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* Maternal and Child Nutrition Branch,
Chronic Disease Nutrition Branch, Division of Nutrition and Physical Activity, Centers for Disease Control and Prevention, Atlanta, GA 30341 and
** Department of International Health, Rollins School of Public Health, Emory University, Atlanta, GA, 30322
3To whom correspondence should be addressed. E-mail: mec0{at}cdc.gov.
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONLITERATURE CITED |
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17 mg/d among nonpregnant women, 58 mg/d among pregnant women and 57 mg/d among lactating women. Use of supplements that contain iron was associated with a significantly reduced prevalence of iron deficiency among women 19–50 y but not among other groups. Groups at highest risk of iron deficiency (e.g., low income and minority women) are often least likely to consume supplements containing iron, suggesting that supplement use is unrelated to actual need.
KEY WORDS: • iron supplements • iron deficiency • adolescents • childbearing age • women
The use of iron supplements is accepted as a treatment for nonhereditary anemia. The use of iron supplements for prophylaxis, however, is more controversial. Universal iron supplement use is recommended during pregnancy by the Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists to prevent anemia (1,2). Some conclude, however, that the current evidence for use of prophylactic iron during pregnancy to raise birth weight or lower the rate of preterm birth is insufficient (3,4). A recent critical review of the scientific evidence indicated that the biological effect of iron deficiency anemia on work capacity is sufficiently strong to justify improving iron status among adult women (5). These findings and current recommendations for the prevention of anemia support the prophylactic use of iron supplements for women at high risk of iron deficiency.
National goals call for a reduction in iron deficiency among women of reproductive age as well as a reduction in anemia among pregnant women and in women with disparities arising from ethnicity and income (6). Whereas women aged 50 y and older are at lower risk of iron deficiency, in 1999–2000, 12% of U.S. women aged 12–49 y were iron deficient (7). Minority women were at higher risk (7). Compared with 10% of nonHispanic white women, 22% of Mexican-American women and 19% of nonHispanic black women were iron deficient in 1999–2000 (7). The prevalence of iron deficiency among nonpregnant women aged 20–44 y increased 150% from 1976–1980 to 1988–1994 (8) and did not decline in 1999–2000 (7). The prevalence of anemia among low income pregnant women has remained the same at 30% since the 1980s (9). In addition, the prevalence of iron deficiency is 4.5 times higher among low income postpartum women than in women who never were pregnant, but the prevalence of iron deficiency remains similar for postpartum women who are not low income compared with women who never were pregnant (10).
One reason for a lack of reduction in iron deficiency may be inadequate iron intake during the childbearing years. Average dietary iron intake for women 20–49 y was 11 mg/d in 1977–78 and 13 mg/d in 1994–1996 (11). The average dietary intake is well above the estimated average requirement for iron of 8.1 mg/d for women in this age group (12), but the amount of iron absorbed from the diet may have decreased. From 1977–1978 to 1994–1996, the average daily consumption of grains, a source of the less absorbable nonheme iron, increased by 44%; meat, poultry and fish remained the same; but beef, a source of heme iron, decreased by >50% (11).
Data on iron intake from the diet are limited for pregnant and lactating women. Data from the third National Health and Nutrition Examination Survey, 1988–1994 (NHANES III), suggest that the median iron intake among pregnant women was 15 mg/d, below the estimated average requirement of 22 mg/d for this group (12). This suggests the majority of women in the United States consume inadequate amounts of iron from their diet during pregnancy. The median iron intake for lactating women was 21 mg/d, well above the estimated average requirement of 6.5–7 mg/d (12), suggesting that although low income postpartum women have a higher prevalence of iron deficiency than do non–low income women, the majority of lactating women consume an amount of dietary iron presently judged to be adequate.
Data on iron intake from supplements are also limited. In 1988 26% of U.S. mothers reported taking multivitamin-mineral supplements 3 or more times per week for at least 3 mo before pregnancy; 67% of black mothers and 84% of white mothers reported taking supplements 3 or more times per week for at least 3 mo during pregnancy (13). The average amount of iron from supplements in this survey is not known nor is the consumption of supplements by lactating women or older women.
To better understand the patterns of iron intake from supplements among U.S. adolescent girls and women and their relationship to iron deficiency, we determined the proportion of U.S. girls and women who consumed supplements containing iron in 1988–1994 by age, income, race/ethnic group and reproductive status. We also determined the amount of iron consumed from supplements and the association between supplement use and iron deficiency.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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Our study sample was restricted to females 14 y of age and older (n = 10,323). No female who reported currently being pregnant or breastfeeding a baby was <14 y of age. Women were excluded if they were missing information on supplement use (n = 1) or reproductive status (n = 276). The final sample included 10,046 adolescent girls and women.
The values for daily intake of iron supplements were calculated from a series of questions about the vitamins or minerals the subject had taken within the past month. Women and adolescents were asked whether they had taken any vitamins or minerals in the past month including those prescribed by a doctor and those not prescribed. Participants who answered affirmatively were asked to show the supplement containers and queried about the doses and duration of use.
We defined iron supplement use as consumption of supplements that contained iron. We also estimated the average daily intake of iron from supplements that contained iron. For example, if total supplemental iron for 1 mo was estimated to be 4800 mg, the average daily intake was calculated as 160 mg.
Reproductive status was based on self-reported data from the medical examination. Women who reported that they were currently pregnant were considered pregnant. Pregnancy testing was also conducted for women 17 y and older. We did not use this variable because we expected that women who knew they were pregnant may be more likely to take iron supplements than those who did not know they were pregnant. Of women who reported they were pregnant, three were also lactating. For the purpose of this analysis, these women were counted as pregnant and excluded from the subanalysis of lactating women. Trimester was based on the number of months pregnant as reported by the participant. First trimester was defined as 0–3-mo pregnant, second trimester as 4–6-mo pregnant and third trimester as 7-mo or more pregnant. Three women did not know how long they had been pregnant.
Ethnicity was based on self-reported data. Women who were of ethnicity other than Mexican-American, nonHispanic black or nonHispanic white (n = 450) were excluded from subanalysis of supplement use by race/ethnic group because of the small sample size and heterogeneity of this group.
The poverty income ratio is the total household income divided by the poverty threshold for the year of the interview (15). The poverty threshold is determined annually by the U.S. Bureau of the Census, taking into account geographic location, rate of inflation and family size (16). Women without information on household income or family size (n = 992) were excluded from analysis that included the poverty income ratio.
Self-reported iron treatment was determined by an affirmative response to the question, "Are you now or in the past 3 mo have you been on treatment for anemia sometimes called ‘tired blood’ or ‘low blood’ (include diet, iron pills, iron shots, or transfusions as treatment)?" Women without information on iron treatment (n = 299) were excluded from the analysis that examined the proportion of people taking supplements who were on treatment.
All iron assays were conducted at the NHANES laboratory, National Center of Environmental Health, Centers for Disease Control and Prevention. The methods for each of the iron assays have been reported (17). Iron deficiency was defined by at least two of three abnormal values for serum ferritin (<12 µg/L), transferrin saturation (<14% for ages 14–15 y or <15% for ages 16 y and over) or erythrocyte protoporphyrin (
1.24 µmol/L erythrocytes) (18,19). Analysis of the prevalence of iron deficiency by use of supplements containing iron excluded women who reported being on treatment for anemia or who were missing information on one or more of the iron indexes (n = 593).
We weighted all statistical analyses and used SUDAAN (version 7.5; Research Triangle Institute, Research Triangle Park, NC) to account for the complex sample design. All point estimates are crude rates. We set statistical significance at P < 0.05 for the comparisons of supplement use between groups.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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Among pregnant women, the intake of supplements that contained iron differed by trimester of pregnancy; of women in their first trimester 37 ± 9% (mean ± SE) consumed supplements that contained iron compared with 81 ± 5% and 82 ± 8% of women in their second and third trimesters, respectively (P = 0.018).
The distribution of iron intake was skewed (Table 2). Among women consuming supplements, the median intake of iron was 11 mg/d among nonpregnant, nonlactating adolescents; 17.5 mg/d among nonpregnant women; 58 mg/d among pregnant women; and 57 mg/d among nonpregnant, lactating women. The variation in the amount of iron consumed from supplements was largest among pregnant and lactating women.
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0.05), likely because of low numbers (analyses not shown). Among women taking supplements containing iron, a minority (11.0 ± 3.8% of pregnant and 11.8 ± 6.5% of nonpregnant, lactating women) reported being treated for anemia in the past 3 mo. The proportion among nonpregnant, nonlactating adolescents was 7.7 ± 4.1%; among women 19–50 y, 9.0 ± 1.4%; and among women 51 y and older, 6.2 ± 1.1%. The prevalence of iron deficiency was generally lower among nonpregnant adolescents and women who took supplements that contained iron than among those who did not (Table 3). This association was statistically significant among nonpregnant, nonlactating women aged 19–50 y but not other groups. The number of lactating women and of adolescents who took supplements was small. Among women 51 y of age and older, the prevalence of iron deficiency was very similar regardless of supplement status. Among pregnant women, trimester of pregnancy confounded the association between supplement use and iron deficiency because women in the first trimester were less likely to take supplements and be iron deficient than women in the later trimesters. Stratifying the pregnant women by trimester reduced the sample size further, hence we did not report these results.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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Minority and low income women of childbearing age who are at higher risk of iron deficiency (6,7) were, in general, less likely to take supplements than nonHispanic white women. Similar to the previous U.S. study (13), we found that nonHispanic black women were less likely to consume supplements than nonHispanic white women. Additionally, we found that Mexican-American women in most reproductive groups were less likely to take supplements that contain iron than were non-Hispanic white women and that low income women were in general less likely to consume supplements that contain iron.
We also found that pregnant women, and lactating women who consumed supplements that contain iron were taking larger doses of iron (58 and 57 mg/d, respectively) than the Tolerable Upper Intake Level (45 mg/d) (12). The median doses were similar to the amount of iron found in multivitamin-mineral and prenatal supplements during that time period. Additionally, fewer than 15% of the women who took supplements that contain iron were being treated or had been treated for anemia in the past 3 mo. The high prevalence of unexplained use of supplements containing iron by nonpregnant women suggested either that women did not interpret the question about treatment for anemia as we did or that use among nonpregnant women may be driven by factors other than clinically determined anemia.
Does supplement use prevent iron deficiency? We found that supplement use was associated with decreased prevalence of iron deficiency among nonpregnant, nonlactating women aged 19–50 y but not among older women. Older women may have a higher prevalence of chronic diseases that can affect iron status parameters beyond the association with iron supplement use. Among younger women and lactating women, the statistical power was inadequate to find meaningful differences in iron deficiency by supplement use.
Our assessment of supplement intake has some limitations. First, daily iron supplement intake was calculated using an indirect method that assumed that use over 1 mo could be applied to a single 24-h period. This calculation may not represent daily amounts for persons who do not take supplements consistently. The sample size was too small in some groups to find meaningful differences in prevalence. Nonresponse bias should be minimal because data for participants who received physical examinations in the mobile examination centers were adjusted by a nonresponse adjustment factor (14). Finally, these analyses were cross-sectional and, thus, causal conclusions cannot be made.
To meet national goals, we need to identify and pursue strategies that ensure appropriate screening and treatment for iron deficiency as well as improved iron intake and adherence to taking iron supplementation. Furthermore, we need to better understand the association among supplement use, iron deficiency and functional outcomes. We also need to understand the reasons for adherence, and lack thereof, to iron supplements, particularly among women at high risk of iron deficiency. We need to reevaluate requirements for iron among lactating women, particularly among women at high risk of iron deficiency. Finally, we need to better understand the absorption of iron in relation to other iron supplements, vitamins and minerals and dietary components.
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FOOTNOTES |
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2 Supported by the National Institutes of Health (HD-34531).
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LITERATURE CITED |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Centers for Disease Control and Prevention (1998) Recommendations to prevent and control iron deficiency in the United States. MMWR 47(rr-3):1-29.[Medline]
2. American Academy of Pediatrics American College of Obstetricians and Gynecologists (1997) Guidelines for perinatal care 4th edition. 1997 Elk Grove Village, IL .
3. U. S. Preventive Services Task Force (1993) Routine iron supplementation during pregnancy. JAMA 270:2846-2848.
4. Rasmussen, K. M. (2001) Is there a causal relationship between iron deficiency or iron deficiency anemia and weight at birth, length of gestation and perinatal mortality?. J. Nutr. 131:590S-603S].
5. Haas, J. D. & Brownlie, T. (2001) Iron deficiency and diminished work capacity: a critical review of the research to determine a causal relationship. J. Nutr. 131:676S-690S.
6. U. S. Department of Health and Human Services (November, 2000) Healthy People 2010. 2nd ed.. With Understanding and Improving Health and Objectives for Improving Health. 2 vols November, 2000 Government Printing Office Washington, DC: U. S.
7. Centers for Disease Control and Prevention (2002) Iron Deficiency—United States, 1999–2000. MMWR 51:897-899.[Medline]
8. National Center for Health Statistics (October, 2001) Healthy People 2000 Final Review October, 2001 U. S. Government Printing Office Hyattsville, Maryland: Public Health Service. Washington DC .
9. Centers for Disease Control and Prevention (1998) Pregnancy Nutrition Surveillance, 1996. Full report 1998 Health and Human Services, Centers for Disease Control and Prevention Atlanta, GA .
10. Bodnar, L., Cogswell, M. E. & Scanlon, K. S. (2002) Low income postpartum women are at risk of iron deficiency. J. Nutr. 132:2298-2302.
11. Enns, C. W., Goldman, J. D. & Cook, A. (1997) Trends in food and nutrient intakes by adults: NFCS 1977–78, CSFII 1989–91, and CSFII 1994–95. Family Econ. Nutr. Rev. 10:1-15.
12. Institute of Medicine (2001) Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc 2001 National Academy Press Washington DC .
13. Yu, S. M., Keppel, K. G., Singh, G. K. & Kessel, W. (1996) Preconceptional and prenatal multivitamin-mineral supplement use in the 1988 National Maternal and Infant Health Survey. Am. J. Public Health 86:240-242.
14. National Center for Health Statistics (1994) Plan and Operation of the Third National Health and Nutrition Examination Survey, 1988–94 1994 Vital and Health Statistics Hyattsville, MD 1(32).
15. U. S. Department of Agriculture (1987) Food and Nutrition Service Financial Management and Program Information Division. Annual Historical Review of FNS Programs: Fiscal Year 1987 1987 U. S. Department of Agriculture Washington, DC .
16. U. S. Bureau of the Census () Poverty in the United States: 1990. [Current population reports, 1991;175. Series P-60.] U. S. Bureau of the Census Washington, DC .
17. Gunter, E., Lewis, B. & Koncikowski, S. (1996) Laboratory procedures used for the third National Health and Nutrition Examination Survey (NHANES III) 1988–1994 1996 Centers for Disease Control and Prevention Hyattsville, MD .
18. Expert Scientific Working Group (1985) Summary of a report on assessment of the iron nutritional status of the United States population. Am. J. Clin. Nutr. 42:1318-1330.
19. Cook, J. D., Finch, C.A. & Smith, N. J. (1976) Evaluation of the iron status of a population. Blood 48:449-455.
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