Postnatal development of bone mineral status during infancy

Objective: To determine postnatal development in bone mineral status and its relationship to anthropometric measurements and other physiologic variables during the first year. Methods: Cross-section observational study of total body bone mineral content (TB BMC) and density (TB BMD) of 130 healthy infants (71 male and 59 female with 63 white and 67 African American) between 1 and 391 days. Whole body dual energy X ray absorptiometry (DXA) scans were performed on unsedated infants using a bone densitometer with pediatric platform. Scan analyses were performed with software version V5.64P. The ability of study independent variables to explain variance in bone mineral status was determined by multiple linear regression analysis. Results: During infancy, average TB BMC increased by 389% and TB BMD increased by 157%. The best determinant of bone mineral status is body weight which accounted for 97% of TB BMC, 98% of TB area and 86% of TB BMD variation. Postnatal age and body length jointly added only 1%, <1% and 2.5%, respectively, to the explained variation of these DXA measurements; race, gender and season all failed to reach statistical significance. Conclusion: In healthy infants, body weight is the dominant predictor of bone mineral status. The percent increase in TB BMC differs from increase in TB BMD. Normative data generated from this study would be useful in the identification of abnormal bone mineral status in infants.