Children's energy and nutrient requirements are relatively high in relation to their body size, especially during periods of rapid growth. For example, during adolescence (10–18 years), puberty is associated with increased requirements for energy and nutrients as illustrated in Tables 1, 2a and 2b, because of the hormonally driven rate of increase in height and weight. In boys, the linear growth spurt resulting in increased height is greater than in girls and is accompanied by an increase in muscle growth. Concurrently, the physiologically driven rapid increase in bone mass is accompanied by deposition of calcium and phosphate (see section ‘Bone development’).
Dietary reference values (DRVs)
DRVs are estimates of the requirements of energy and nutrients for groups of people, taking into account various factors that influence requirements including growth and development. DRVs are useful as a general guide for a whole population group, but they are not intended for the assessment of the needs of individuals. Examples of their use include interpreting outcomes of dietary surveys to detect low intake levels of population groups, setting standards for food provision, and planning meals in schools or hospitals. DRVs for a given nutrient comprise: (1) the estimated average equirement (EAR), which is an estimate of the average requirement for energy or a nutrient – approximately 50% of a group of people will require less, and 50% will require more; (2) the reference nutrient intake (RNI), which is the amount of a nutrient that is enough to ensure that the needs of nearly all the group (97.5%) are being met; and (3) the lower reference nutrient intake (LRNI), which is the amount of a nutrient that is enough for only the small percentage of the group (2.5%) who have low requirements.
Typically, DRVs for protein, vitamins and minerals for groups of children are expressed as RNIs. For energy, EARs are used as an indication of requirements. Use of RNI values (equivalent to the mean plus 2 standard deviations) is not suitable for energy, as this would mean that predicted intakes would be greater than most people's needs and hence would result in weight gain over a period of time. Energy requirements are influenced by physical activity levels, in particular, and can vary significantly depending on the amount of physical activity undertaken habitually. Guidelines for energy intake assume a sedentary lifestyle, as this is the situation for the majority of people in Britain, although increased activity is advised. DRVs for macronutrients are expressed in terms of food (or total) energy intake and again are population mean values rather than recommendations for individuals.
The reference values for energy intake in the UK have recently been updated by the Scientific Advisory Committee on Nutrition (SACN), using data from studies that are representative of the current UK population and that have employed the doubly-labelled water method, an objective method for measuring energy requirements that was not in use in the 1980s/early 1990s when the previous reference values were set (SACN 2011). The population EAR values are calculated at median physical activity level values for best estimates of healthy bodyweights, i.e. the 50th centiles of the UK/World Health Organization (WHO) Growth Standards (2–4 years) and the UK 1990 reference for children and adolescents (for children over 4 years of age) (also see section ‘Overweight and Obesity’). These reference weights are about 15% lower than current UK weights and thus for those children who are overweight and for any underweight children, energy intakes at the recommended levels will be associated with weight change (SACN 2011). The new EARs for younger children are lower than the EARs published in 1991, whereas for children older than 10 years, they are now higher. See Table 1 for EARs for energy for children and adolescents. These values reflect the findings of recent studies and highlight increasing requirements with age, differences between boys and girls, which become more pronounced with age, and differences in requirements between less active and more active (compared with the population average) children and adolescents.
Tables 2a and 2b show the current UK DRVs for selected nutrients for boys and girls aged 4–18 years, respectively (DH 1991). Desirable intakes of carbohydrates and fats are available for the population in general and are expressed as a proportion of total dietary energy (Table 3). These take into account eating habits in the UK and the practical implications of dietary changes in line with those considered desirable for health. They have been calculated with the needs of the adult population in mind. While these values provide a useful guide for older (school age) children, the recommendation for fat, in particular, should not be applied in full to the diets of pre-school children especially where appetite is poor.
Table 3. Dietary reference values for macronutrients, for the population in general, i.e. all ages (% food energy)
|Source: DH 1991.|
|of which saturates||11|
|of which starch, intrinsic sugars and milk sugars||39|
|of which NMES*||11|
There are no specific UK figures for the desirable amount of dietary fibre (non-starch polysaccharide, NSP) for children. The Department of Health recommends that children should have proportionally lower fibre intakes than adults; the current UK DRV for adults is 18 g of NSP per day as measured by the Englyst method (DH 1991). This equates to approximately 24 g if the Association of Official Analytical Chemists (AOAC) method is used (Lunn & Buttriss 2007).
SACN is currently reviewing the scientific evidence and associated dietary recommendations for fibre (as well as for carbohydrates in general); a report is expected in 2014. Meanwhile, the European Food Safety Authority (EFSA) has defined fibre as non-digestible carbohydrates (including NSP, resistant oligosaccharides, resistant starch) plus lignin (EFSA 2007, 2010a). This definition is in accordance with methods of analysis approved by the AOAC. EFSA's definition of fibre has been adopted by the European Commission as the basis of fibre declarations on food packaging in Europe (EC 2008). EFSA's recommended intake level for adults is 25 g per day. For children EFSA suggests that ‘dietary fibre intake of 2 g per MJ should be adequate for normal laxation in children, based on the dietary fibre intake that is considered adequate for normal laxation in adults (25 g, equivalent to 2 to 3 g per MJ for daily energy intakes of 8 to 12 MJ) and taking into account that energy intake relative to body size in children is higher than in adults’ (EFSA 2010a).
For most essential nutrients, current UK requirements for children have been estimated by extrapolating published data for infants and adults, as little specific information for school-aged children existed when the DRVs were developed (DH 1991). During adolescence, most DRVs are set higher for boys than for girls because of their increased rates of growth, bone synthesis and bone mineralisation but the DRV for iron intake in post-pubertal girls is higher than for boys, to take account of blood lost during menstruation. However, discrepancies between iron intake data and iron status data (see section ‘Findings of the National Diet and Nutrition Survey’) have led to discussions around whether the iron intake recommendations may be set higher than necessary; some experts have suggested reassessing the DRVs for iron when more, good-quality dose–response data becomes available (SACN 2010).
High sodium intake in children, as well as in adults, has been associated with increased risk of high blood pressure and, in 2003, SACN established target average salt intakes for adults and children (Table 4), which are upper intake levels (SACN 2003). See sections ‘Findings of the National Diet and Nutrition Survey’ and ‘Food provision in school’ for details on salt intakes in schoolchildren.
Table 4. Target average salt intake in children aged 4–18 years
|Age (years)||Salt (g/day)||Sodium equivalents (g/day)|
|Source: SACN 2003.|
Vitamin D supplements (in the form of vitamin drops also containing vitamins A and C) are recommended for children under the age of 5 years. For schoolchildren, there are currently no recommendations for dietary vitamin D intakes as it has been expected that most people, with the exception of very young children, pregnant and breastfeeding women, and elderly people, obtain an adequate amount of the vitamin via the action of sunlight on the skin. However, it has become apparent that a substantial proportion of children (and adults) have low vitamin D status (see sections ‘Findings of the National Diet and Nutrition Survey’ and ‘Bone health’) and vitamin D recommendations are currently being reviewed by a SACN working group (www.sacn.gov.uk).
Various factors affect an individual's ability to produce vitamin D, including latitude, pigmentation of skin and style of dress. Solar ultraviolet (UV) radiation, which is required for the production of vitamin D in the skin, varies with latitude and time of year. From mid-October to the beginning of April, UV radiation in the UK is not strong enough to stimulate vitamin D synthesis, which means the body has to rely on dietary vitamin D and body stores. This situation is exacerbated in people with darker skin (as discussed later) and in general leads to lower blood vitamin D levels during winter and early spring (lowest in January to March) compared with summer and early autumn (highest in July to September). As a result, prevalence of low vitamin D status is generally higher during January to March (SACN 2007). Darker skinned people living in the UK, in particular those who have limited sun exposure because of their lifestyle or style of dress, may not achieve an adequate vitamin D status. Findings from a recent study suggest that children from ethnic minorities living in England also have lower dietary vitamin D intakes, further aggravating the situation. In particular, South Asian children had significantly lower vitamin D intakes compared with White European children, and intakes of Black African-Caribbean children were also lower (Donin et al. 2010). For more than two decades, the Department of Health has recommended that Asian children continue taking vitamin D supplements (10 μg/d) after the age of 5 years, particularly where religion and customs dictate that their skin is kept covered when outside, resulting in limited exposure of their darker skin to the relatively weak sunlight available in the UK (DH 1991), but communication of this message seems to have been limited and is now being reemphasised (along with advice about supplementation for other vulnerable groups).