Effects of iron deficiency in infancy on patterns of motor development over time
Introduction
There is renewed interest in the relationship between nutritional deficiencies in infancy and motor development (Kariger et al., 2005, Kuklina et al., 2004, Pollitt, 2000a). Although most previous studies on early nutritional deficiencies emphasize cognitive effects, the impact on motor development may be no less important. Adequate motor development is necessary for adequate visual-perceptual and cognitive development in infancy. Locomotion enables the infant to reach new objects and new places, opening opportunities for exploration, and has been shown to be critical for the development of visual perception (Adolph et al., 1993a, Adolph et al., 1993b) and spatial orientation (Acredolo, 1990). Sufficient fine motor control is required for effective object manipulation, through which infants develop their capabilities to process perceptual information. Indeed, a conceptual multi-level model of long-lasting intellectual delays in undernourished infants, developed by Pollitt and colleagues, postulates that poorer motor development is one of the first-level variables influencing cognitive outcome (Pollitt, 2000a, Pollitt et al., 2000, Walka and Pollitt, 2000).
Motor development also influences the infant’s independence and self-care, which can affect social-emotional attributes such as confidence and self-esteem. It has been shown, for example, that walking without assistance is followed by emotional changes reflecting autonomy and assertiveness and that infants become more sociable and affectionate after acquisition of walking skills (Biringen et al., 1995, Campos et al., 1992). Sufficient motor abilities are also important for adequate development of social skills during early childhood as children socialize through play. In early childhood, play is based mostly on interactions through and during physical activity. Furthermore, motor development during childhood may provide the foundation for subsequent development of occupational performance in adulthood and ability to enjoy and participate in social leisure activities that involve motor skills (e.g., sports, dancing, etc.).
This study focused on iron deficiency (ID), the most common nutrient deficiency in the world. In developing countries 46–66% of children under four years are anemic, with half attributed to ID (Stoltzfus, Mullany, & Black, 2004). A number of studies have reported lower motor development scores for infants with IDA or other indication of chronic severe ID, compared to infants with good iron status. Thirteen such studies from countries around the world assessed otherwise healthy 6- to 24-month-old infants using a standardized motor test (Akman et al., 2004, Antunes, 2004, Driva et al., 1985, Hasanbegovic and Sabanovic, 2004, Hokama et al., 2005, Idjradinata and Pollitt, 1993, Johnson and McGowan, 1983, Lozoff et al., 1982, Lozoff et al., 1987, Lozoff et al., 1996, Shafir Liberzon et al., 2005, Walter et al., 1989, Walter et al., 1983). Eight of them found IDA infants to have lower motor scores (Akman et al., 2004, Hasanbegovic and Sabanovic, 2004, Hokama et al., 2005, Idjradinata and Pollitt, 1993, Lozoff et al., 1982, Lozoff et al., 1987, Shafir Liberzon et al., 2005, Walter et al., 1989). In addition, in a British population study, low hemoglobin (Hb) concentration (⩽95 g/L) in 8-month-old infants was associated with poorer motor development at 18 months (Sherriff, Emond, Bell, Golding, & Alspac, 2001). Similarly, IDA infants at risk for stunting showed poorer motor development. For instance, IDA infants walked later in two recent studies in Nepal and Zanzibar (Kariger et al., 2005, Siegel et al., 2005).
Several of these studies sought to demonstrate an effect of ID on motor development by showing improvement after a full course of iron therapy (⩾3 months). Seven studies used standardized tests and are sufficiently similar for comparison (Akman et al., 2004, Antunes, 2004, Hasanbegovic and Sabanovic, 2004, Idjradinata and Pollitt, 1993, Lozoff et al., 1987, Lozoff et al., 1996, Walter et al., 1989). Four reported that lower motor scores persisted in IDA infants (Hasanbegovic and Sabanovic, 2004, Lozoff et al., 1987, Lozoff et al., 1996, Walter et al., 1989), whereas the other three observed improvements (Akman et al., 2004, Antunes, 2004, Idjradinata and Pollitt, 1993). Although the reasons for the differing results are still unknown, pretreatment scores were much lower in IDA infants in the studies that showed improvement, compared to those that did not.
There are also 10 randomized controlled trials of iron supplementation (or placebo), regardless of initial iron status. Among preventive trials with healthy full-term infants in the 6–24 month range, one in Canada showed lower motor scores at 9 and/or 12 months in the group that did not receive prophylactic iron (Moffatt, Longstaffe, Besant, & Dureski, 1994). A large study in Chile (n = 1657) found that infants who did not receive iron crawled somewhat later and more were rated as tremulous (Lozoff et al., 2003). A small randomized controlled trial involving breast-fed infants in Canada showed a benefit of even earlier iron supplementation. Infants who received iron between 1 and 6 months had better motor scores at 12 months, compared to those receiving placebo (Friel et al., 2003). Two preventive trials with healthy term infants did not show motor effects (Morley et al., 1999, Williams et al., 1999).
In addition to the Chile study, there are four other large, recent supplementation trials in developing countries. They involved infants at risk for stunting (Black et al., 2004, Black et al., 2002, Lind et al., 2004) often assessing iron with or without other micronutrients. All showed benefits of supplemental iron on motor development.
Although the majority of studies have found effects of ID on motor development during infancy, there are only two samples in which long-term motor effects were assessed. Follow-up studies of a Costa Rica sample showed that children who had severe, chronic ID during infancy scored lower on the Bruininks-Oseretsky Test of Motor Proficiency at 5 years and during early adolescence (Lozoff et al., 2000, Lozoff et al., 1991). In a follow-up study in Chile, 5.5-year-old children who had IDA during their first year of life also scored lower on the Bruininks-Oseretsky than children who did not have IDA during infancy (De Andraca et al., 1991). These long-lasting differences, however, do not answer questions about changes in motor development over time. For instance, do children treated for ID in infancy show some evidence of catch up or do they show a widening gap in motor performance? Do their patterns of motor development differ from those of children without ID in infancy? We report here the use of longitudinal analysis (hierarchical linear modeling) to study the effect of ID in infancy on motor development over time.
Section snippets
Sample
This longitudinal analysis was based on the Costa Rica sample mentioned above. Costa Rica is a Central American country with an excellent record of infant health, but iron supplementation was not routinely recommended at the time the study started. The analysis used the children’s iron status measurements and motor development assessments before and after 3 months of iron treatment during infancy, and follow-up motor assessments at 5 years and 11–14 years. All aspects of the research were
Results
There was evidence of a modest degree of stability in relative motor scores from infancy to later ages in this sample. Overall, the correlations between PDI scores and Bruininks-Oseretsky scores at 5 and 11–14 years ranged from .19 to .41 (p values all <.02). The longitudinal (hierarchical linear modeling or mixed model) analysis showed significant differences depending on gender and iron status in infancy. The longitudinal trajectories for males differed from females in slope and quadratic
Discussion
In this study of the effects of ID in infancy on motor development over time, children who had chronic ID in infancy had lower motor scores than children with good iron status, statistically significant at all ages. Mean scores of the chronic ID group were at the lower end of the range considered ‘normal’ (mean ±1 SD), and more of them had scores more than 1 SD below the US norm at each age. In longitudinal analysis, boys in the chronic ID group continued to have scores at the low end of the
Acknowledgements
Supported by grants from the National Institutes of Health (R01 HD31606 and a MERIT Award to B. Lozoff, R37 HD31606). Preliminary results were presented at the Ambulatory Pediatrics Association Presidential Plenary Session, Pediatric Academic Societies meetings, San Francisco, May 3, 2004, and at the North American Society for Psychology of Sport and Physical Activity annual meetings, Vancouver, British Columbia, June 12, 2004. We are thankful to the study participants and their families for
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Cited by (0)
- 1
Currently at Rho Inc., Chapel Hill, North Carolina.
- 2
Currently at Hospital CIMA-San Jose, Costa Rica.