Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- Most of the iron in the body is found in hemoglobin in red blood cells where it helps to carry oxygen and deliver it to tissues throughout the body.
- Iron is also involved in various enzyme systems (e.g., cytochromes involved in energy metabolism).
- In the most severe cases of iron deficiency, the deficiency causes anemia (low hemoglobin concentrations). Iron deficiency without anemia can also occur and produce health consequences.
Prevalence of Deficiency:
- Iron deficiency is the most common nutrient deficiency in the world. The World Health Organization has estimated that 2 billion people worldwide (40% of the world’s population) have anemia and 50% (1 billion) of these cases are due to iron deficiency.
- The majority of cases of anemia are in people living in developing countries where it is estimated that 50% are anemic. In some regions, such as in the Indian subcontinent and in sub-Saharan Africa, the prevalence of anemia is much higher (e.g., up to 90% of pregnant women).
- It is estimated that another 1 billion people worldwide have iron deficiency without anemia.
- The highest prevalence of iron deficiency is in infants, children, adolescents, and women of child-bearing age.
Risk Factors for Deficiency:
- The most common cause of iron deficiency is an inadequate iron supply in the diet to meet the body’s demands for iron.
- Dietary risk factors leading to an inadequate iron supply:
- Low intake of flesh foods (meat, poultry, fish) which provide heme iron
- High intakes of cereals and legume which cause poor absorption of iron (due to phytates)
- Low intakes of vitamin C from fruits and vegetables
- Developing countries and/or communities consuming vegetarian diets:
- The bioavailability of iron is often low in vegetarian diets (or in developing countries where meat intake is low) because meat is the best source of iron, and inhibitors of iron absorption (e.g., phytates, polyphenols) are usually high in these diets.
- Increased iron demands or iron losses:
- Iron requirements are especially high during periods of growth (e.g., during infancy and toddlerhood)
- Intestinal blood loss due to infestation with hookworm or the parasite schistosomiasis ascaris increases the risk for deficiency.
- Infants and children are at particular risk for iron deficiency.
- Infants born premature and/or low birth weight:
- Infant iron stores that accumulate during the third trimester and early postnatal life, along with the iron supplied in human milk, are adequate to meet the iron needs of infants during the first 4 to 6 months of life. This accumulation of iron during the third trimester and first couple months of life is disrupted in infants born preterm and/or low birth weight. These infants may need an extra supply of iron during the first six months.
- Infants and toddlers 6 to 24 months of age:
- Iron requirements increase after 4 to 6 months of age. During the weaning period, the dietary iron requirements in relation to the energy requirements are considerably high. The fast growth rates during this time, which increase the iron demands, in combination with limited iron stores increase the risk for deficiency if enough iron is not supplied in the diet.
- Anemia is diagnosed when hemoglobin concentrations are low. Iron deficiency is not the only cause of anemia, and therefore, iron deficiency anemia must be diagnosed by a low hemoglobin in combination with iron deficiency.
- Iron deficiency without anemia is diagnosed when there are several positive indicators of iron deficiency, but hemoglobin concentrations are normal
- Indicators of iron deficiency:
- Indicators include: Low hemoglobin, low serum ferritin (iron stores), low transferrin receptors in serum, low serum transferrin saturation, elevated erythrocyte protoporphyrin.
- There are limitations for each biochemical indicator of iron status. For instance, most indicators are affected by the presence of infection. Therefore, a combination of indicators is recommended to diagnose iron deficiency.
Dietary Sources and Bioavailability:
- There are 2 sources of dietary iron: heme iron and non-heme iron.
- Heme iron:
- Heme iron is best source of iron because it is easily absorbed.
- Sources: Meat, poultry, and fish (heme iron is found in the hemoglobin and myoglobin of flesh foods).
- Inhibitors of absorption: Calcium is the only dietary component to inhibit the absorption of heme iron.
- Non-heme iron:
- Sources: cereals, pulses, legumes, fruits, and vegetables
- Enhancers of absorption:
- Ascorbic acid (vitamin C): Ascorbic acid is the strongest promoter of non-heme iron and may offset many of the negative effects of iron inhibitors if it is provided in sufficient amounts.
- Meat increases the absorption of non-heme iron.
- Fermented foods (vegetables such as sauerkraut, fermented soy sauces) also improve non-heme iron absorption.
- Inhibitors of absorption:
- Phytates are chemicals found in cereals and grains. Phytates bind iron making it unavailable for absorption. Examples include bran, whole-wheat flours (white-wheat flour contains less phytate), and oats. Even small amounts of phytates can have a negative effect on absorption.
- Fermentation (i.e., using yeast in dough for making bread) can reduce the inhibiting effects of phytates. Using germinated grains also decreases the effects of phytates.
- Ascorbic acid, if in sufficient amounts, can counteract the negative effects of phytates.
- Iron-binding phenolic compounds, found in tea, coffee, cocoa, some vegetables (especially green leafy vegetables), some herbs (e.g., oregano), and betel leaves (common in parts of Asia), interfere with absorption.
- Calcium interferes with iron absorption. Because calcium is also an essential nutrient, a practical solution is to consume iron and calcium at different meals.
- Soy may interfere with non-heme iron absorption. Soy foods inhibit iron absorption. However, soy foods also contain iron, so the negative effects are often offset. Furthermore, the addition of sufficient ascorbic acid can offset the negative effects of soy, especially in infant foods containing soy. Fermented soy products may improve iron absorption.
Recommended Nutrient Intakes (mg/day): The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization. The RNI depends on the bioavailability of iron (i.e., the enhancers and inhibitors of iron absorption that are present in the diet).
High Bioavailability: Developed Countries (12-15%)
Low Bioavailability: Developing Countries (5 – 10 %)
6.2 – 7.7
9.3 – 18.6
3.9 – 4.8
5.8 – 11.6
- There has been concern that high iron intakes associated with pharmaceutical iron supplementation may increase the incidence of infections in children and increase the risk for cardiovascular disease and cancer in adults.
- Iron fortification of infant cereals and formulas does not appear to increase infection rates in children under 18 months of age.
- The tolerable upper limit (UL) for iron in children ages 1-3 years is 40 mg/day.
- Three strategies recommended for decreasing iron deficiency include:
- Iron supplementation (iron tablets) given to target groups
- Fortification of certain foods (e.g., flour):
- Fortified cereals have been effective in reducing the rates of iron deficiency in infants and children in developed children. Ascorbic acid (vitamin C) is usually added to fortified cereal-based complementary foods for infants and toddlers to increase absorption.
- Fortification of infant formulas with ascorbic acid has also been effective.
- Education, especially focused on increasing the bioavailability of iron in the diet.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Anemia (low hemoglobin)
- Reduced work capacity and endurance
- Impaired immunological defense against infections
- Impaired cognitive and behavioral development and impaired school performance
- Iron deficiency in infants and children, when the brain is undergoing significant development, has long-lasting effects on cognitive and behavioral development.
- Increased risk for childhood mortality (with severe anemia)
- May impair vitamin A metabolism and iodine metabolism.
Iron. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004:246-278.