RESEARCH Research and Professional Briefs
Iron Deficiency Is Associated with Food Insecurity in Pregnant Females in the United States: National Health and Nutrition Examination Survey 1999-2010 Clara Y. Park, PhD; Heather A. Eicher-Miller, PhD ARTICLE INFORMATION
ABSTRACT
Article history:
Food-insecure pregnant females may be at greater risk of iron deficiency (ID) because nutrition needs increase and more resources are needed to secure food during pregnancy. This may result in a higher risk of infant low birth weight and possibly cognitive impairment in the neonate. The relationships of food insecurity and poverty income ratio (PIR) with iron intake and ID among pregnant females in the United States were investigated using National Health and Nutrition Examination Survey 1999-2010 data (n¼1,045). Food security status was classified using the US Food Security Survey Module. One 24-hour dietary recall and a 30-day supplement recall were used to assess iron intake. Ferritin, soluble transferrin receptor, or total body iron classified ID. Difference of supplement intake prevalence, difference in mean iron intake, and association of ID and food security status or PIR were assessed using c2 analysis, Student t test, and logistic regression analysis (adjusted for age, race, survey year, PIR/food security status, education, parity, trimester, smoking, C-reactive protein level, and health insurance coverage), respectively. Mean dietary iron intake was similar among groups. Mean supplemental and total iron intake were lower, whereas odds of ID, classified by ferritin status, were 2.90 times higher for food-insecure pregnant females compared with food-secure pregnant females. Other indicators of ID were not associated with food security status. PIR was not associated with iron intake or ID. Food insecurity status may be a better indicator compared with income status to identify populations at whom to direct interventions aimed at improving access and education regarding iron-rich foods and supplements.
Accepted 24 April 2014 Available online 20 June 2014
Keywords: Iron deficiency Pregnancy Food security Iron intake National Health and Nutrition Examination Survey (NHANES) 2212-2672/Copyright ª 2014 by the Academy of Nutrition and Dietetics. http://dx.doi.org/10.1016/j.jand.2014.04.025
J Acad Nutr Diet. 2014;114:1967-1973.
I
RON DEFICIENCY (ID) IS ONE OF THE MOST COMMON nutritional deficiencies. Among pregnant females in the United States, 16.1% were ID during 2003-2006.1 Low maternal iron status is correlated with low and verylow infant birth weight,2,3 preterm birth,4 and low infant iron stores.5,6 Low iron status during infancy has been linked with learning and memory deficits and mental retardation. 7-9 Accordingly, the World Health Organization recommends iron supplementation10 and the Healthy People 2020 objectives include the reduction of ID status11 among pregnant females. Despite the greater iron needs during pregnancy,12 females in this life stage may have less energy and ability to prepare foods due to physical constraints. Pregnancy may also increase financial burden because greater energy and nutrients are necessary to support the pregnancy and decreased or refrained employment may occur. This may exacerbate the difficulties food-insecure pregnant females face to meet their nutrition needs and may incur food
ª 2014 by the Academy of Nutrition and Dietetics.
insecurity among females who were food secure preceding pregnancy. Alternatively, pregnant females might be protected from nutritional deficits related to food insecurity by the prioritized receipt of nutritious food and supplements within the household. Few studies investigating the relationship of food insecurity, iron intake, and ID have been documented among pregnant females. Previous research completed among children,13,14 women with children,15 and elderly persons15,16 have shown greater likelihood for ID anemia and lower iron intakes among food-insecure compared with food-secure groups. Among pregnant women living in North Carolina, food insecurity was not associated with anemia,17 but the relationships of food security to iron intake and status have not been described for all US pregnant females. Although the lack of access to food might facilitate the relationship of food insecurity to low iron intake and status among food-insecure groups, the low purchasing ability of
JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS
1967
RESEARCH those with a reduced household poverty income ratio (PIR) may facilitate a relationship to low iron intake and status among groups with low PIR. Food-insecure and reduced-PIR groups are similar but may comprise slightly different populations, resulting in the mixed findings describing the relationship of PIR to iron intake and status in previous studies.18-22 Therefore, both food insecurity and PIR were examined in our study using a hypothesis that food-insecure pregnant females in the United States have lower iron intake from food, beverages, and supplements and higher odds of ID compared with food-secure pregnant females. In addition, the hypothesis that pregnant females in the United States with low PIR status have lower iron intake from diet and supplements and higher odds of ID compared to those with higher PIR status was also tested.
SUBJECTS AND METHODS Study Population National Health and Nutrition Examination Survey (NHANES) data collected during 1999-2010 were used. NHANES provides a cross-sectional representation of the health status and nutrition-related behaviors of noninstitutionalized civilian residents of the United States. Oversampling was performed for pregnant females during 1999-2006.23-26 The study population was limited to participants with a positive urine pregnancy test that was performed at the mobile examination center (MEC) (n¼1,383). Pregnant females missing food security status (n¼53), Day 1 24-hour dietary recall (n¼42), iron status (n¼85), or family PIR status (n¼69), and those whose race was not categorized as non-Hispanic white, non-Hispanic black, or Hispanic (n¼69) were excluded. A total of 1,045 females were included (aged 13 to 54 years). The National Center for Health Statistics Research Ethics Review Board approved the protocol for all NHANES content.27
Dietary Assessment Dietary iron and energy intake information was obtained from the 24-hour dietary recall.28,29 Mean daily supplemental iron intake was calculated from the 30-day dietary supplement questionnaire.30,31 Total iron intake was determined as the sum of 24-hour dietary iron intake and mean daily supplemental iron intake. Only participants with complete information of iron supplement use or selfreported nonusers were included to calculate the mean daily iron supplement intake and total iron intake. Categorical variables for dietary iron intake were created as less than or greater than or equal to the Estimated Average Requirement (EAR) for pregnant females (aged 14 to 18 years: 23 mg/day; aged 19 to 50 years: 22 mg/day32). Energy intake was categorized (ie, 2,800 kcal/day).
Iron Status Assessment and Other Laboratory Examinations Serum ferritin was assessed by immunoturbidimetric (NHANES 1999-2002 and 2004-2008), immunoradiometric (NHANES 2003), or sandwich immunoassay (NHANES 20092010) and adjusted for comparability.33,34 Details of analyses 1968
JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS
of soluble transferrin receptor (sTfR), hemoglobin, and hematocrit are provided elsewhere.23-26,35 Total body iron (TBI) calculations were computed using the equation developed by Cook and colleagues.36,37 An equation was used to adjust sTfR obtained through the Roche method (used by NHANES) to values equivalent to the Flowers method (used by Cook and colleagues).19,38,39 Afterward, TBI was calculated as: TBIðmg=kgÞ¼½log10ðsTfR1;000=ferritinÞ2:8229=0:1207 Iron deficiency was recognized if TBI 4.4 mg/L,19,40 or ferritin 5 mg/L.19 Comparison between food-secure females and food-insecure females among those without inflammation present, indicated by CRP 5 mg/L, was not possible due to the inadequate sample size of food-insecure females (n¼66).
Food Security Assessment and Classification of Other Characteristics Food security was assessed using the US Food Security Survey Module. During NHANES 1999-2002, the questionnaire was administered as part of the household interview to one adult to classify food security among household adults or children. Individual-level food security status was determined at the MEC since 2001 for adults (aged 16 years) and children (aged
Iron Deficiency Is Associated with Food Insecurity in Pregnant Females in the United States: National Health and Nutrition Examination Survey 1999-2010 Clara Y. Park, PhD; Heather A. Eicher-Miller, PhD ARTICLE INFORMATION
ABSTRACT
Article history:
Food-insecure pregnant females may be at greater risk of iron deficiency (ID) because nutrition needs increase and more resources are needed to secure food during pregnancy. This may result in a higher risk of infant low birth weight and possibly cognitive impairment in the neonate. The relationships of food insecurity and poverty income ratio (PIR) with iron intake and ID among pregnant females in the United States were investigated using National Health and Nutrition Examination Survey 1999-2010 data (n¼1,045). Food security status was classified using the US Food Security Survey Module. One 24-hour dietary recall and a 30-day supplement recall were used to assess iron intake. Ferritin, soluble transferrin receptor, or total body iron classified ID. Difference of supplement intake prevalence, difference in mean iron intake, and association of ID and food security status or PIR were assessed using c2 analysis, Student t test, and logistic regression analysis (adjusted for age, race, survey year, PIR/food security status, education, parity, trimester, smoking, C-reactive protein level, and health insurance coverage), respectively. Mean dietary iron intake was similar among groups. Mean supplemental and total iron intake were lower, whereas odds of ID, classified by ferritin status, were 2.90 times higher for food-insecure pregnant females compared with food-secure pregnant females. Other indicators of ID were not associated with food security status. PIR was not associated with iron intake or ID. Food insecurity status may be a better indicator compared with income status to identify populations at whom to direct interventions aimed at improving access and education regarding iron-rich foods and supplements.
Accepted 24 April 2014 Available online 20 June 2014
Keywords: Iron deficiency Pregnancy Food security Iron intake National Health and Nutrition Examination Survey (NHANES) 2212-2672/Copyright ª 2014 by the Academy of Nutrition and Dietetics. http://dx.doi.org/10.1016/j.jand.2014.04.025
J Acad Nutr Diet. 2014;114:1967-1973.
I
RON DEFICIENCY (ID) IS ONE OF THE MOST COMMON nutritional deficiencies. Among pregnant females in the United States, 16.1% were ID during 2003-2006.1 Low maternal iron status is correlated with low and verylow infant birth weight,2,3 preterm birth,4 and low infant iron stores.5,6 Low iron status during infancy has been linked with learning and memory deficits and mental retardation. 7-9 Accordingly, the World Health Organization recommends iron supplementation10 and the Healthy People 2020 objectives include the reduction of ID status11 among pregnant females. Despite the greater iron needs during pregnancy,12 females in this life stage may have less energy and ability to prepare foods due to physical constraints. Pregnancy may also increase financial burden because greater energy and nutrients are necessary to support the pregnancy and decreased or refrained employment may occur. This may exacerbate the difficulties food-insecure pregnant females face to meet their nutrition needs and may incur food
ª 2014 by the Academy of Nutrition and Dietetics.
insecurity among females who were food secure preceding pregnancy. Alternatively, pregnant females might be protected from nutritional deficits related to food insecurity by the prioritized receipt of nutritious food and supplements within the household. Few studies investigating the relationship of food insecurity, iron intake, and ID have been documented among pregnant females. Previous research completed among children,13,14 women with children,15 and elderly persons15,16 have shown greater likelihood for ID anemia and lower iron intakes among food-insecure compared with food-secure groups. Among pregnant women living in North Carolina, food insecurity was not associated with anemia,17 but the relationships of food security to iron intake and status have not been described for all US pregnant females. Although the lack of access to food might facilitate the relationship of food insecurity to low iron intake and status among food-insecure groups, the low purchasing ability of
JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS
1967
RESEARCH those with a reduced household poverty income ratio (PIR) may facilitate a relationship to low iron intake and status among groups with low PIR. Food-insecure and reduced-PIR groups are similar but may comprise slightly different populations, resulting in the mixed findings describing the relationship of PIR to iron intake and status in previous studies.18-22 Therefore, both food insecurity and PIR were examined in our study using a hypothesis that food-insecure pregnant females in the United States have lower iron intake from food, beverages, and supplements and higher odds of ID compared with food-secure pregnant females. In addition, the hypothesis that pregnant females in the United States with low PIR status have lower iron intake from diet and supplements and higher odds of ID compared to those with higher PIR status was also tested.
SUBJECTS AND METHODS Study Population National Health and Nutrition Examination Survey (NHANES) data collected during 1999-2010 were used. NHANES provides a cross-sectional representation of the health status and nutrition-related behaviors of noninstitutionalized civilian residents of the United States. Oversampling was performed for pregnant females during 1999-2006.23-26 The study population was limited to participants with a positive urine pregnancy test that was performed at the mobile examination center (MEC) (n¼1,383). Pregnant females missing food security status (n¼53), Day 1 24-hour dietary recall (n¼42), iron status (n¼85), or family PIR status (n¼69), and those whose race was not categorized as non-Hispanic white, non-Hispanic black, or Hispanic (n¼69) were excluded. A total of 1,045 females were included (aged 13 to 54 years). The National Center for Health Statistics Research Ethics Review Board approved the protocol for all NHANES content.27
Dietary Assessment Dietary iron and energy intake information was obtained from the 24-hour dietary recall.28,29 Mean daily supplemental iron intake was calculated from the 30-day dietary supplement questionnaire.30,31 Total iron intake was determined as the sum of 24-hour dietary iron intake and mean daily supplemental iron intake. Only participants with complete information of iron supplement use or selfreported nonusers were included to calculate the mean daily iron supplement intake and total iron intake. Categorical variables for dietary iron intake were created as less than or greater than or equal to the Estimated Average Requirement (EAR) for pregnant females (aged 14 to 18 years: 23 mg/day; aged 19 to 50 years: 22 mg/day32). Energy intake was categorized (ie, 2,800 kcal/day).
Iron Status Assessment and Other Laboratory Examinations Serum ferritin was assessed by immunoturbidimetric (NHANES 1999-2002 and 2004-2008), immunoradiometric (NHANES 2003), or sandwich immunoassay (NHANES 20092010) and adjusted for comparability.33,34 Details of analyses 1968
JOURNAL OF THE ACADEMY OF NUTRITION AND DIETETICS
of soluble transferrin receptor (sTfR), hemoglobin, and hematocrit are provided elsewhere.23-26,35 Total body iron (TBI) calculations were computed using the equation developed by Cook and colleagues.36,37 An equation was used to adjust sTfR obtained through the Roche method (used by NHANES) to values equivalent to the Flowers method (used by Cook and colleagues).19,38,39 Afterward, TBI was calculated as: TBIðmg=kgÞ¼½log10ðsTfR1;000=ferritinÞ2:8229=0:1207 Iron deficiency was recognized if TBI 4.4 mg/L,19,40 or ferritin 5 mg/L.19 Comparison between food-secure females and food-insecure females among those without inflammation present, indicated by CRP 5 mg/L, was not possible due to the inadequate sample size of food-insecure females (n¼66).
Food Security Assessment and Classification of Other Characteristics Food security was assessed using the US Food Security Survey Module. During NHANES 1999-2002, the questionnaire was administered as part of the household interview to one adult to classify food security among household adults or children. Individual-level food security status was determined at the MEC since 2001 for adults (aged 16 years) and children (aged
