Double burden of iron deficiency in infancy and low socioeconomic status: a longitudinal analysis of cognitive test scores to age 19 years.

OBJECTIVE To assess change in cognitive functioning after iron deficiency in infancy, depending on socioeconomic status (SES; middle vs low). DESIGN Longitudinal study. SETTING Urban community in Costa Rica (infancy phase [July 26, 1983, through February 28, 1985] through 19-year follow-up [March 19, 2000, through November 4, 2002]). PARTICIPANTS A total of 185 individuals enrolled at 12 to 23 months of age (no preterm or low-birth-weight infants or infants with acute or chronic health problems). The participants were assessed in infancy and at 5, 11 to 14, 15 to 18, and 19 years of age. A total of 97% were evaluated at 5 or 11 to 14 years and 78% at 15 to 18 or 19 years. Individuals who had chronic iron deficiency in infancy (iron deficiency with hemoglobin concentrations < or =10.0 g/dL or, with higher hemoglobin concentrations, not fully corrected within 3 months of iron therapy) were compared with those who had good iron status as infants (hemoglobin concentrations > or =12.0 g/dL and normal iron measures before and/or after therapy). MAIN OUTCOME MEASURES Cognitive change over time (composite of standardized scores at each age). RESULTS For middle-SES participants, scores averaged 101.2 in the group with chronic iron deficiency vs 109.3 in the group with good iron status in infancy and remained 8 to 9 points lower through 19 years (95% confidence interval [CI], -10.1 to -6.2). For low-SES participants, the gap widened from 10 points (93.1 vs 102.8; 95% CI for difference, -12.8 to -6.6) to 25 points (70.4 vs 95.3; 95% CI for difference, 20.6 to 29.4). CONCLUSIONS The group with chronic iron deficiency in infancy did not catch up to the group with good iron status in cognitive scores over time. There was a widening gap for those in low-SES families. The results suggest the value of preventing iron deficiency in infancy.