Iron-Fortified vs Low-Iron Infant Formula Developmental Outcome at 10 Years

Abstract

Objective: To assess long-term developmental outcome in children who received iron-fortified or low-iron formula.

Design: Follow-up at 10 years of a randomized controlled trial (1991-1994) of 2 levels of formula iron. Examiners were masked to group assignment.

Setting: Urban areas around Santiago, Chile.

Participants: The original study enrolled healthy, fullterm infants in community clinics; 835 completed the trial. At 10 years, 473 were assessed (56.6%).

Intervention: Iron-fortified (mean, 12.7 mg/L) or low-iron (mean, 2.3 mg/L) formula from 6 to 12 months.

Main Outcome Measures: We measured IQ, spatial memory, arithmetic achievement, visual-motor integration, visual perception, and motor functioning. We used covaried regression to compare iron-fortified and low-iron groups and considered hemoglobin level before randomization and sensitivity analyses to identify 6-month hemoglobin levels at which groups diverged in outcome.

Results: Compared with the low-iron group, the iron-fortified group scored loweronevery 10-year outcome(significant for spatial memory and visual-motor integration; suggestive for IQ, arithmetic achievement, visual perception, and motor coordination; 1.4-4.6 points lower; effect sizes, 0.13-0.21). Children with high 6-month hemoglobin levels (>12.8 g/dL [to convert to grams per liter, multiply by 10]) showed poorer outcome on these measures if they received iron-fortified formula (10.7-19.3 points lower; large effect sizes, 0.85-1.36); those with low hemoglobin levels (<10.5 g/dL) showed better outcome(2.6-4.5 points higher; small but significant effects, 0.22-0.36). High hemoglobinlevels represented5.5% of the sample (n=26) and low hemoglobin levels represented 18.4% (n=87).

Conclusion: Long-term development may be adversely affected in infants with high hemoglobin levels who receive 12.7 mg/L of iron-fortified formula. Optimal amounts of iron in infant formula warrant further study.