Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

Minerals

As in the case of vitamins, this document considers only those minerals whose dietary intakes represent a real or potential nutrition problem in Latin America. These are iron, zinc, iodine, fluorine, sodium, and calcium. There are other trace elements known to be biologically needed, such as potassium, copper, selenium, magnesium, molybdenum, manganese, cobalt, and chromium. However, there have been no reported public health problems related to the deficiency or excess intake of any of these in Latin America, and there are no studies about their supply in the usual Latin American diets.

For most of the minerals the recommendations for daily intake are calculated per 1,000 kcal of the diet. The justifications for this are given in the introduction to the section on vitamins. Because the recommendations for iodine are very small and less dependent on the individual's age and energy intake, they are expressed as a total intake per day. In the case of sodium, the only quantitative recommendation made is the maximum limit of daily intake, independent of the total energy intake.

Iron

Iron forms a part of molecules such as haemoglobin and myoglobin, and acts as a coenzyme in many reactions in the organism, especially in oxidation reduction reactions. The majority of the body's iron is in the circulating haemoglobin and reserves in certain organs.

Needs

Iron needs vary with the individual's age, sex, physiological condition, and body reserves of iron. It is also necessary to consider the bioavailability of the iron in the diet and its intestinal absorption, which varies with the individual's iron nutritional status.

A newborn infant has considerable iron in its circulating erythrocytes, and during the first months of life the iron in reserve grows at the expense of circulating haemoglobin. During the first four to six months of life, nursing children fulfil their iron requirements from their body reserves and breast milk; although the concentration of iron in the latter is low, it is absorbed to a high degree. The reserves disappear between four and six months of age, and the diet must then begin to supply sufficient quantities of the mineral in order to prevent anaemia.

Because of their growth, children need a diet proportionally higher in iron than adults; this need is accentuated during puberty. With menarche, women begin to lose blood periodically. During each menstrual period, an average of 25-30 ml of blood are lost, equivalent to 10-15 mg of iron, but some women lose more than 80 ml. This produces an increase in the quantity of iron that the diet must supply.

The need for iron increases by a total of approximately 800 mg during the entire course of pregnancy. In well-nourished women with good body reserves of .iron who continue diets that have highly bioavailable iron, this increased need can be satisfactorily met. However, when women begin their pregnancy with little or no iron reserves because of a chronic deficiency of this mineral and continue eating a diet with low iron bioavailability, as occurs in great sectors of the Latin American population, it is not possible to satisfy the iron requirements with only foods in their natural form. Therefore, it is necessary to use foods fortified with iron or to administer pharmacological iron preparations in order to provide 30-60 mg of iron per day.

The decrease in iron because of blood loss during and after childbirth is compensated for in great part by the decrease in the volume of circulating erythrocytes. During lactation, menstruation is suspended and the loss of iron is reduced, but 0.3-0.5 mg of iron per day is excreted with the milk. Because of this, there is an increase in the physiological need for iron during lactation, and the diet should provide about 2-4 mg more iron per day than for the non-lactating woman who is not menstruating or who is postmenopausal.

Food sources

The quantity of iron in foods does not necessarily correspond to the amount absorbed by the human intestine nor to its bioavailability to the organism. For example, while haem iron is 20% to 30% absorbed, the non-haem iron in the majority of grains and legumes is less than 5% absorbed, and while the iron in human milk is 40% to 50% absorbed, that in cow's milk is 10% to 15% absorbed.

In addition, regulating mechanisms exist that cause iron absorption to vary according to the concentration of haemoglobin and body reserves of iron. Therefore, anaemic persons absorb greater proportions than normal persons, and the degree of absorption grows according to the severity of the anaemia.

These factors should be taken into account in interpreting the quality of food sources of iron, instead of considering only the chemical content of iron in the food. This content is relatively great and its bioavailability high in liver and beef; it is found in smaller quantity but also in highly bioavailable form in chicken and seafood. The iron content in grains, legumes, and leafy vegetables is quite variable and its bioavailability is less than that of iron of animal origin.

Iron that contaminates food, derived from dust in the environment, from cooking utensils, or from industrial processing, can represent a relatively high proportion of ingested iron. Unfortunately, there is no appropriate method available to determine how this iron interacts with the iron in foods, what its bioavailability is. and how much it contributes to satisfying the needs of the individual.

Absorption of iron in a mixed allot

The absorption and bioavailability of iron in a mixed diet whose ingredients are consumed in different proportions and in a non-uniform manner at each meal is not known. Besides the differences between haem and non-haem iron, the latter is strongly influenced by various components in the diet. In this way, the absorption of non-haem iron improves in the presence of meat, chicken, fish, seafood, and various organic acids, especially ascorbic acid. In addition, diverse substances such as tannins and other polyphenols, phytates, certain proteins (such as egg yolk), and some food fibres reduce its absorption. Depending on the presence of such enhancing or inhibiting substances, the absorption of iron in a meal can vary from 1% to 30% in persons with a good nutritional state of iron.

An FAO/WHO committee of experts, convened in 1985, whose report has not yet been published, suggested dividing the common diets in different parts of the world into three categories: those with "low," "intermediate," and "high" bioavailability of iron, in which-in persons without adequate reserves of iron but with a normal capacity to absorb and transport it-the average absorption of the mixture of haeminic and non-haeminic iron is about 5%, 10%, and 15% respectively. These diets can be characterized as follows:

Simple and uniform diets based on grains, roots, and tubers with insignificant amounts of meat, fish, or sources of ascorbic acid have a low bioavailability of iron. In these diets foods such as corn, beans, whole wheat, and sorghum predominate and have sub stances that inhibit the absorption of iron. They are common in the poorest socio-economic classes in almost all of Latin America.

Diets with intermediate bioavailability of iron are those that are based principally on grains, roots, and tubers but include some foods of animal origin and sources of ascorbic acid. A diet of low bioavailability can become "intermediate" by augmenting the content of foods that favour the absorption of iron. Similarly, absorption is reduced when diets with high bioavailability are consumed along with inhibitors of iron absorption, such as tea and coffee. This is common in the middle socio-economic class in many countries in the region.

Diets with a high bioavailability of iron are varied and include large and frequent quantities of meat, chicken, fish, or meals rich in ascorbic acid. They are common in countries with high meat consumption and in the upper socio-economic groups of Latin America.

Table 5 shows the quantities of iron that should be supplied by these three categories of diets to prevent anaemia in 95% of the population. This varies depending on whether body reserves of iron are adequate or low. In the latter case, the expected absorption of iron would be about 22.5%,15%, and 7.4% when its bioavailability is high, intermediate, or low respectively. The increase of absorption will permit the gradual improvement of iron reserves.

TABLE 5. Daily iron intake required to prevent anaemia in almost all of the population (mg per 1,000 kcal of dietary energy)

Source: Ref. 9.
a. Very difficult to achieve with usual diet.

TABLE 6. Daily mineral needs

Sources: Refs. 2,3, and 9.

a. H. I, and L indicate diets with high, intermediate, and low bioavailability of dietary iron respectively
b. H and L indicate diets with high and low bioavailahility of dietary zinc respectively.
c. Supplementary amounts.
d. Anaemia is prevented by good iron reserves before pregnancy and a diet with highly available (haem) iron. Otherwise. an iron supplement of 30-60 mg per day is needed during the second and third trimesters.

The FAD/WHO committee also defined "basal requirements" that correspond to an adequate supply of iron in the tissues and the maintenance of all functions that can be detected clinically. To fulfil them, it is estimated that diets should supply about 50% more iron than is indicated in table 5, but, since this cannot be attained in usual diets in many parts of the world, the committee opted to recommend the intake of the quantities in the table.

The iron intake proposed in this document is 4.5. 6.7, or 13.5 mg of iron per 1,000 kcal, depending on its bioavailability in the diet (table 6). It does not seem realistic to reach an average concentration of 13.5 mg iron per 1,000 kcal with diets with low bioavailability, consisting primarily of foods of vegetable origin. However, with a concentration of 9 mg of iron per 1,000 kcal in those diets, one could fulfil the needs of all age groups except for children under one year old, adolescent women, and menstruating and pregnant women. Since large sectors of the Latin American population eat that type of diet and also have an increase in body iron losses due to parasitism and infections, the fortification of some food vehicle is probably required for those sectors in order to satisfy their iron needs until the diet and the hygienic situation that produces infections are improved.

Zinc

In recent years a great interest has been awakened in the role of zinc as an essential element for humans and animals. Foods of animal origin represent the major dietary source of zinc, followed by cereals and grains, certain tubers and vegetables, and water.

The minimum amounts of zinc needed to maintain health and optimum growth are not well known, nor are there practical methods for the diagnosis of subclinical deficiencies. In Latin American populations where diet is based on cereals and grains, we should be aware of the possibility that zinc deficiency exists.

The World Health Organization's provisional recommendations [3] were calculated with a factorial approach that can be adjusted to the availability of zinc in the diet. In the case of nursing children, it should be noted that the zinc in human milk is highly bioavailable. If the supply of zinc originating from foods is 20% available, a daily consumption of 6 mg is recommended for children under one year old, 8 mg for preschool and school-age children, 14 mg for adolescents, and 11 mg for adults; during lactation 20 mg daily is recommended. All of these recommendations are fulfilled by an intake of 6 mg of zinc per 1,000 kcal. With diets whose zinc is less bioavailable (about 10%-12%), 10 mg of zinc per 1,000 kcal is recommended (table 6).

Sodium

Sodium is located predominantly in the extracellular spaces where osmotic action is performed. Other important functions are related to the regulation of cellular electrical activity and the response of the cardiovascular system to vasopressor agents.

With the levels of ingestion of sodium chloride of 10-15 µg per day prevalent in a diverse population, 20%-30% of normotensive individuals are sensitive to the effects of sodium on arterial pressure. Above this limit, the proportion grows with increasing salt consumption, although the relation between sodium and hypertension is complex and depends on many other factors. It is recommended that the level of salt ingestion should not exceed 5 µg per day. This will require less salt in cooking foods and abandoning the habit of adding salt to food at mealtimes. The majority of processed foods contain large amounts of salt, and this must be taken into account in their use. The sodium content of such foods should be reduced. This problem is of special importance in the case of foods for lactating women and small children. For the latter, in addition to the harm that it potentially can cause, it contributes to creating the undesirable habit of eating excessive salt.

In conditions of profuse perspiration, salt intake can be greater without harm, but should not exceed 10 µg per day.

Calcium

Calcium is one of the principal constituents of bone. Calcium constitutes 1%-2% of body weight, 99% of it being found in bone tissue. The remaining quantity is required for numerous metabolic processes, including hormonal function, nerve transmission, blood coagulation, muscular contraction, and membrane transport.

The dietary sources of calcium are milk and its derivatives, seafoods, sardines, beans, and some vegetables. In countries that consume corn products treated with calcium in their processing, these are an important source of calcium.

There exists evidence that the adequate accumulation of a dense skeletal mass over a long period of growth plays an important role in preventing or limiting the development of osteoporosis, a disease particularly serious in post-menopausal women. As a consequence, it is necessary to ensure an adequate supply of calcium from a young age.

The mechanisms of adaption to low ingestion of calcium are complex and change with the velocity of growth. Because of this, it is difficult to establish recommendations for a whole population. The conclusions of different committees of experts [3; 10-12] lead us to recommend a daily intake of 500 mg for infants under one year old, 800 mg for children over one year old and adults of both sexes, and 1,200 mg for adolescents of both sexes and pregnant or lactating women. These recommendations are met by family diets that supply 500 mg of calcium per 1,000 kcal, but larger portions of foods rich in calcium are recommended for preschool children and adolescent, pregnant, or lactating women (table 6).

Iodine

Iodine deficiency is a problem endemic to many Latin American countries, due principally to the low iodine content of the water and foods in certain regions. Its most obvious consequence is goitre in persons of all ages. However, iodine deficiency during pregnancy can result in newborns with varying degrees of mental retardation, even cretinism, depending on the severity of the deficiency.

The nutritional recommendations for iodine in industrialized countries are on the order of 40-120 µg per day until 10 years of age and 150 µg per day thereafter. To cover the additional needs of pregnancy and lactation, 50 µg per day should be added. For Latin America a daily intake of iodine on the order of 100-200 µg in regions where there is no endemic goitre and 300-400 µg where this problem exists is a desirable nutritional goal.

The richest sources of iodine are shellfish and marine fish. Its content in plants is quite variable, depending on the iodine concentration in water and soil. The latter fluctuates with rainfall and water currents.

Some processed and canned foods have important quantities of iodine. Their consumption has controlled or reduced the prevalence of deficit imbalances in industrialized countries and in the urban areas of some developing countries. The most practical way of combating iodine deficiency in populations in which this is a public health problem is the fortification of table salt (NaCl) with potassium iodate. The fortification should be made in concentrations that provide 100-200 µg daily. This is achieved with fortification in the range of 30-50 ppm (1: 20,000-1: 30,000). It should be noted that, if salt consumption is reduced in accordance with the recommendations given in this report, it may be necessary to revise the recommended levels of iodine fortification.

In isolated populations in which it is not practical to maintain a programme of salt iodization, massive doses of iodine in the form of iodized oil can be administered intramuscularly at intervals of two to three years. Iodized oil taken orally has been used in some studies with promising results.

Fluorine

Fluorine deficiency is closely related to the appearance of dental caries. When it is consumed in adequate quantities during pre- and posteruptive tooth development, fluoride reduces susceptibility to caries. Because experimental deficiency affects the growth of animals, it is considered an essential nutrient.

Fluorine is found in minuscule amounts in all foods and most natural sources of water. Vegetables, meats, cereals, and fruits contain between 0.2 and 1.5 ppm. The majority of waters contain between 0.05 and 1.5 ppm, although some sources have 3 or more ppm.

There are no international recommendations for its consumption, but the US Food and Nutrition Board has recommended a daily intake of 0.1-1.0 mg for those under one year old, 0.5-2.5 mg for older children, and 1.5-4.0 mg for adults [13]. These consumption levels are satisfied by family diets that provide approximately 0.7-1 mg per 1,000 kcal.

In places where the water is very low in fluorine and the prevalence of dental caries is high, fluoridation of water or table salt is recommended. The desirable concentration of added fluorine will depend on the natural concentration of this element in the water. It should be kept in mind that excess fluorine is damaging. The prolonged intake of more than 2.5 mg per day in young children produces pitted teeth. A daily ingestion of 8 mg or more over several years can produce toxicity that manifests itself in bone changes, periostic hyperostosis, areas of bone absorption, and arthritis.

Other options for combating dental caries associated with a low fluorine intake are the use of fluoridated dentifrices and the topical application of fluoride to the teeth.

Nutritional goals for the family

As was indicated before, the dietary guides should be based on the family unit. Furthermore, it is not practical to recommend the preparation of different foods for different family members, except for children under one year old, elderly people with eating difficulties, or sick people.

In light of this, table 7 presents the quantities and concentrations of energy, nutrients, and fibre the family diet should supply in order to reach the nutritional goals and satisfy the needs of all its members. It excludes children under one year old, who should be fed diets according to their age, with special emphasis on breast milk. Additional quantities for pregnancy and lactation are not included either.

TABLE 7. Nutrient intakes to meet needs of all family members

Energy

Preschool: 0.6-0.8 kcal per millilitre of liquid food; approximately 2 kcal per gram of solid food
Other ages: 1.4-2.5 kcal per gram in total diet

Carbohydrates

150-175 g; to provide 60% - 70% of total energy

Protein

25-30 g ( < 50% of animal origin); to provide 10%-12% of total energy

Fat

22-28 g (including intrinsic fat in foods); to provide 20% - 25% of total energy
Saturated fat: < 7-9 g (up to 1/3 of total fat); mono-unsaturated: 7-9 g;
polyunsaturated: 7-9 g (Ratio of saturated to unsaturated: < 1 Amount of mono-unsaturated fat may be greater, provided ratio of saturated to unsaturated is observed and limit on total fat calories is not exceeded)
Cholesterol not to exceed 100 mg

Fibre

< 8 g or < 10 g, depending on whether determined as water-soluble or as crude fibre

Vitamins

Vitamin A: 300 RE (1 RE [retinol equivalent] = 1 µg of retinol or 6 µg of beta-carotene)
Vitamin C: 20 mg; preferably ingested with meals to improve absorption of iron
Folates: Folates: 80 µg. A supplement of 200-300 µg per day is often needed during pregnancy
Thiamine: 0.4 mg
Riboflavin: 0.6 mg
Niacin: 7 mg (or equivalent: 60 mg of tryptophan = 1 mg of niacin)

Minerals

Iron: 5, 7, or 14 mg for diets with high, intermediate, or low bioavailability of iron respectively. A supplement of 30-60 mg per day is often needed during pregnancy
Zinc: 6-10 mg; need varies depending on the source and on other components in the diet (e.g. animal sources, phytates, etc.)
Calcium: 500 mg. More foods rich in calcium should be given to preschool children and adolescents, and during pregnancy and lactation
Iodine: 100-200 µg per day in areas without goitre; 300-400 µg per day in areas with goitre (fortification of salt usually necessary)
Fluorine: 0.7-1.0 mg; sources of water with I ppm or more will meet this need
Sodium: Limit total ingestion of salt to 10 µg per day (preferably less)

Values are per 1,000 kcal of dietary energy except as otherwise indicated.

TABLE 8. Considerations in guideline development

A wide variety of foods is the best assurance of a good diet
Promote beneficial interactions (e.g. vitamin C and iron)
Minimize undesirable interactions (e.g. tea and iron)
Some animal protein is highly desirable, but not essential
Some milk is desirable, but not essential (use low-fat if necessary)
Cholesterol limit does not require total elimination of eggs
Diet must have adequate energy and nutrient density (especially for young children and the elderly)
Reduce salt intake (the lower, the better)
Maintain physical activity for cardiovascular fitness
Maintain appropriate weight
Limit use of alcohol
Avoid tobacco in any form

The needs for additional nutrients during adolescence, pregnancy, and lactation should be met by giving these persons a larger amount of food or larger portions of the foods rich in particular nutrients. Only in special situations, such as women who are beginning their pregnancies with low reserves of body iron or who have diets poor in folates, should the administration of special foods or supplementation with pharmacological preparations be considered. There still are not sufficient data to justify specific nutritional goals for old people.

If foods are eaten in sufficient quantities to satisfy energy needs, the needs for the nutrients mentioned in table 7 will also be fulfilled-with the exception, for many populations, of iodine and fluorine. At the same time, foods that supply those nutrients in the quantities described usually will provide adequate amounts of other essential vitamins and minerals that are not included in the table.

In the case of iodine, dietary deficiency of this mineral can be prevented by the use of iodized salt. In the case of fluorine, a deficiency can be corrected by the fluoridation of water or salt, or by using fluoridated dentifrices and topical applications of fluorine.

In populations in which iron-deficiency anaemia is prevalent, the diet does not provide highly bioavailable forms of this mineral and parasitosis and infections that produce blood loss are frequent, the fortification of sugar, salt, or some other staple food should be considered until the diet and hygienic conditions of the population can be improved.

A similar argument could be made concerning retinol in populations in which hypovitaminosis A is prevalent and the diet is deficient in vitamin A and carotenes.

In any case, the figures given in table 7 will need to be revised when changes in nutritional and metabolical knowledge or modifications of nutritional pathology in the countries of Latin America demand it.

References

1. Bengoa JM, Torún B, Behar M, Scrimshaw NS. Guias de alimentación: bases pare su desarrollo en America Latina. Caracas, Venezuela: Fundación Cavendes, 1988

2. Energy and protein requirements. Report of a joint FAO/WHO/UNU expert consultation. WHO technical report series, no. 724. Geneva: WHO, 1985.

3. Passmore R, Nicol BM, Rao MN. Handbook on human nutritional requirements. FAO nutritional studies, no. 28. WHO monograph series, no. 61. Rome: FAO, 1974.

4. Rose WC. The amino acid requirements of adult men. Nutr Abstr Rev 1957;27:631-47.

5. Young VR. Kinetics of human amino acid metabolism: nutritional implications and some lessons. McCollum award lecture. Am J Clin Nutr 1987;46:709-25.

6. Young VR, Bier DM. A kinetic approach to the determination of amino acid requirements. Nutr Rev 1987.

7. Kolonel LN, Hankin JH, Law J, Xhua AY, Nomue MY, Hinsa M. Nutrient intakes in relation to cancer incidence, Hawaii. Br J Cancer 1981;44:3232-339.

8. Hornstra G. Dietary lipids and cardiovascular disease: effect of palm oil. Proceedings of the International Oil Palm/Palm Oil Conferences, Kuala Lumpur, Malaysia, June-July 1987.

9. Layrisse M. Requerimientos de nutrientes que participan en la eritropoyesis. Arch Lat Nutr 1989;38(2) (in press).

10. Nordin BEC. Calcium. J Food Nutr 1986;42:67-82.

11. Food and Nutrition Board, National Research Council. Toward healthful diets. Washington, DC: National Academy of Sciences, 1980.

12. Department of National Health and Welfare. Canada's food guide handbook. Rev. ed. Ottawa: Supply and Services, 1982.

13. Food and Nutrition Board. Recommended dietary allowances. 6th rev. ed. National Research Council publication 1164. Washington, DC: National Academy of Sciences, 1964.

Contents - Previous - Next