Effect of physical activity on bone mineralization in premature infants,☆☆,,★★

Presented in part at the Western Society for Pediatric Research, Carmel, Calif., 1995; abstract published in the Journal of Clinical Investigation, 1995.
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Abstract

Objective: A 4-week pilot study was done with 26 preterm infants to evaluate whether a physical activity program would result in greater bone mineralization. Design: Subjects were matched by birth weight, gender, and gestational age, and randomly assigned to the physical activity program (group EX; n = 13) or to the control group (group C; n = 13). Physical activity consisted of range of motion with passive resistance to all extremities for 5 to 10 minutes daily. Baseline and 4-week values were determined for both bone mineral analyses and serum levels of calcium, phosphate, alkaline phosphatase, parathyroid hormone, and 25-hydroxyvitamin D. Results: Despite similar nutrient intake at advised levels for preterm infants, EX infants gained more weight than control subjects (17.8 vs 13.4 gm/kg body weight per day; p = 0.01). A difference in radial bone mass and density change as determined by single-beam photon absorptiometry (±2% error) was found between groups (p = 0.006 by analysis of covariance). Changes in bone width and in bone mineral content and density were enhanced by physical activity. Group EX infants had 12%, 18%, and 34% gains in bone width and in bone mineral density and content, respectively; group C infants had only a 2% gain in bone width and 11% and 14% losses from baseline in bone mineral content and density, respectively, during the 4-week study. Serum biochemical values were similar in the groups except for lower alkaline phosphatase levels in group EX. There was a negative association between bone mineral content and parathyroid hormone values: r = −0.83, p = 0.01. Conclusions: A physical activity program may increase the effects of adequate nutrition in healthy preterm very low birth weight infants by promoting weight gain and bone mass and by decreasing the risk of osteopenia. (J PEDIATR 1995;127:620-5)

Section snippets

STUDY DESIGN

Subjects consisted of healthy premature infants recruited from the newborn intensive care unit at the University Hospital, Salt Lake City, Utah. Subjects were eligible for study under the following criteria: gestational age range of 26 to 34 weeks, appropriate body size, ability to tolerate enteral feedings at ≥110 kcal/kg body weight per day, absence of medications other than appropriate vitamin supplements, and informed parental consent. Subjects were removed from the study for incomplete

RESULTS

Forty-nine infants were initially considered for study after informed parental consent was obtained. Of the 49 infants, 23 (45%) were dropped from the study because of incomplete data resulting from hospital discharge or transfer before a minimum of 28 study days. Twenty-six infants completed the 4-week study, with 13 infants assigned to each group. There were no differences in gestational age, birth weight, length, head circumference, gender, ethnicity, or feeding choice between groups at

DISCUSSION

Preterm infants frequently have osteopenia;24, 25 clinical symptoms range from mild demineralization to nontraumatic fracture. Osteopenia develops in premature infants when the intake of mineral substrate is inadequate for maintenance of normal bone growth and development. However, dietary intake of bone mineral substrates, specifically calcium, phosphorus, magnesium, and protein, is only one factor in growth and development of healthy bone. Other factors that influence bone growth and bone

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    From the Departments of Pediatrics and Exercise and Sport Science, University of Utah, Salt Lake City, Utah

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    Supported in part by Public Health Services research grant No. MO1-RR00064 from the National Center for Research Resources.

    Reprint requests: Laurie Moyer-Mileur, PhD, RD,CD, 2A210, Division of Neonatology, University of Utah, Salt Lake City, UT 84132.

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