Spontaneous motor activity in human infants with iron-deficiency anemia

Abstract

This study compared spontaneous motor activity in 6-month-old Chilean infants with or without iron-deficiency anemia (IDA) who were otherwise healthy. Activity was assessed in conjunction with polysomnographic recording during an afternoon nap in 11 infants with IDA and 15 with normal hemoglobin levels. All infants were given oral iron, and activity was reassessed at 12 and 18 months. Using actigraphs placed on the ankle, the frequency of movement units per minute was determined for each waking/sleep state. The total amount of time infants were in an alert–active state before and after the nap was used to calculate the proportion of movements/minute of waking. There were no differences between anemic and nonanemic infants in total recording time, duration of sleep, or motor activity during sleep. However, infants with IDA showed reduced motor activity during waking at all ages. The magnitude of the differences increased at 12 and 18 months. Thus, IDA was associated with reduced motor activity in infants even after iron treatment. It will be important to confirm these results in a larger sample and to determine the 24-h pattern of motor activity, since reduced motor activity may limit infants' opportunities to explore and learn from the social and physical environment.

Introduction

There is ample reason to suspect that iron-deficiency might alter spontaneous motor activity in infants. In rodents, iron-deficiency anemia (IDA) has been reported to reduce overall activity [1] and to alter the organization of its circadian pattern, including a total reversal [2], [3]. One study that systematically varied the timing of iron-deficiency during early development also found that iron-deficient rats moved less in a home-orienting task [4]. In the single study of motor activity in the iron-deficient primate—a small pilot project involving juvenile monkeys, even mild iron-deficiency anemia dramatically decreased running and playing [5]. In the adult human, iron-deficiency anemia and, in some cases, iron-deficiency without anemia reduce maximal physical performance, submaximal endurance, and work productivity (see reviews [6], [7], [8], [9], [10]). In school-aged children, the few published studies of iron-deficiency and motor activity report decreased activity [11], [12], [13]. Thus, evidence from animal models and studies of human children and adults indicates that iron-deficiency alters motor activity.

However, there is little information on this question in the iron-deficient human infant. The lack of research is striking, especially since infants and toddlers are among the groups at highest risk for iron-deficiency. Furthermore, in infancy, physical activity plays additional important roles in learning from the environment and in cognitive development [14]. To date, the only observations of activity in iron-deficient anemic infants are contained in a study of play behavior and mother–infant interaction. Using crude measures of activity (crossing gridlines in a playroom, moving beyond arm's length from the mother, etc.), the study's results suggested decreased activity [15].

The purpose of the present study was to assess the levels of spontaneous motor activity in infants with and without IDA. This pilot study was conducted in Chile and applied advanced methods of measuring activity in a controlled but ecologically valid situation–activity immediately before and after an afternoon nap. We hypothesized that IDA infants would demonstrate lower levels of motor activity compared to control infants.

Infant health is generally excellent in Chile, but iron-deficiency on a dietary basis has been common. Previous studies show that 27–35% of Chilean infants, including those solely breast fed, develop iron-deficiency anemia at 9–18 months of age, and biochemical evidence of iron-deficiency is present in 43–65% [17], [18]. Routine pediatric care and infant feeding practices in Chile during this study did not include iron supplementation.