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

Abstract

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.

Figure 1

Flow chart of study participation. The number (%) of participants at each time point is shown, indicating that participants who missed an assessment were often available subsequently.

Figure 2

Cognitive composite scores over time, comparing infant iron status groups within middle and low socio-economic status (SES) families. Iron status group and SES level each affected initial scores (P values < .01). Change over time differed only for the chronic-iron-deficiency group in low-SES families (P < .05). Each participant is represented once: good iron status (n = 67) compared to chronic iron deficiency (n = 20) in middle-SES families and good iron status (n = 65) compared to chronic iron deficiency (n = 33) in low-SES families. Symbols are placed at the average age for each assessment.