The purpose and procedures of the study were explained to
parents or caretakers of children in grades 3–5. Almost all parents
allowed their children to participate and signed an informed
consent form. As in our previous study (5), we selected anemic
subjects because serum retinol concentrations are correlated with
hemoglobin concentrations (6). Thus, children (n = 1231) were
screened initially on the basis of their hemoglobin concentration
(Hemocue, Angelholm, Sweden) and hematocrit value, determined
from a finger-prick blood sample