Development and Validation of a Food Frequency Questionnaire for Assessing Dietary Calcium in Children

This study aimed to develop and validate a food frequency questionnaire (FFQ) for measuring calcium intake in 9-13 years old children in Tehran, Iran. A 56-item FFQ containing main contributors of calcium in Iranian diet was designed. Criterion validity of the calcium specific FFQ was evaluated through comparing its result with five 24-h recalls as the reference method. Reproducibility was measured by twice administration of FFQ, one month apart. The study was performed in the selected primary and middle schools of Tehran city. Subjects included 184 children aged 9-13 years (90 girls and 94 boys), who were recruited through two-stage systematic cluster sampling from 20 primary and middle schools. Mean calcium intake was 922.8±322.3 and 876.0±491.8 mg/d for the 24-h recalls and FFQ, respectively, indicating a mean difference of 46.7±458.7 mg/d (P<0.001). Corrected Pearson’s correlation was 0.57. Cross-classification analysis of the FFQ and 24-h recalls classified 80% of the subjects in the same or adjacent category, and 6% in the extreme quartiles. The FFQ correctly identified 85% of the children consuming less calcium than the age-specific Recommended Dietary Allowance (RDA) (1300 mg/d). Pearson’s correlation for repeated administrations was 0.65. Cross-classification analysis of the repeated administration of FFQ classified 81% of the subjects in the same or adjacent quartiles, and 3.3% in the extreme categories. The FFQ underestimates mean calcium intake of a group, and has limited use to estimate calcium intake for individuals. However, it has acceptable validity and reproducibility for epidemiologic studies to assess a group’s mean calcium intake.