Assessing zinc and iron deficiency in preschool children

Nutrition Research Newsletter, April, 2006

Inadequate intakes of iron and zinc by children are associated with developmental delays, behavioral changes, and an increased risk of infectious diseases. Due to these risks, one current national health objective (Healthy People 2010 objective 19-12) is to reduce iron deficiency to 1% among preschool children. The Third National Health and Nutrition Examination survey (1988-1994) data set suggests the US preschool children consume insufficient zinc. Only 18.9% of one-to-three-year old and 51.5% of four-to-six-year old children had adequate zinc intake. Insufficient intakes of iron and zinc are of particular concern in low-income preschool children in the United States.

Determining micronutrient status can be difficult in the presence of infection. Plasma zinc and ferritin are two measures commonly used to assess zinc and iron status; however, the changes with infection could result in misclassification of micronutrient status. Given the high rates of infection in preschool children, the potential for misclassification of micronutrient status may be quite high and contribute to less effective intervention programs. In order to decrease the changes of misclassification and increase the effectiveness of interventions, the relations among indicators of infection and micronutrient status need to be clarified in this age group.

It was recently reported the importance of reporting elevations of acute-phase proteins (produced in response to infection) to better assess micronutrient status. In a number of other studies C-reactive protein (CRP) and total and differential leukocyte counts have shown promise as potential quantifiers of the effects of infection on indicators of micronutrient status. Utilization of multiple measures of infection appears to be more informative.

Therefore, the purpose of the recent study was to evaluate the relations among commonly used indicators of infection and micronutrient status, the percentage of low-income, rural preschool children with micronutrient deficiencies, and the number of elevated indicators associated with differences in zinc and iron status. Forty-seven three-to-five-year old children, who attended Head Start in three communities in rural north-central Oklahoma, served as subjects. The study employed a cross-sectional correlation design.

Each Head Start center offered breakfast to all children prior to venous blood samples being collected. Blood was analyzed for complete blood cell counts and red blood cell indexes. Serum CRP was measured on an ACE analyzer. Plasma zinc was measured. Zinc concentrations and serum ferritin were also measured.

Most (72%) of the children had elevated CRP levels. 4% were anemic (hemoglobin < 11.0 g/dL); 11% had low iron stores (serum ferritin d" 15 ng/mL); and 77% had low-iron stores when a reference value that accounts for the presence of infection was used (serum ferritin d" 30 ng/mL). 21% had low-plasma zinc levels. Children with two measures that indicated infection had higher serum ferritin and lower plasma zinc levels than children with zero or one indicator of infection.

The relationship between measures of infection and serum ferritin levels suggests low-income preschool children with low iron stores are not identified by the d" 15 hg/mL (d" 33.7 pmol/L) criterion. The link between zinc and infection suggests possible overestimations of zinc deficiency in low-income children. Investigators suggest that in this population, the presence of infection (as indicated by CRP levels and leukocyte counts) should be determined to assess micronutrient status.

E. Droke, T. Kennedy, L. Hubbs-Tait, et al. Potential for misclassification of micronutrient status in children participating of micronutrient status in children participating in a Head Start program. J Am Diet Assoc; 106:376-382 (March, 2006) [Correspondence: Elizabeth A. Droke, PhD, RD, Department of Nutrition, Food Science, and Hospitality, Box 2275A, NFA 425 Rotunda Ln, South Dakota State University, Brookings, SD 57007. E-mail: Elizabeth.droke@sdstate.edu]