Iron Deficiency : Part 4

by CDC

(Page 4 of 11)

Early introduction (i.e., before age 1 year) of whole cow's milk and consumption of greater than 24 oz of whole cow's milk daily after the 1st year of life are risk factors for iron deficiency because this milk has little iron, may replace foods with higher iron content, and may cause occult gastrointestinal bleeding. Because goat's milk and cow's milk have similar compositions, infants fed goat's milk are likely to have the same risk for developing iron deficiency as do infants fed cow's milk. Of all milks and formulas, breast milk has the highest percentage of bioavailable iron, and breast milk and iron-fortified formulas provide sufficient iron to meet an infant's needs. Iron-fortified formulas are readily available, do not cost much more than non-iron-fortified formulas, and have few proven side effects except for darker stools. Controlled trials and observational studies have indicated that iron-fortified formula causes no more gastrointestinal distress than does non-iron-fortified formula, and there is little medical indication for non-iron-fortified formula.

After age 24 months, when the growth rate of children slows and the diet becomes more diversified, the risk for iron deficiency drops. In children aged greater than 36 months, dietary iron and iron status are usually adequate. For these older children, risks for iron deficiency include limited access to food (e.g., because of low family income or because of migrant or refugee status), a low-iron or other specialized diet, and medical conditions that affect iron status (e.g., inflammatory or bleeding disorders).

During adolescence (ages 12- less than 18 years), iron requirements and hence the risk for iron deficiency increase because of rapid growth. Among boys, the risk subsides after the peak pubertal growth period. Among girls and women, however, menstruation increases the risk for iron deficiency throughout the childbearing years. An important risk factor for iron-deficiency anemia among nonpregnant women of childbearing age is heavy menstrual blood loss (greater than or equal to 80 mL/month), which affects an estimated 10% of these women in the United States. Other risk factors include use of an intrauterine device (which is associated with increased menstrual blood loss), high parity, previous diagnosis of iron-deficiency anemia, and low iron intake. Use of oral contraceptives is associated with decreased risk for iron deficiency.

Data from CSFII suggest that only one fourth of adolescent girls and women of childbearing age (12-49 years) meet the recommended dietary allowance for iron through diet. Indeed, data from the complete NHANES III indicated that 11% of nonpregnant women aged 16-49 years had iron deficiency and that 3%-5% also had iron-deficiency anemia.

Among pregnant women, expansion of blood volume by approximately 35% and growth of the fetus, placenta, and other maternal tissues increase the demand for iron threefold in the second and third trimesters to approximately 5.0 mg iron/day. Although menstruation ceases and iron absorption increases during pregnancy, most pregnant women who do not take iron supplements to meet increased iron requirements during pregnancy cannot maintain adequate iron stores, particularly during the second and third trimesters. After delivery, the iron in the fetus and placenta is lost to the woman, but some of the iron in the expanded blood volume may be returned to the woman's iron stores.

The prevalence of anemia in low-income, pregnant women enrolled in public health programs in the United States has remained fairly stable since 1979. In 1993, the prevalence of anemia among these women was 9%, 14%, and 37% in the first, second, and third trimesters, respectively. Comparable data for the U.S. population of all pregnant women are unavailable. The low dietary intake of iron among U.S. women of childbearing age, the high prevalence of iron deficiency and iron-deficiency anemia among these women, and the increased demand for iron during pregnancy suggest that anemia during pregnancy may extend beyond low-income women.

Published data on iron supplement use by a representative sample of pregnant U.S. women are limited. In the 1988 National Maternal and Infant Health Survey of a nationally representative sample of U.S. women who delivered a child in that year, 83% of respondents reported that they took supplements with multiple vitamins and minerals greater than or equal to 3 days/week for 3 months after they found out they were pregnant. Significantly smaller percentages of black women; Eskimo, Aleut, or American Indian women; women aged less than 20 years; and women having less than a high school education reported taking these supplements. In this survey, self-reported use of supplementation was within the range found in a review of studies using objective measures to estimate adherence (e.g., pill counts and serum ferritin concentration). The survey results suggest that the groups of women at high risk for iron deficiency during nonpregnancy are less likely to take supplements with multiple vitamins and minerals during pregnancy. This survey did not question respondents about changes in supplement use during pregnancy or what dose of iron supplements was consumed.

In the United States, the main reasons for lack of a recommended iron supplementation regimen during pregnancy may include lack of health-care provider and patient perceptions that iron supplements improve maternal and infant outcomes, complicated dose schedules, and uncomfortable side effects (e.g., constipation, nausea, and vomiting). Low-dose supplementation regimens that meet pregnancy requirements (i.e., 30 mg iron/day) and reduce unwanted side effects are as effective as higher dose regimens (i.e., 60 or 120 mg iron/day) in preventing iron-deficiency anemia. Simplified dose schedules (e.g., 1 dose/day) may also improve compliance. Methods to improve compliance among pregnant women at high risk for iron deficiency require further study.

Among men (males aged greater than or equal to 18 years) and postmenopausal women in the United States, iron-deficiency anemia is uncommon. Data from NHANES III indicated that less than or equal to 2% of men aged greater than or equal to 20 years and 2% of women aged greater than or equal to 50 years had iron-deficiency anemia. Data from CFSII indicate that most men and most women aged greater than or equal to 50 years meet the recommended dietary allowance for iron through diet. In a study of adults having iron-deficiency anemia, 62% had clinical evidence of gastrointestinal bleeding as a result of lesions (e.g., ulcers and tumors). In NHANES I, which was conducted during 1971-1975, about two thirds of anemia cases among men and postmenopausal women were attributable to chronic disease or inflammatory conditions. The findings of these studies suggest that, among these populations, the primary causes of anemia are chronic disease and inflammatory conditions and that low iron intake should not be assumed to be the cause of the anemia.

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