RESUMEN
BACKGROUND: Early infant feeding can affect skeletal development. Most children are fed with breast milk, dairy-based infant formula, or soy-based infant formula during the first year of life. The National Health and Nutrition Examination Survey 2003-2010 reports that 12% of the US infants consume soy-based infant formula. Despite potential effects of soy-associated isoflavones on skeletal development, studies investigating bone metabolism and structural and functional bone indices in children are lacking. OBJECTIVE: The aim of this observational study was to investigate early effects of soy-based infant formula (SF group) intake on bone metabolism and structure during the first 6 y of life comparing with those of infants fed with breast milk (BF group) and dairy-based infant formula (MF group). METHODS: A total of 433 healthy infants were followed up from 3 mo to 6 y of age. Children's skeletal development was assessed using dual-energy X-ray absorptiometry (DXA; N = 433) and peripheral quantitative computed tomography (pQCT; n = 78). The urinary biomarkers of bone metabolism (N-terminal telopeptide of type I collagen [NTx] and osteocalcin) were evaluated using immunoassays at 6, 24, 60, and 72 mo. RESULTS: No statistically significant group differences were observed in bone mineral density (BMD) between the BF, MF, and SF groups, assessed using DXA or pQCT. At 6 y of age, children in the SF group showed significantly greater whole-body bone mineral content measured using DXA than those in the MF group. Six-month-old boys in the SF group demonstrated significantly greater levels of NTx than those in the MF group and significantly greater osteocalcin levels than those in the BF group. CONCLUSIONS: Together, these data suggest that although infants at age 6 mo in the SF group showed some enhanced bone metabolism compared with those in the BF and MF groups, as indicated by the urinary biomarkers, no differences in bone metabolism or BMD were noted between ages 2 and 6 y. This trial was registered at clinicaltrials.gov as NCT00616395.