Abstract

Micronutrient fortification of foods is now a highly relevant tool worldwide for overcoming micronutrient deficiency. Recent data show that subclinical zinc deficiency is widespread; in Mexico a national survey showed that 25% of children less than age 11 y had plasma zinc concentrations below 10.0 μmol/L (65 μg/dL). Copper deficiency in populations is unknown but copper supplementation is recommended to accompany zinc supplementation. Of the foods available for fortification, staple cereals are very good candidates for reducing micronutrient deficiencies. Because of its higher stability and lower cost, we recommend fortification of cereal flours with zinc oxide, which is absorbed as well as the less stable and more expensive forms of zinc. Depending on the amount of the food that is expected to be eaten, zinc fortification of staple foods could be 20–50 mg/kg of flour. For copper fortification the safer compound is copper gluconate. Copper sulfate is significantly less expensive, but an evaluation of potential physicochemical reactions that affect the final food product is recommended. The suggested amount of copper added to staple foods is 1.2–3.0 mg/kg of flour. For food supplements designed as part of supplementation programs to reduce micronutrient deficiency in children less than age 3 y, a dose of the final product (usually ∼40–50 g) should contain ∼4–5 mg of zinc and ∼0.2–0.4 mg of copper depending on the habitual diet, magnitude of deficiencies and period of supplementation.

The magnitude of marginal zinc deficiency in developing countries is unknown, but the results of many studies, most of which have been conducted within the past few years, attest to widespread zinc deficiency in children in different regions of the world. The clinical signs of marginal zinc deficiency are depressed immunity, impaired taste and smell, onset of night blindness, impairment of memory and decreased spermatogenesis (1,2). Functional consequences of marginal zinc deficiency have also been documented in populations in developing countries. Zinc supplementation in children is associated with substantial reduction in the duration and severity of diarrhea and pneumonia in developing countries (3,4). Although supported by only a few studies, there are some suggestions that zinc supplementation might also improve the neuropsychologic performance of children with marginal zinc deficiency (5).

The incidence of zinc deficiency in Mexican children is high. Table 1 shows the percentage of children with serum zinc concentrations < 10.0 μmol/L (65 μg/dL). Children are divided by age and by rural and urban population (6); 25% of all children between ages 0 and 11 y were deficient. Rural areas had a higher incidence of zinc deficiency (40%) than did urban areas (18%).

TABLE 1

Zinc deficiency in children in rural and urban populations of Mexico

Age group Percent deficient1 
Rural Urban Total 
0–2 24.7 36.6 33.9 
3–4 55.8 21.6 32.9 
5–6 34.3 13.9 21.4 
7–8 28.3 15.2 19.3 
9–10 37.1 13.6 21.6 
11 41.1 16.7 24.4 
Total 40.0 18.2 25.3 
Age group Percent deficient1 
Rural Urban Total 
0–2 24.7 36.6 33.9 
3–4 55.8 21.6 32.9 
5–6 34.3 13.9 21.4 
7–8 28.3 15.2 19.3 
9–10 37.1 13.6 21.6 
11 41.1 16.7 24.4 
Total 40.0 18.2 25.3 
1

Serum zinc concentrations below 10.0 μmol/L (65 μg/dL).

TABLE 1

Zinc deficiency in children in rural and urban populations of Mexico

Age group Percent deficient1 
Rural Urban Total 
0–2 24.7 36.6 33.9 
3–4 55.8 21.6 32.9 
5–6 34.3 13.9 21.4 
7–8 28.3 15.2 19.3 
9–10 37.1 13.6 21.6 
11 41.1 16.7 24.4 
Total 40.0 18.2 25.3 
Age group Percent deficient1 
Rural Urban Total 
0–2 24.7 36.6 33.9 
3–4 55.8 21.6 32.9 
5–6 34.3 13.9 21.4 
7–8 28.3 15.2 19.3 
9–10 37.1 13.6 21.6 
11 41.1 16.7 24.4 
Total 40.0 18.2 25.3 
1

Serum zinc concentrations below 10.0 μmol/L (65 μg/dL).

The existence of mineral deficiency in Mexico is associated with the intake of diets based on plant foods. A large proportion of the population, especially in rural areas, habitually ingests a diet based on corn, which is eaten as tortillas with beans and variable amounts of vegetables and fruits. The intake of meat is highly variable ranging from no intake to three to four times per week depending on income. Previous studies demonstrated that zinc bioavailability in such diets is very low (7). This association with diet is the main reason for the much higher incidence of zinc deficiency in rural areas of Mexico.

The average per capita intake of corn in Mexico is ∼120 kg/y, which is the highest per capita intake in the world. The corn tortilla is the staple food eaten by most of the population in significant amounts, which makes it a good vehicle for micronutrient addition. Corn tortillas are prepared from corn flour. A formula recently developed for corn flour fortification contains zinc and other micronutrients (8).

Nutrient fortification of complementary foods

The addition of minerals to foods began in South America in 1833 when Boussinggault, a French chemist, recommended the addition of iodine to salt as a public measure to prevent goiter. The addition of iodine to salt has been one of the most successful uses of food fortification in several countries. The number of foods fortified with minerals and other nutrients is continuously increasing.

Food fortification is generally carried out to restore nutrients that are lost during harvesting, refinement, storage, cooking or processing of foods. This process is known as nutrient restoration of foods and is applied to many foods, such as cereals, for which many countries have regulatory laws. Food fortification may also be a strategy for increasing the intake of some nutrients that are known to be deficient in specific population groups, and thus fortification contributes to reducing the incidence of nutrient deficiencies, especially of vitamins and minerals. Recommendations in this paper are given for the addition of zinc and copper to food to reduce micronutrient deficiencies.

Evaluation of vehicles for nutrient addition

Zinc and copper can be added to many foods including milk, cereals, flours, fruit juices, sugar and water. When the objective of food fortification is to increase the intake of specific nutrients that are known to be deficient in a population, the selection of an adequate vehicle is crucial for program success. The following characteristics should be met when choosing a vehicle for such purposes (9): 1) Food chosen as a vehicle should be ingested by the target population in sufficient quantities and with a small variability in the amount ingested. 2) The fortified food should be stable and physicochemical properties such as appearance, texture and flavor should not change when the nutrient is added. 3) The added nutrient should be relatively bioavailable and well tolerated. 4) Fortification of the food should not significantly increase its price. 5) Fortification should be carried out with available ingredients and technology and preferably at low cost.

Zinc fortification of foods

Successful fortification of a food depends on the fortificant acting in a relatively benign manner in the food. Unfortunately, this level of chemical inertness is often associated with insolubility and relatively poor bioavailability. Minerals are chemically reactive substances, not the inert compounds they are often thought to be. This reactivity becomes particularly apparent in a food in the presence of moisture, when reactions may occur with free radicals, other food components and oxygen. Any of these reactions could result in undesirable changes in color, flavor and appearance or could affect nutrient stability. Potential changes in physicochemical and functional properties as well as changes in nutrient content during the required shelf life of fortified foods need to be evaluated before any firm recommendation in dose and source of minerals is made.

In the United States, minerals used for fortification of foods are classified by the Food and Drug Administration as generally recognized as safe (GRAS). GRAS classification may be based on scientific procedures that use the same quantity and quality of evidence required to obtain approval for a food additive or the substance may have demonstrated evidence through its use in food (11). There are currently five zinc compounds listed as GRAS that may be used in fortifying foods: zinc sulfate, zinc chloride, zinc gluconate, zinc oxide and zinc stearate (11). Of these compounds, zinc oxide is by far the most commonly used. Data compiled by the National Academy of Sciences on the amount of zinc compounds used by food manufacturers in the United States are shown in Table 2(12,13). Zinc oxide is the compound most commonly used and its consumption has increased significantly.

TABLE 2

Amounts of zinc compounds used by food manufacturers in the United States1

Zinc compound Amounts of zinc used 
1970 1975 1976 1982 1987 
 kg 
Zinc chloride ND ND ND 10 10 
Zinc gluconate 3024 ND 10,578 2529 9170 
Zinc oxide ND 5448 42,177 33,551 102,150 
Zinc stearate ND ND ND 218 ND 
Zinc sulfate 2806 12,485 2992 37,183 5818 
Zinc compound Amounts of zinc used 
1970 1975 1976 1982 1987 
 kg 
Zinc chloride ND ND ND 10 10 
Zinc gluconate 3024 ND 10,578 2529 9170 
Zinc oxide ND 5448 42,177 33,551 102,150 
Zinc stearate ND ND ND 218 ND 
Zinc sulfate 2806 12,485 2992 37,183 5818 
1

Data compiled by the U.S. National Academy of Sciences on the amount of zinc compounds used by food manufacturers in the United States (12, 13). ND, not determined.

TABLE 2

Amounts of zinc compounds used by food manufacturers in the United States1

Zinc compound Amounts of zinc used 
1970 1975 1976 1982 1987 
 kg 
Zinc chloride ND ND ND 10 10 
Zinc gluconate 3024 ND 10,578 2529 9170 
Zinc oxide ND 5448 42,177 33,551 102,150 
Zinc stearate ND ND ND 218 ND 
Zinc sulfate 2806 12,485 2992 37,183 5818 
Zinc compound Amounts of zinc used 
1970 1975 1976 1982 1987 
 kg 
Zinc chloride ND ND ND 10 10 
Zinc gluconate 3024 ND 10,578 2529 9170 
Zinc oxide ND 5448 42,177 33,551 102,150 
Zinc stearate ND ND ND 218 ND 
Zinc sulfate 2806 12,485 2992 37,183 5818 
1

Data compiled by the U.S. National Academy of Sciences on the amount of zinc compounds used by food manufacturers in the United States (12, 13). ND, not determined.

Bioavailability of added compounds

Because minerals are added to foods to increase nutritive value, the major factor to be considered in choosing the appropriate compound to be added to a particular food is bioavailability. However, using an exceedingly bioavailable compound does not make sense if the food is rendered unpalatable or unacceptable as a result of physicochemical changes. Minerals are chemically reactive compounds and their bioavailability will be greatly affected by interactions with food components when added or during processing and storage. Therefore, bioavailability of a mineral in food is not strictly a function of the bioavailability of the compound chosen.

To make judgments about bioavailability and functionality so that the most adequate compound may be chosen, it is important to understand the major physicochemical properties that affect bioavailability and how they may be influenced by food environment, processing and storage. These properties have been discussed by Clydesdale (10) and include solubility, charge density, reduction potential and pH, complex formation and the effect of processing.

Solubility.

Even though it is believed that minerals must be soluble in the intestine to be absorbed, not all soluble minerals are absorbed. Because solubility depends on the type and strength of the chemical bonds, all chemical reactions occurring in the food environment must be understood for mineral solubility and bioavailability to be understood.

Charge density.

Charge density is important to cell permeability because the rate at which a molecule diffuses across the lipid bilayer of the cell membrane depends on its size and degree of polarity. Small nonpolar molecules readily dissolve in the lipid bilayer and therefore diffuse across it.

Reduction potential and pH.

The transition metals including zinc and copper exist in solution as hydrates rather than ions. As pH is raised, the hydrates lose protons and form the less soluble or insoluble hydroxides. This means that acidic foods may be the logical choice for fortification with minerals.

Complex formation.

Solubility may be due to the inherent chemical nature of the mineral, its immediate environment and the presence of food components that will bond with the mineral to form a complex or chelate. Enhancers and inhibitors act as mineral-binding agents, and it is merely the nature of the bond that they form and the solubility of their complex that determine their role as either an enhancer or an inhibitor.

Effect of processing.

Processing of food may influence mineral bioavailability depending on its effect on any of the factors previously discussed.

Absorption of zinc compounds added to corn flour

Even though zinc oxide is the zinc compound that has been most widely used for zinc fortification of foods (Table 2), some authors have suggested that this compound should be avoided because of its lower solubility (14,15). As stated previously, solubility is only one important factor that affects bioavailability. The use of zinc oxide has some advantages over the use of other zinc compounds because it is more stable and does not significantly change the food to which it is added. Zinc oxide is also much less expensive than other zinc compounds (Table 3). Zinc sulfate is the second most used source of zinc and is more soluble than zinc oxide. Its stability depends on the food matrix to which it is added. To compare the absorption of zinc oxide with zinc sulfate, we conducted a study in 10 women using stable isotopes of zinc in corn tortilla (unpublished observations). A summary of the fractional absorption results are shown in Table 4; the fractional absorption of zinc oxide added to corn tortillas was similar to that of zinc sulfate.

TABLE 3

Relatively cost of commonly used zinc and copper sources

Nutrient source Cost Contained zinc Cost of nutrient 
 US$/kg US$/kg of nutrient 
Zinc    
    Zinc oxide 3.4 80.0 4.25 
    Zinc sulfate 4.15 32.0 12.96 
Copper    
    Copper gluconate 34.0 14.0 242 
    Copper sulfate 20.0 25.5 78 
Nutrient source Cost Contained zinc Cost of nutrient 
 US$/kg US$/kg of nutrient 
Zinc    
    Zinc oxide 3.4 80.0 4.25 
    Zinc sulfate 4.15 32.0 12.96 
Copper    
    Copper gluconate 34.0 14.0 242 
    Copper sulfate 20.0 25.5 78 
TABLE 3

Relatively cost of commonly used zinc and copper sources

Nutrient source Cost Contained zinc Cost of nutrient 
 US$/kg US$/kg of nutrient 
Zinc    
    Zinc oxide 3.4 80.0 4.25 
    Zinc sulfate 4.15 32.0 12.96 
Copper    
    Copper gluconate 34.0 14.0 242 
    Copper sulfate 20.0 25.5 78 
Nutrient source Cost Contained zinc Cost of nutrient 
 US$/kg US$/kg of nutrient 
Zinc    
    Zinc oxide 3.4 80.0 4.25 
    Zinc sulfate 4.15 32.0 12.96 
Copper    
    Copper gluconate 34.0 14.0 242 
    Copper sulfate 20.0 25.5 78 
TABLE 4

Fractional absorption of zinc oxide and zinc sulfate added to corn tortilla

Zinc source Fractional absorption 
Tortilla + zinc oxide 36.8 ± 16.9 
Tortilla + zinc sulfate 37.2 ± 22.7 
Tortilla alone 35.6 ± 23.8 
Zinc source Fractional absorption 
Tortilla + zinc oxide 36.8 ± 16.9 
Tortilla + zinc sulfate 37.2 ± 22.7 
Tortilla alone 35.6 ± 23.8 
TABLE 4

Fractional absorption of zinc oxide and zinc sulfate added to corn tortilla

Zinc source Fractional absorption 
Tortilla + zinc oxide 36.8 ± 16.9 
Tortilla + zinc sulfate 37.2 ± 22.7 
Tortilla alone 35.6 ± 23.8 
Zinc source Fractional absorption 
Tortilla + zinc oxide 36.8 ± 16.9 
Tortilla + zinc sulfate 37.2 ± 22.7 
Tortilla alone 35.6 ± 23.8 

Mineral interactions: zinc, copper and iron

Minerals with similar physical and chemical properties and electronic structure will act antagonistically to each other in biological systems (16). There is some concern that the addition of zinc to foods could increase zinc intake to a level that could affect copper absorption (17). High intakes of zinc can induce synthesis of the copper-binding metallothionein in the mucosal cell; this protein sequesters copper, making it unavailable for transfer, and thus decreases copper absorption (18). Although a negative effect of typical zinc intakes on copper absorption has not been demonstrated, the possibility of adding conservative amounts of copper to zinc-fortified foods should be considered.

Another concern is that many zinc-fortified foods also contain added iron. Whittaker (11) reviewed studies testing the effect of iron on zinc absorption and found that in many studies iron decreased zinc absorption when added to water, but only one study showed a negative effect of iron on zinc absorption when added to foods. Sandstrom et al. (19) showed a negative effect when iron was added in a 25:1 ratio with zinc. Corn flour in Mexico is being fortified with zinc (20 mg/kg) and iron (30 mg/kg). To evaluate the potential negative effect of iron on zinc absorption, we carried out a study using stables isotopes of zinc (unpublished observations). Fractional absorption of zinc in 10 women consuming tortillas fortified with zinc to which different amounts of iron were added showed no effect of iron fortification (Table 5).

TABLE 5

Fractional absorption of zinc sulfate in the presence of different amounts of iron added to corn tortilla

Zinc source1 Fractional absorption 
Tortilla + ZnSO4 33.84 ± 8.04 
Tortilla + ZnSO4 + 1× Fe 32.3 ± 15.5 
Tortilla + ZnSO4 + 2× Fe 32.8 ± 12.6 
Zinc source1 Fractional absorption 
Tortilla + ZnSO4 33.84 ± 8.04 
Tortilla + ZnSO4 + 1× Fe 32.3 ± 15.5 
Tortilla + ZnSO4 + 2× Fe 32.8 ± 12.6 
1

1× corresponds to 30 mg iron/kg of corn flour; 2× corresponds to 60 mg iron/kg of corn flour.

TABLE 5

Fractional absorption of zinc sulfate in the presence of different amounts of iron added to corn tortilla

Zinc source1 Fractional absorption 
Tortilla + ZnSO4 33.84 ± 8.04 
Tortilla + ZnSO4 + 1× Fe 32.3 ± 15.5 
Tortilla + ZnSO4 + 2× Fe 32.8 ± 12.6 
Zinc source1 Fractional absorption 
Tortilla + ZnSO4 33.84 ± 8.04 
Tortilla + ZnSO4 + 1× Fe 32.3 ± 15.5 
Tortilla + ZnSO4 + 2× Fe 32.8 ± 12.6 
1

1× corresponds to 30 mg iron/kg of corn flour; 2× corresponds to 60 mg iron/kg of corn flour.

Copper fortification of foods

The amount of copper added to foods is less than the amount of other minerals such as iron or zinc. The two main compounds that have been suggested for food fortification are copper gluconate and copper sulfate (Table 3). Copper sulfate is highly reactive and hygroscopic, and less expensive than copper gluconate. No studies have compared the absorption of these compounds or any other copper compound. With the information available, the use of copper gluconate is favored because of its stability. However, studies with the specific food to which copper is to be added will be required. The wide difference in cost largely justifies such a comparison.

Amount of nutrient considered for fortification

Amounts of fortificant to be added should be carefully evaluated, especially for minerals that may be hazardous to humans at some level of intake. The decision should be based on knowledge of the total amount of the fortified food that could be eaten and the amounts of the mineral in other foods that are eaten. The intake of some foods is highly variable in a population; this is the case for tortillas in Mexico. When variability of intake is high, it is preferable to be conservative in the amounts of mineral that are added to foods to avoid the risk of excessive intakes in a proportion of the population that regularly eats the fortified food in higher amounts. Table 6 shows recommended intakes and Tolerable Upper Intake Levels for zinc and copper suggested by the Dietary Reference Intakes of the U.S. National Academy of Sciences (20). Other countries where the intake of zinc and iron is associated with foods and diets with lower bioavailability may have their own recommendations for intake of these nutrients. These values could be used to help decide how much copper and zinc should be added to a specific food, an amount that will ultimately depend on the food vehicle and the purpose of food fortification.

TABLE 6

Recommended intakes and tolerable upper intake levels of zinc and copper in the United States1

Age group Zinc Copper 
Estimated average requirements Tolerable upper intake levels Estimated average requirements Tolerable upper intake levels 
 mg/d μg/d 
Infants     
    0–6 mo 200 ND 
    7–12 mo 220 ND 
Children     
    1–3 y 340 1,000 
    4–8 y 12 440 3,000 
Males     
    9–13 y 23 700 5,000 
    14–18 y 11 34 890 8,000 
    19–70 y 11 40 900 10,000 
    >70 y 11 40 900 10,000 
Females     
    9–13 y 23 700 5,000 
    14–18 y 34 890 8,000 
    19–70 y 40 900 10,000 
    >70 y 40 900 10,000 
Pregnancy     
    ≤18 y 12 34 1,000 8,000 
    19–50 y 11 40 1,000 10,000 
Lactation     
    ≤18 y 13 34 1,300 8,000 
    19–30 y 12 40 1,300 10,000 
Age group Zinc Copper 
Estimated average requirements Tolerable upper intake levels Estimated average requirements Tolerable upper intake levels 
 mg/d μg/d 
Infants     
    0–6 mo 200 ND 
    7–12 mo 220 ND 
Children     
    1–3 y 340 1,000 
    4–8 y 12 440 3,000 
Males     
    9–13 y 23 700 5,000 
    14–18 y 11 34 890 8,000 
    19–70 y 11 40 900 10,000 
    >70 y 11 40 900 10,000 
Females     
    9–13 y 23 700 5,000 
    14–18 y 34 890 8,000 
    19–70 y 40 900 10,000 
    >70 y 40 900 10,000 
Pregnancy     
    ≤18 y 12 34 1,000 8,000 
    19–50 y 11 40 1,000 10,000 
Lactation     
    ≤18 y 13 34 1,300 8,000 
    19–30 y 12 40 1,300 10,000 
1

Data from reference 20. ND, not determined.

TABLE 6

Recommended intakes and tolerable upper intake levels of zinc and copper in the United States1

Age group Zinc Copper 
Estimated average requirements Tolerable upper intake levels Estimated average requirements Tolerable upper intake levels 
 mg/d μg/d 
Infants     
    0–6 mo 200 ND 
    7–12 mo 220 ND 
Children     
    1–3 y 340 1,000 
    4–8 y 12 440 3,000 
Males     
    9–13 y 23 700 5,000 
    14–18 y 11 34 890 8,000 
    19–70 y 11 40 900 10,000 
    >70 y 11 40 900 10,000 
Females     
    9–13 y 23 700 5,000 
    14–18 y 34 890 8,000 
    19–70 y 40 900 10,000 
    >70 y 40 900 10,000 
Pregnancy     
    ≤18 y 12 34 1,000 8,000 
    19–50 y 11 40 1,000 10,000 
Lactation     
    ≤18 y 13 34 1,300 8,000 
    19–30 y 12 40 1,300 10,000 
Age group Zinc Copper 
Estimated average requirements Tolerable upper intake levels Estimated average requirements Tolerable upper intake levels 
 mg/d μg/d 
Infants     
    0–6 mo 200 ND 
    7–12 mo 220 ND 
Children     
    1–3 y 340 1,000 
    4–8 y 12 440 3,000 
Males     
    9–13 y 23 700 5,000 
    14–18 y 11 34 890 8,000 
    19–70 y 11 40 900 10,000 
    >70 y 11 40 900 10,000 
Females     
    9–13 y 23 700 5,000 
    14–18 y 34 890 8,000 
    19–70 y 40 900 10,000 
    >70 y 40 900 10,000 
Pregnancy     
    ≤18 y 12 34 1,000 8,000 
    19–50 y 11 40 1,000 10,000 
Lactation     
    ≤18 y 13 34 1,300 8,000 
    19–30 y 12 40 1,300 10,000 
1

Data from reference 20. ND, not determined.

Recommended zinc intakes shown in Table 6 for children aged 7 mo to 3 y were derived using a relatively high fractional absorption (0.3) of zinc from mixed foods. These recommended intakes could be different if zinc and copper are derived from plant foods with a lower bioavailability of the mineral, as is the case in most developing countries. The recommended daily intakes for zinc and copper in Mexico are shown in Table 7.

TABLE 7

Recommended daily intakes of zinc and copper in Mexico

Age group Zinc Copper 
 mg/d μg/d 
Infants   
    0–6 mo 200 
    7–12 mo 220 
Children   
    1–3 y 340 
    4–8 y 440 
Males   
    9–13 y 12 700 
    14–18 y 14 890 
    19–70 y 15 900 
    >70 y 15 900 
Females   
    9–13 y 12 700 
    14–18 y 12 890 
    19–70 y 12 900 
    >70 y 12 900 
Pregnancy 14 1000 
Lactation 16 1300 
Age group Zinc Copper 
 mg/d μg/d 
Infants   
    0–6 mo 200 
    7–12 mo 220 
Children   
    1–3 y 340 
    4–8 y 440 
Males   
    9–13 y 12 700 
    14–18 y 14 890 
    19–70 y 15 900 
    >70 y 15 900 
Females   
    9–13 y 12 700 
    14–18 y 12 890 
    19–70 y 12 900 
    >70 y 12 900 
Pregnancy 14 1000 
Lactation 16 1300 
TABLE 7

Recommended daily intakes of zinc and copper in Mexico

Age group Zinc Copper 
 mg/d μg/d 
Infants   
    0–6 mo 200 
    7–12 mo 220 
Children   
    1–3 y 340 
    4–8 y 440 
Males   
    9–13 y 12 700 
    14–18 y 14 890 
    19–70 y 15 900 
    >70 y 15 900 
Females   
    9–13 y 12 700 
    14–18 y 12 890 
    19–70 y 12 900 
    >70 y 12 900 
Pregnancy 14 1000 
Lactation 16 1300 
Age group Zinc Copper 
 mg/d μg/d 
Infants   
    0–6 mo 200 
    7–12 mo 220 
Children   
    1–3 y 340 
    4–8 y 440 
Males   
    9–13 y 12 700 
    14–18 y 14 890 
    19–70 y 15 900 
    >70 y 15 900 
Females   
    9–13 y 12 700 
    14–18 y 12 890 
    19–70 y 12 900 
    >70 y 12 900 
Pregnancy 14 1000 
Lactation 16 1300 

The fractional absorptions used for calculating zinc recommendations differ. For adults fractional absorptions of 0.41 and 0.48 were used to calculate Estimated Average Requirements of zinc for men and women, respectively, in the Dietary Reference Intakes for the United States (20). Fractional absorption of zinc from corn tortillas in Mexican women was found to range from 0.32 to 0.37. Because this is a staple food in Mexico, fractional absorptions of 0.35 and 0.30 were used to set the Mexican Recommended Daily Intakes (RDI) for adult women and men, respectively (Table 7) (21). RDI for zinc for children are also higher because of a lower fractional absorption considered in the calculations. If the U.S. Dietary Reference Intakes are to be used as the guide for selecting the amount of zinc and copper to be added to foods intended for children in developing countries, the Mexican RDI, which use a lower fractional absorption, could be a better estimate.

Conclusions and recommendations

Because of its higher stability and lower cost, we recommend fortification of cereal flours with zinc oxide, which has been demonstrated to have the same absorption as the less stable and more expensive forms of zinc. Depending on the amount of the food that is expected to be eaten, zinc fortification of staple foods could be done in an amount equivalent to 20–50 mg/kg of flour. For copper fortification, copper gluconate is the safer compound. Because it is significantly less expensive, copper sulfate could be used, but an evaluation of potential physicochemical reactions that affect the final food product is recommended. The amount of copper suggested for staple foods is 1.2–3.0 mg/kg of flour. For food supplements designed as part of supplementation programs to reduce micronutrient deficiencies in small children, one dose of the final product (usually ∼50 g), should contain 4–5 mg of zinc and 0.2–0.4 mg of copper depending on the habitual diet, magnitude of deficiencies and period of supplementation.

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Footnotes

1
Presented as part of the technical consultation “Nutrient Composition for Fortified Complementary Foods” held at the Pan American Health Organization, Washington, D.C., October 4–5, 2001. This conference was sponsored by the Pan American Health Organization and the World Health Organization. Guest editors for the supplement publication were Chessa K. Lutter, Pan American Health Organization, Washington, D.C.; Kathryn G. Dewey, University of California, Davis; and Jorge L. Rosado, School of Natural Sciences, University of Queretaro, Mexico.