Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
1 Introduction to Dietary Reference Intakes Dietary Reference Intakes (DRIs) comprise a set of nutrient-based reference values, each of which has special uses. The development of DRIs expands on the periodic reports, Recommended Dietary Allow- ances, which have been published since 1941 by the National Acade- my of Sciences and the Recommended Nutrient Intakes of Canada. This comprehensive effort is being undertaken by the Standing Commit- tee on the Scientific Evaluation of Dietary Reference Intakes of the Food and Nutrition Board, Institute of Medicine, National Acade- mies, with the active involvement of Health Canada. See Appendix A for a description of the overall process and its origins. WHAT ARE DIETARY REFERENCE INTAKES? The reference values, collectively called the Dietary Reference In- takes (DRIs), include the Estimated Average Requirement (EAR), Recommended Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake Level (UL). A requirement is defined as the lowest continuing intake level of a nutrient that will maintain a defined level of nutriture in an indi- vidual. The chosen criterion of nutritional adequacy is identified in each chapter; note that the criterion may differ for individuals at different life stages. Hence, particular attention is given throughout this report to the choice and justification of the criterion used to establish requirement values. This approach differs somewhat from that used by the World Health Organization, Food and Agriculture Organization, and Inter- 29
30 DIETARY REFERENCE INTAKES national Atomic Energy Agency (WHO/FAO/IAEA) Expert Con- sultation on Trace Elements in Human Nutrition and Health (WHO, 1996). That publication uses the term basal requirement to indicate the level of intake needed to prevent pathologically relevant and clinically detectable signs of a dietary inadequacy. The term norma- tive requirement indicates the level of intake sufficient to maintain a desirable body store or reserve. In developing RDAs and AIs, em- phasis is placed instead on the reasons underlying the choice of the criterion of nutritional adequacy used to establish the requirement. They have not been designated as basal or normative. Unless otherwise stated, all values given for EARs, RDAs, and AIs represent the quantity of the nutrient or food component to be supplied by foods from a diet similar to those consumed in Canada and the United States. If the food source of a nutrient is very differ- ent (as in diets of some ethnic groups) or if the source is supple- ments, adjustments may have to be made for differences in nutrient bioavailability. When this is an issue, it is discussed for the specific nutrient in the section âSpecial Considerationsâ. RDAs and AIs are levels of intake recommended for individuals. They should reduce the risk of developing a condition that is associ- ated with the nutrient in question and that has a negative functional outcome. The DRIs apply to the apparently healthy general popula- tion. Meeting the recommended intakes for the nutrients would not necessarily provide enough for individuals who are already mal- nourished, nor would they be adequate for certain disease states marked by increased nutritional requirements. Qualified medical and nutrition personnel must tailor recommendations for individu- als who are known to have diseases that greatly increase nutritional requirements or who are at risk for developing adverse effects asso- ciated with higher intakes. Although the RDA or AI may serve as the basis for such guidance, qualified personnel should make necessary adaptations for specific situations CATEGORIES OF DIETARY REFERENCE INTAKES Each type of Dietary Reference Intake (DRI) refers to average daily nutrient intake of individuals over time. In most cases, the amount taken from day to day may vary substantially without ill effect. Recommended Dietary Allowance The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient require-
INTRODUCTION 31 EAR R isk o f Adverse Effects R isk o f In a de q u a cy RDA UL 1.0 0 .5 0 .5 0 0 O b se rve d Leve l of Intake FIGURE 1-1 Dietary reference intakes. This figure shows that the Estimated Aver- age Requirement (EAR) is the intake at which the risk of inadequacy is 0.5 (50 percent) to an individual. The Recommended Dietary Allowance (RDA) is the intake at which the risk of inadequacy is very smallâonly 0.02 to 0.03 (2 to 3 percent). The Adequate Intake (AI) does not bear a consistent relationship to the EAR or the RDA because it is set without being able to estimate the requirement. At intakes between the RDA and the Tolerable Upper Intake Level (UL), the risks of inadequacy and of excess are both close to 0. At intakes above the UL, the risk of adverse effects may increase. ment of nearly all (97 to 98 percent) healthy individuals in a partic- ular life stage and gender group (see Figure 1-1). The RDA is in- tended to be used as a goal for daily intake by individuals. The process for setting the RDA is described below; it usually depends on being able to set an Estimated Average Requirement (EAR). That is, if an EAR cannot be set, no RDA will be set. Estimated Average Requirement1 The Estimated Average Requirement (EAR) is the daily intake value that is estimated to meet the requirement, as defined by the speci- fied indicator or criterion of adequacy, in half of the apparently healthy individuals in a life stage or gender group (see Figure 1-1). A normal or symmetrical distribution (median and mean are simi- 1 The definition of EAR implies a median as opposed to a mean, or average. The median and average would be the same if the distribution of requirements followed a symmetrical distribution and would diverge as a distribution became skewed.
32 DIETARY REFERENCE INTAKES lar) is usually assumed for nutrient requirements. At this level of intake, the other half of a specified group would not have its nutri- tional needs met. The general method used to set the EAR is the same for all the nutrients. The specific approaches, which are pro- vided in Chapters 4 through 12, differ because of the different types of data available. For many of the nutrients, there are few direct data on the requirements of children. Thus, EARs and RDAs for children are based on extrapolations from adult values. The method is described in Chapter 2. Method for Setting the RDA when Nutrient Requirements Are Normally Distributed If the requirement for the nutrient is normally distributed, and the standard deviation (SD) of the EAR is available, the RDA is defined as equal to the EAR plus 2 SDs of the EAR: RDA = EAR + 2 SDEAR. If data about variability in requirements are insufficient to calcu- late an SD, a coefficient of variation (CVEAR) of 10 percent will be ordinarily assumed and used to estimate the SD: CVEAR = SDEAR/EAR and SD = (EAR Ã CVEAR); the resulting equation for the RDA is RDA = EAR + 2 (0.1 Ã EAR) or RDA = 1.2 Ã EAR. The assumption of a 10 percent CV is based on extensive data on the variation in basal metabolic rate (FAO/WHO/UNA, 1985; Garby and Lammert, 1984), which contributes about two-thirds of the daily energy needs of many individuals residing in Canada and the United States (Elia, 1992) and on the similar CV of 12.5 percent estimated for the protein requirements in adults (FAO/WHO/
INTRODUCTION 33 UNA, 1985). If data are not available for estimation of a standard deviation, then a CV of 10 percent is assumed depending on the information that is available. Method for Setting the RDA when Nutrient Requirements Are Not Normally Distributed When factorial modeling is used to estimate the distribution of requirements from the distributions of the individual components of requirement (e.g., losses, accretion), it is necessary to add the individual distributions. For normal component distributions, this is straightforward since the resultant distribution is also normal, with a mean that is the sum of component means and a variance (the square of the SD) that is the sum of the individual variances. The ninety-seven and one-half percentile is then estimated as the mean value plus two SDs. If the requirement of a nutrient is not normally distributed but can be transformed to normality, its EAR and RDA can be estimated by transforming the data, calculating a fiftieth and a ninety-seventh and one-half percentile, and transforming these percentiles back into the original units. In this case, the difference between the EAR and the RDA cannot be used to obtain an estimate of the CV be- cause skewing is usually present. If normality cannot be assumed for all of the components of re- quirement, then Monte Carlo simulation is used for the summation of the components. This approach involves simulation of a large population of individuals (e.g., 100,000) each with his or her own requirement for a particular nutrient. To accomplish this, the com- ponent parts of nutrient needs (the factorial components) are treat- ed as coming from independent random distributions. Using iron as an example (see Chapter 9), for basal iron loss, a distribution of expected losses was generated. For each individual in the simulated population, a randomly selected iron loss value was drawn from that distribution of iron losses. This is done for each component of iron need and then these components were summed for each individual yielding the simulated iron needs. The total requirement is then calculated for each individual and the median and the ninety-seven and one-half percentile calculated directly. Information about the distribution of values for the requirement components is modeled on the basis of known physiology. Monte Carlo approaches may be used in the simulation of the distribution of components; or, where large data sets exist for similar popula- tions (such as growth rates in infants), estimates of relative variability
34 DIETARY REFERENCE INTAKES may be transferred to the component in the simulated population (Gentle, 1998). At each step, the goal is to achieve distribution values for the component that not only reflect known physiology or known direct observations, but also values that can be transformed into a distribution that can be modeled and used in selecting ran- dom members to contribute to the final requirement distribution. When the final distribution representing the convolution of com- ponents has been derived, then the median and ninety-seven and one-half percentile of the distribution can be directly estimated. It is recognized that in its simplest form, the Monte Carlo approach ignores possible correlation among components. In the case of iron, however, expected correlation is built into the modeling of the re- quirement where components are linked to a common variable, such as growth rate, so that not all sources of correlation are neglected. Other Uses of the EAR The EAR may also be used in the assessment of the intake of groups (IOM, 2000) or, together with an estimate of the variance of intake, be used in planning for the intake of groups (Beaton, 1994) (see Chapter 14). Adequate Intake If sufficient scientific evidence is not available to calculate an EAR, a reference intake called an Adequate Intake (AI) is provided instead of an RDA. The AI is a value based on experimentally derived intake levels or approximations of observed mean nutrient intakes by a group (or groups) of healthy people. In the judgment of the Stand- ing Committee on the Scientific Evaluation of Dietary Reference Intakes, the AI for children and adults is expected to meet or exceed the amount needed to maintain a defined nutritional state or crite- rion of adequacy in essentially all members of a specific healthy population. Examples of defined nutritional states include normal growth, maintenance of normal circulating nutrient values, or other aspects of nutritional well-being or general health. The AI is set when data are considered to be insufficient or inade- quate to establish an EAR on which an RDA would be based. For example, for young infants for whom human milk is the recom- mended sole source of food for most nutrients for the first 4 to 6 months, the AI is based on the daily mean nutrient intake supplied by human milk for healthy, full-term infants who are exclusively fed human milk. For adults, the AI may be based on data from a single
INTRODUCTION 35 experiment, on estimated dietary intakes in apparently healthy pop- ulation groups (e.g., vitamin K, chromium, or manganese), or on a review of data from different approaches that considered alone do not permit a reasonably confident estimate of an EAR. Similarities Between the AI and the RDA Both the AI and RDA are to be used as a goal for individual intake. In general, the values are intended to cover the needs of nearly all persons in a life stage group. (For infants, the AI is the mean intake when infants in the age group are consuming human milk. Larger infants may have greater needs, which they meet by consuming more milk.) As with RDAs, AIs for children and adoles- cents may be extrapolated from adult values if no other usable data are available. Differences Between the AI and the RDA There is much less certainty about the AI value than about the RDA value. Because AIs depend on a greater degree of judgment than is applied in estimating the EAR and subsequently the RDA, the AI may deviate significantly from and be numerically higher than the RDA. For this reason, AIs must be used with greater care than is the case for RDAs. Also, the RDA is usually calculated from the EAR by using a formula that takes into account the expected variation in the requirement for the nutrient (see previous section, âEstimated Average Requirementâ). Tolerable Upper Intake Level The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the specified life stage group (see Fig- ure 1-1). As intake increases above the UL, the potential risk of adverse effects may increase. The term tolerable intake was chosen to avoid implying a possible beneficial effect. Instead, the term is in- tended to connote a level of intake that can, with high probability, be tolerated biologically. The UL is not intended to be a recom- mended level of intake, and there is no established benefit for healthy individuals if they consume a nutrient in amounts exceed- ing the recommended intake (the RDA or AI). The UL is based on an evaluation conducted by using the meth- odology for risk assessment of nutrients (see Chapter 3). The need
36 DIETARY REFERENCE INTAKES for setting ULs grew out of the increased fortification of foods with nutrients and the use of dietary supplements by more people and in larger doses. The UL applies to chronic daily use. As in the case of applying AIs, professionals should avoid very rigid application of ULs and first assess the characteristics of the individual and group of concern, such as source of nutrient, physiological state of the individual, length of sustained high intakes, and so forth. For some nutrients such as vitamin K, arsenic, chromium, and silicon, data are not sufficient for developing a UL. This indicates the need for caution in consuming amounts greater than the rec- ommended intakes; it does not mean that high intakes pose no risk of adverse effects. The safety of routine, long-term intake above the UL is not well documented. Although members of the general population should be advised not to routinely exceed the UL, intake above the UL may be appropriate for investigation within well-controlled clinical trials. Clinical trials of doses above the UL should not be discour- aged as long as subjects participating in these trials have signed informed consent documents regarding possible toxicity and as long as these trials employ appropriate safe monitoring of trial subjects. Determination of Adequacy In the derivation of the EAR or AI, close attention has been paid to the determination of the most appropriate indicators of adequacy. A key question is, Adequate for what? In many cases, a continuum of benefits may be ascribed to various levels of intake of the same nutrient. One criterion may be deemed the most appropriate to determine the risk that an individual will become deficient in the nutrient whereas another may relate to reducing the risk of chronic degenerative disease, such as diabetes mellitus or osteoporosis. Each EAR and AI is described in terms of the selected criterion. The potential role of the nutrient in the reduction of disease risk was considered in developing the EARs. With the acquisition of additional data relating intake to chronic disease or disability, the choice of the criterion for setting the EAR may change. PARAMETERS FOR DIETARY REFERENCE INTAKES Life Stage Groups The life stage groups described below were chosen by keeping in mind all the nutrients to be reviewed, not only those included in
INTRODUCTION 37 this report. Additional subdivisions within these groups may be added in later reports. If data are too sparse to distinguish differ- ences in requirements by life stage or gender group, the analysis may be presented for a larger grouping. Infancy Infancy covers the period from birth through 12 months of age and is divided into two 6-month intervals. The first 6-month interval was not subdivided further because intake is relatively constant dur- ing this time. That is, as infants grow they ingest more food; how- ever, on a body weight basis their intake remains the same. During the second 6 months of life, growth velocity slows, and thus total daily nutrient needs on a body weight basis may be less than those during the first 6 months of life. For a particular nutrient, the average intake by full-term infants who are born to healthy, well-nourished mothers and exclusively fed human milk has been adopted as the primary basis for deriving the Adequate Intake (AI) for most nutrients during the first 6 months of life. The value used is thus not an Estimated Average Require- ment (EAR); the extent to which intake of human milk may result in exceeding the actual requirements of the infant is not known, and ethics of experimentation preclude testing the levels known to be potentially inadequate. Therefore, the AI is not an EAR in which only half of the group would be expected to have their needs met. Using the infant fed human milk as a model is in keeping with the basis for estimating nutrient allowances of infants developed in the last Recommended Dietary Allowances (RDA) (NRC, 1989) and Recommended Nutrient Intakes (RNI) (Health Canada, 1990) re- ports. It also supports the recommendation that exclusive human milk feeding is the preferred method of feeding for normal full- term infants for the first 4 to 6 months of life. This recommenda- tion has also been made by the Canadian Paediatric Society (Health Canada, 1990), the American Academy of Pediatrics (AAP, 1997) and in the Food and Nutrition Board report Nutrition During Lacta- tion (IOM, 1991). In general, for this report special consideration was not given to possible variations in physiological need during the first month after birth or to the variations in intake of nutrients from human milk that result from differences in milk volume and nutrient concentra- tion during early lactation. Specific Dietary Reference Intakes (DRIs) to meet the needs of formula-fed infants are not proposed in this report. The previously published RDAs and RNIs for infants
38 DIETARY REFERENCE INTAKES have led to much misinterpretation of the adequacy of human milk because of a lack of understanding about their derivation for young infants. Although they were based on human milk composition and volume of intake, the previous RDA and RNI values allowed for lower bioavailability of nutrients from nonhuman milk. Ages 0 through 6 Months. To derive the AI value for infants ages 0 through 6 months, the mean intake of a nutrient was calculated on the basis of the average concentration of the nutrient from 2 through 6 months of lactation with use of consensus values from several reported studies (Atkinson et al., 1995), and an average vol- ume of milk intake of 0.78 L/day as reported from studies of full- term infants by test weighing, a procedure in which the infant is weighed before and after each feeding (Butte et al., 1984; Chandra, 1984; Hofvander et al., 1982; Neville et al., 1988). Because there is variation in both of these measures, the computed value represents the mean. It is expected that infants will consume increased vol- umes of human milk as they grow. Ages 7 through 12 Months. Except for iron and zinc, which have relatively high requirements, there is no evidence for markedly dif- ferent nutrient needs during the period of infantsâ growth accelera- tion and gradual weaning to a mixed diet of human milk and solid foods from ages 7 through 12 months. The basis of the AI values derived for this age category was the sum of the specific nutrient provided by 0.6 L/day of human milk, which is the average volume of milk reported from studies in this age category (Heinig et al., 1993), and that provided by the usual intakes of complementary weaning foods consumed by infants in this age category (Specker et al., 1997). This approach is in keeping with the current recommen- dations of the Canadian Paediatric Society (Health Canada, 1990), the American Academy of Pediatrics (AAP, 1997), and Nutrition Dur- ing Lactation (IOM, 1991) for continued feeding of human milk to infants through 9 to 12 months of age with appropriate introduc- tion of solid foods. One problem encountered in trying to derive intake data in in- fants was the lack of available data on total nutrient intake from a combination of human milk and solid foods in the second 6 months of life. Most intake survey data do not identify the milk source, but the published values indicate that cow milk and cow milk formula were most likely consumed.
INTRODUCTION 39 Toddlers: Ages 1 through 3 Years The greater velocity of growth in height during ages 1 through 3 years compared with ages 4 through 5 years provides a biological basis for dividing this period of life. Because children in the United States and Canada from age 4 years onwards begin to enter the public school system, ending this life stage prior to age 4 years seemed appropriate. Data are sparse for indicators of nutrient ade- quacy on which to derive DRIs for these early years of life. In some cases, DRIs for this age group were derived from data extrapolated from studies of infants or of adults aged 19 years and older. Early Childhood: Ages 4 through 8 Years Because major biological changes in velocity of growth and chang- ing endocrine status occur during ages 4 through 8 or 9 years (the latter depending on onset of puberty in each gender), the category of 4 through 8 years is appropriate. For many nutrients, a reason- able amount of data is available on nutrient intake and various criteria for adequacy (such as nutrient balance measured in young children ages 5 through 7 years) that can be used as the basis for the EARs and AIs for this life stage group. Puberty/Adolescence: Ages 9 through 13 Years and 14 through 18 Years Because current data support younger ages for pubertal develop- ment, it was determined that the adolescent age group should begin at 9 years. The mean age of onset of breast development (Tanner Stage 2) for white females in the United States is 10.0 Â± 1.8 (stan- dard deviation) years; this is a physical marker for the beginning of increased estrogen secretion (Herman-Giddens et al., 1997). In African-American females, onset of breast development is earlier (mean 8.9 years Â± 1.9). The reason for the observed racial differences in the age at which girls enter puberty is unknown. The onset of the growth spurt in girls begins before the onset of breast development (Tanner, 1990). The age group of 9 through 13 years allows for this early growth spurt of females. For males, the mean age of initiation of testicular development is 10.5 to 11 years, and their growth spurt begins 2 years later (Tanner, 1990). Thus, to begin the second age category at 14 years and to have different EARs and AIs for females and males for some nutri- ents at this age seems biologically appropriate. All children continue
40 DIETARY REFERENCE INTAKES to grow to some extent until as late as age 20 years; therefore, having these two age categories span the period 9 through 18 years of age seems justified. Young Adulthood and Middle Ages: Ages 19 through 30 Years and 31 through 50 Years The recognition of the possible value of higher nutrient intakes during early adulthood on achieving optimal genetic potential for peak bone mass was the reason for dividing adulthood into ages 19 through 30 years and 31 through 50 years. Moreover, mean energy expenditure decreases during this 30-year period, and needs for nutrients related to energy metabolism may also decrease. For some nutrients, the DRIs may be the same for the two age groups. How- ever, for other nutrients, especially those related to energy metabo- lism, EARs (and RDAs) are likely to differ for these two age groups. Adulthood and Older Adults: Ages 51 through 70 Years and Over 70 Years The age period of 51 through 70 years spans active work years for most adults. After age 70 years, people of the same age increasingly display variability in physiological functioning and physical activity. A comparison of people over age 70 years who are the same chrono- logical age may demonstrate as much as a 15- to 20-year age-related difference in level of reserve capacity and functioning. This is dem- onstrated by age-related declines in nutrient absorption and renal function. Because of the high variability in functional capacity of older adults, the EARs and AIs for this age group may reflect a greater variability in requirements for the older age categories. This variability may be most applicable to nutrients for which require- ments are related to energy expenditure. Pregnancy and Lactation Recommendations for pregnancy and lactation may be subdivided because of the many physiological changes and changes in nutrient needs that occur during these life stages. In setting EARs and AIs for these life stages, however, consideration is given to adaptations to increased nutrient demand, such as increased absorption and greater conservation of many nutrients. Moreover, nutrients may undergo net losses due to physiological mechanisms regardless of the nutrient intake. Thus, for some nutrients, there may not be a
INTRODUCTION 41 basis for EAR values that are different during these life stages than they are for other women of comparable age. Reference Weights and Heights The reference weights and heights selected for children and adults are shown in Table 1-1. The values are based on anthropo- metric data collected from 1988â1994 as part of the Third National Health and Nutrition Examination Survey (NHANES III) in the United States. When extrapolation to a different age group was conducted, these reference weights were used, except for iron which used weights with known coefficients of variation that were required for factorial modeling. Using NHANES III data, the median heights for the life stage and gender groups through age 30 years were identified, and the median weights for these heights were based on reported median Body Mass Index (BMI) for the same individuals. Since there is no evidence that weight should change as adults age if activity is main- tained, the reference weights for adults ages 19 through 30 years are applied to all adult age groups. The most recent nationally representative data available for Cana- dians (from the l970â1972 Nutrition Canada Survey [Demirjian, 1980]) were reviewed. In general, median heights of children from TABLE 1-1 Reference Heights and Weights for Children and Adults in the United Statesa Median Body Reference Reference Mass Index Height, Weightb Gender Age (kg/m2) cm (in) kg (lb) Male, female 2â6 mo â 64 (25) 7 (16) 7â11 mo â 72 (28) 9 (20) 1â3 y â 91 (36) 13 (29) 4â8 y 15.8 118 (46) 22 (48) Male 9â13 y 18.5 147 (58) 40 (88) 14â18 y 21.3 174 (68) 64 (142) 19â30 y 24.4 176 (69) 76 (166) Female 9â13 y 18.3 148 (58) 40 (88) 14â18 y 21.3 163 (64) 57 (125) 19â30 y 22.8 163 (64) 61 (133) a Adapted from the Third National Health and Nutrition Examination Survey (NHANES III), 1988â1994. b Calculated from body mass index and height for ages 4 through 8 years and older.
42 DIETARY REFERENCE INTAKES 1 year of age in the United States were greater by 3 to 8 cm (1 to 3 inches) than those of children of the same age in Canada measured two decades earlier (Demirjian, 1980). This difference could be partly explained by approximations necessary to compare the two data sets but more likely by a continuation of the secular trend of increased heights for age noted in the Nutrition Canada Survey when it compared data from that survey with an earlier (1953) national Canadian survey (Pett and Ogilvie, 1956). Similarly, median weights beyond age 1 year derived from the recent survey in the United States (NHANES III) were also greater than those obtained from the older Canadian survey (Demirjian, 1980). Differences were greatest during adolescence, ranging from 10 to 17 percent higher. The differences probably reflect the secular trend of earlier onset of puberty (Herman-Giddens et al., 1997), rather than differences in populations. Calculations of BMI for young adults (e.g., a median of 22.6 for Canadian women compared with 22.8 for U.S. women) resulted in similar values, thus indicating greater concordance between the two surveys by adulthood. The reference weights chosen for this report were based on the most recent data set available from either country, with recognition that earlier surveys in Canada indicated shorter stature and lower weights during adolescence than did surveys in the United States. Reference weights are used primarily when setting the EAR or Tolerable Upper Intake Level for children or when relating the nutrient needs of adults to body weight. For the 4- to 8-year-old age group, a small 4-year-old child can be assumed to require less than the EAR and that a large 8-year-old child will require more than the EAR. However, the RDA or AI should meet the needs of both. SUMMARY Dietary Reference Intakes (DRIs) is a generic term for a set of nutrient reference values that includes the Estimated Average Requirement, Recommended Dietary Allowance, Adequate Intake, and Tolerable Upper Intake Level. These reference values are being developed for life stage and gender groups in a joint U.S. and Canadian activity. This report, which is one volume in a series, covers the DRIs for vitamins A and K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. REFERENCES AAP (American Academy of Pediatrics). 1997. Breastfeeding and the use of human milk. Pediatrics 100:1035â1039.
INTRODUCTION 43 Atkinson SA, Alston-Mills BP, Lonnerdal B, Neville MC, Thompson MP. 1995. Major minerals and ionic constituents of human and bovine milk. In: Jensen RJ, ed. Handbook of Milk Composition. California: Academic Press. Pp. 593â619. Beaton GH. 1994. Criteria of an adequate diet. In: Shils ME, Olson JA, Shike M, eds. Modern Nutrition in Health and Disease, 8th ed. Philadelphia: Lea & Febiger. Pp. 1491â1505. Butte NF, Garza C, Smith EO, Nichols BL. 1984. Human milk intake and growth in exclusively breast-fed infants. J Pediatr 104:187â195. Chandra RK. 1984. Physical growth of exclusively breast-fed infants. Nutr Res 2:275â 276. Demirjian A. 1980. Anthropometry Report. Height, Weight, and Body Dimensions: A Re- port from Nutrition Canada. Ottawa: Minister of National Health and Welfare, Health and Promotion Directorate, Health Services and Promotion Branch. Elia M. 1992. Energy expenditure and the whole body. In: Kinney JM, Tucker HN, eds. Energy Metabolism: Tissue Determinants and Cellular Corollaries. New York: Raven Press. Pp. 19â59. FAO/WHO/UNA (Food and Agriculture Organization of the United Nations/ World Health Organization/United Nations Association). 1985. Energy and Protein Requirements Report of a Joint FAO/WHO/UNA Expert Consultation. Tech- nical Report Series, No. 724. Geneva: WHO. Garby L, Lammert O. 1984. Within-subjects between-days-and-weeks variation in energy expenditure at rest. Hum Nutr Clin Nutr 38:395â397. Gentle JE. 1998. Random Number Generation and Monte Carlo Methods. New York: Springer-Verlag. Health Canada. 1990. Nutrition Recommendations. The Report of the Scientific Review Committee 1990. Ottawa: Canadian Government Publishing Centre. Heinig MJ, Nommsen LA, Peerson JM, Lonnerdal B, Dewey KG. 1993. Energy and protein intakes of breast-fed and formula-fed infants during the first year of life and their association with growth velocity: The DARLING Study. Am J Clin Nutr 58:152â161. Herman-Giddens ME, Slora EJ, Wasserman RC, Bourdony CJ, Bhapkar MV, Koch GG, Hasemeier CM. 1997. Secondary sexual characteristics and menses in young girls seen in office practice: A study from the Pediatric Research in Office Settings network. Pediatrics 99:505â512. Hofvander Y, Hagman U, Hillervik C, Sjolin S. 1982. The amount of milk consumed by 1â3 months old breast- or bottle-fed infants. Acta Paediatr Scand 71:953â958. IOM (Institute of Medicine). 1991. Nutrition During Lactation. Washington, DC: National Academy Press. IOM 2000. Dietary Reference Intakes: Applications in Dietary Assessment. Washington, DC: National Academy Press. Neville MC, Keller R, Seacat J, Lutes V, Neifert M, Casey C, Allen J, Archer P. 1988. Studies in human lactation: Milk volumes in lactating women during the onset of lactation and full lactation. Am J Clin Nutr 48:1375â1386. NRC (National Research Council). 1989. Recommended Dietary Allowances, 10th ed. Washington, DC: National Academy Press. Pett LB, Ogilvie GH. 1956. The Canadian Weight-Height Survey. Hum Biol 28:177â 188. Specker BL, Beck A, Kalkwarf H, Ho M. 1997. Randomized trial of varying mineral intake on total body bone mineral accretion during the first year of life. Pediatrics 99:E12. Tanner JM. 1990. Growth at Adolescence. Oxford: Oxford University Press. WHO (World Health Organization). 1996. Trace Elements in Human Nutrition and Health. Geneva: WHO.