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Growth and Micronutrient Needs of Adolescents

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Growth and Micronutrient Needs of Adolescents European Journal of Clinical Nutrition (2000) 54, Suppl 1, S11±S15 ß 2000 Macmillan Publishers Ltd All rights reserved 0954±3007/00 $15.00 www.nature.com/ejcn Growth and micronutrient needs of adolescents B Olmedilla* and F Granado Servicio de NutricioÂn, Unidad de Vitaminas, ClõÂnica Puerta de Hierro, 28035-Madrid, Spain Objective: This paper focuses on micronutrients in relation to needs throughout adolescence, a period which involved growth and development that occur through a complex interaction of genetic instructions, hormones and environmental in¯uences, many of them of dietary origin. In the context of micronutrient `needs' it is of special importance to differentiate between the `nutritional needs' and `metabolic needs'. Two main questions arise in relation to the micronutrient needs: (1) why are micronutrients necessary? and (2) how are their needs assessed? Results: The `necessary' amount will differ according to the objectives pursued: (a) to achieve a satisfactory rate of growth and development; and (b) to maintain `optimal health'. The assesment of micronutrient needs and status has proved to be dif®cult, but when elucidating and establishing them, it is imperative to arrive at the estimates in the light of their interdependent role in metabolism and functions. The knowledge of micronutrient metabolic needs can be approached through epidemiological observations, bioavailability studies and clinical trials. However, there is a nearly total absence of reports on the particular metabolic and dietary needs of adolescents. Conclusion: Thus more studies are required in relation to the effect of features associated with adolescence on `needs', evaluating their impact on bioavailablility and turnover (storage and losses), and the interactions among micronutrients in the assessment of metabolic and nutritional needs. Another aim should be to establish static and functional indexes, reference values and cut-off points in adolescence, to be used in clinical and epidemiological studies. Future studies should focus on needs to determine those required to maintain `optimal functions' and regarding the potential prevention of chronic adult diseases. Descriptors: micronutrient needs; adolescence; metabolic needs; nutritional needs; growth European Journal of Clinical Nutrition (2000) 54, Suppl 1, S11±S15 Introduction `needs' and `requirements', which are often used indis- tinctly. We have a great deal more information on the The micronutrients are a group of dietary constituents micronutrient `requirements' in terms of `nutritional characterized by the low amounts in which they are needs', that is, the amount of a nutrient that must be found in the diet, but which nevertheless are the key to supplied in the diet in order to satisfy the `metabolic optimal macronutrient metabolism, and by the interdepen- need'. The concept that is crucial between the two is dent role of many of them in metabolism and functions. bioavailability, meaning the fraction of the ingested nutri- Micronutrients are essential for growth and development, ent that is utilized or stored for normal physiological utilization of macronutrients, maintenance of adequate functions. defences against infectious diseases and for many other In general, the amounts of micronutrients considered as metabolic and physiological functions (WHO, 1996). `needs' are lower than those estimated as requirements The micronutrients classically considered as essential which, in turn, are lower than the recommendations, espe- comprise just 13 vitamins and around 16 minerals, although cially when we refer to cationic minerals and fat-soluble our diet includes a multitude of other compounds, some of vitamins. which most likely, but not de®nitely, are responsible for actions that are bene®cial to the human body. In this paper we will focus on the micronutrients in Needs: why are micronutrients necessary? relation to the needs throughout adolescence, a period which involves growth and development that occur through This is the ®rst point that must be addressed before any a complex interaction of genetic instructions, hormones and evaluation of the needs for a given nutrient, since the environmental in¯uences, most of them of dietary origin `necessary' amount will differ according to the objectives (Lachance, 1998a). This `dietary origin' is also linked to pursued, which will depend on what it is known about the third key word of this communication: nutrient needs. micronutrient functions and metabolism in the human body In the context of micronutrients, it is of special importance (Figure 1). Therefore, two general aims can be expressed as to keep in mind the difference between the two words follows: (a) to achieve a satisfactory rate of growth and development (the basic aim); and (b) to maintain `optimal health'. *Correspondence: B. Olmedilla, Clinica de Puerta de Hierro, Servicio de The ®rst aim is related to metabolic needs and efforts to NutricioÂn, c/San Martin de Porres 4, E-28035 Madrid, Spain. avoid de®ciency. However, on compiling information from E-mail: [email protected] Guarantor: B. Olmedilla. the literature, it is surprising how scanty the data upon Contributors: BO: responsibility for the planning and writing of the which the recommendations (`nutritional needs') for ado- manuscript. FG: advice and bibliography search for the manuscript. lescent nutrient `needs' are based and the fact that they are Growth and micronutrient needs of adolescents B Olmedilla and F Granado S12 and osteoporosis prevention, certain micronutrients or non-nutrients (carotenoids, vitamins E and C, etc.) with roles in preventing some chronic and degenerative diseases (certain cancers, cardiovascular disease, macular disease) by means of mechanisms such as antioxidant activity, regulation of expression of key genes, etc., and those involved in enhancing the immune system (to reach `opti- mum' performance) (Weaver, 1992; Berdanier, 1996; WCRF=AICR, 1997). Other examples of micronutrients linked to health and diseases in a nontraditional fashion are those related to anemia (Fe, folic acid, vitamins B-12, B-6 and A, Cu, Co, Figure 1 Micronutrient needs are different according to the objectives Mg and Zn), birth defects (vitamin A, folate), cancer pursued. (vitamins E and C, folate, carotenoids, Fe), central nervous system function (Fe, I, Se, Zn), cognitive function (Fe, Zn, usually obtained by interpolating or extrapolating data vitamins B-1 and B-12), gene interactions (Fe, Zn, vitamins collected in adults and children, rather than basing them B-6, C and K), heart disease (vitamins E, C, B-6 and B-12, on actual experimental evidence (Dwyer, 1981, 1996; carotenoids, folic acid and Fe), immune system develop- RDA, 1989). First, the assumption is accepted that, after ment and host defence (Zn and vitamin E) and osteoporosis infancy, micronutrients are needed in increasing amounts in (Ca, vitamins D and K). proportion to energy requirements for metabolic demands of growth, until the levels recommended for adults are Needs: how are they assessed? reached. Second, nutritional needs or `requirements' are established by evaluating dietary micronutrient intakes and Assessment of micronutrient needs and status has proved comparing them with the `recommendations' made by dif®cult. These estimates must be elucidated and estab- different scienti®c organisms to determine whether or not lished in the light of their interdependent role in metabo- these recommendations are met. Finally, when we actually lism and functions. Metabolic steps require the concomitant ®nd information on the needs (metabolic needs), these are involvement of one or more vitamins and minerals and, as a investigated generally in relation to special situations such general consequence, the interactions among the micronu- as pregnancy, the practice of sports, certain diseases, etc., trients as well as other food components (nutrient and non- but not in apparently healthy adolescents who need, for nutrient) are of great importance and may occur at different tissue growth, an amount equal to the rate of accretion plus levels (Figure 2). the content of newly formed tissue. Especially during the second decade of life, nutrient The second objective, to maintain `optimal health', is requirements (nutritional needs) and metabolic needs are pursued by growing numbers of researchers whose aim is to more closely associated with physiological than chrono- achieve the maximum development of physical and psy- logical age; thus, it is useful to consider this decade as chological aptitudes. From this perspective, not only the consisting of two periods, pubescence and adolescence, `classical' functions but also the newer roles ascribed to since these needs are affected by growth and the resulting several micronutrients, as well as the saturation of body changes from sex hormone secretion. stores, should probably be considered. In the context of The knowledge of micronutrient metabolic needs, which adolescence, this aim would involve the creation and in general are considered to be met if normal functions, veri®cation of dietary regimens that include `proper atti- health and body weight are maintained and depletion tudes' to carry on into adulthood, rather than sporadic prevented, can be approached through epidemiological supplementation of the diet with certain micronutrients, observations, bioavailability studies and clinical trials given that `inappropriate micronutrient intakes' over long involving supplementation. periods of time are considered
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