Effect of timing of introduction of complementary foods on iron and zinc status of formula fed infants at 21, 24, and 36 months of age

Objective The timing of introduction of complementary food to an infant's d iet is variable throughout the world. Our objective was to determine whethe r early introduction of complementary foods affects iron and zinc status of formulated infants at 12, 24, and 36 months of age. Design A randomized, prospective trial was conducted. Infants were randomly assigned to receive either a) early introduction (at 3 to 4 months of age) of commercially prepared or parent's choice of complementary foods; or b) late introduction (at 6 months of age) of commercially prepared complementa ry foods or parent's choice of complementary foods. In addition to compleme ntary foods, infants were fed commercial infant formula as recommended by t heir pediatrician. Hemoglobin, mean corpuscular volume, and serum ferritin and zinc concentrations were determined at 12, 24, and 36 months of age. Th ree-day diet diaries were completed at 3, 6, 12, 18, 24, 30, and 36 months of age. Subjects/setting One hundred seventy-five infants younger than 3 months wer e recruited by mailings to parents in the Cincinnati area. Of these, 172 we re enrolled, 90 in the early-introduction group and 82 in the late-introduc tion group. One hundred thirty-three infants (n=67 in the early, n=66 in th e late group) completed the study, Statistical analyses performed Student t test and regression analyses were used to determine whether there were group differences and whether there wa s a relationship between serum parameters and dietary intake. Results Infants fed complementary foods early had significantly greater iro n intakes until 6 months of age; however, there were no differences in the iron status parameters (ferritin, hemoglobin, and mean corpuscular volume) at 12, 24, or 36 months of age. The early introduction group consumed sligh tly less zinc than the late introduction group at 5 months (4.4 vs 4.8 mg/d ay, P < .01) and 6 months (4.4 vs 4.7 mg/day, P < .01). At all other times there were no differences between the early and late group in zinc intakes. The serum zinc concentration was not associated with dietary zinc. Both gr oups had normal serum zinc concentrations at 12, 24, and 36 months and ther e were no differences between groups. Applications/conclusions The iron and zinc status of infants in this study was not influenced by the timing or type of complementary foods introduced. However, the infants were formula fed and the mean iron and zinc intakes t hat were equal or greater than the Recommended Dietary Allowances for the f irst 6 months of age.