet, Physical Activity and Health was adopted by the WHO. In this context, more recently a set of tools to guide member states while setting their national action plan was published. Increasing the consumption of water in children has been identified as a priority area for action in the field of preventing childhood obesity (WHO, 2012).
- Among its guidelines, the Institute of Medicine (2007, pp5) also encourages water as a healthier alternative at school: “Schools should make plain, unflavored water available for free throughout the school day, either in the form of bottled water or from water fountains”.
- Similarly in France, the National Plan for Nutrition and Health (PNNS, 2008) recommends: “Water can be consumed without restraint during and between meals. To stay healthy, water is the only drink necessary. Water is the best drink that quenches thirst without adding calories”.
- In the vein of this ambition, programs are being lead internationally. For example, the Food and Nutrition Service, part of US Department of Agriculture (2010), recently launched an initiative aimed at tackling childhood obesity. Although it is too early to conclude whether it is effective, the “Let’s Move” program supports simple actions, such as recommendations for healthy eating pattern in school and at home, better food labeling, and increased daily physical activity for children. Among the healthier alternatives proposed, the one to make better beverage choices, choosing water instead of sugar-sweetened beverages.
Finally, findings from recent randomized controlled trials show that consuming noncaloric instead of caloric beverages diminishes weight gain in children and adolescents (de Ruyter et al., 2012, Ebbeling et al., 2012).
Childhood lifestyle programs recognize the importance of good hydration with water preferably by including it as part of key lifestyle measures. Some have already shown encouraging results.
The EPODE program (Ensemble Prévenons l’Obésité des Enfants – Together Let’s Prevent Childhood Obesity) is a program of local interventions to prevent childhood obesity. Its objective is to develop in different countries a methodology to prevent obesity. This program involves all stakeholders of a community to encourage families to adopt a healthy lifestyle (balanced diet and physical activity). Among others, promoting healthier fluid intakes in children and adolescent is included in the prevention actions. A pilot study launched in 1992 in two French towns showed that the prevalence of overweight in children between 5 and 12 years old was significantly lower in both pilot towns compared to control ones, respectively 8.8% vs. 17.8% (Romon et al., 2008). Since its official launch in 2004, the program has been broadly implemented within France. Moreover, the model has also been adopted in 5 other countries (Table 2).
Table 2. EPODE long-term programs developed throughout the world.
The latter two programs have developed specific actions to promote healthy fluid intake. The OPAL theme “Water: The Original Cool Drink” aims to encourage children to replace sweetened drink consumption with plain tap water.
There is a consistent agreement among public health authorities and scientific societies regarding water and other types of fluid intakes. Water is a healthy choice at any time and the only fluid the body needs. It has no calories, no sugars and no additives. In consequence, water should be the preferred beverage for hydration.
Take home messages
In children, most of the guidelines for total water intake are based on intake surveys and theoretical calculations, and there is therefore variability in worldwide reference values.
Based on guidelines, children have specific water needs until adolescence, which are different from those of adults.
Childhood obesity is increasing worldwide and represents a major issue because weight gain in childhood is a strong determinant of adult obesity.
Water is a healthy choice at any time. It has no calories, no sugars and no additives. In consequence, water is recommended as the beverage of choice by numerous professional organisations.
Improving water intake is increasingly considered as a priority action for healthier lifestyle in children.