SERUM BONE GAMMA-CARBOXYGLUTAMIC ACID PROTEIN IN A LONGITUDINAL-STUDYOF INFANTS - LOWER VALUES IN FORMULA-FED INFANTS

Bone gamma-carboxyglutamic acid protein [BGP (osteocalcin)] is a prote in synthesized by osteoblasts and incorporated in the bone matrix. Ser um BGP is a sensitive marker of bone formation, and it parallels the g rowth velocity curve during childhood and adolescence. Serum BGP was m easured at the age of 2, 6, and 9 mo in a cohort study of nutrition an d growth in 91 healthy infants. At 2 mo, the mean BGP value (+/- SD) w as 275 +/- 87 ng/mL in infants exclusively breast-fed, and 80 +/- 44 n g/mL in formula-fed infants. At 6 mo, the values were 142 +/- 58 ng/mL and 55 +/- 30 ng/mL, and at 9 mo 75 +/- 39 ng/mL and 45 +/- 19 ng/mL in partially breast-fed and formula-fed infants, respectively. The dif ferences were significant (p < 0.001) at all three ages. At 2 and 9 mo , breast-milk intake was measured by test-weighing. Serum BGP was posi tively correlated to breast milk intake (mL/kg body wt) at 2 mo (r = 0 .59, p < 0.001 ) and 9 mo (r = 0.41, p = 0.06). When breast-feeding wa s stopped, the high BGP concentrations were not sustained. There were no significant differences in linear growth velocity between breast-fe d and formula-fed infants and no correlation between BGP values and li near growth velocity. We speculate that either a factor in human milk or the level of minerals in human milk causes the high BGP values. Mor eover, if the higher values are associated with increased osteoblast a ctivity, then the remodeling or the mineralization of bone might be di fferent in infants not being breast-fed.