Adgent MA, et al. - Researchers performed a comparison of estrogen-responsive postnatal development in infants exclusively fed soy formula, cow-milk formula, and breast milk. In this study, girls fed soy formula demonstrated tissue- and organ-level developmental trajectories consistent with response to exogenous estrogen exposure compared to those fed cow-milk formula relative to those fed cow-milk formula.

Methods

• Four hundred and ten infants born in Philadelphia-area hospitals between 2010 and 2014 were enrolled.
• Throughout the study (birth to 28 or 36 weeks for boys and girls, respectively), 283 of the enrolled infants were exclusively fed soy formula (n = 102), cow-milk formula (n = 111), or breast milk (n = 70).
• Researchers performed repeated measurement of maturation index (MI) in vaginal and urethral epithelial cells using standard cytological methods, uterine volume and breast-bud diameter using ultrasound, and serum estradiol and follicle-stimulating hormone levels.
• Using mixed-effects regression splines, MI, organ-growth, and hormone trajectories were estimated by diet.

Results

• Cow-milk–fed and soy-fed infants did not differed regarding maternal demographics, however, these differed between formula-fed and breastfed infants.
• In soy-fed girls vs cow-milk–fed girls, vaginal-cell MI trended higher (P = 0.01) and uterine volume decreased more slowly (P = 0.01); however, no differences regarding their trajectories of breast-bud diameter and hormone concentrations were observed.
• Boys fed cow-milk vs soy formula showed no significant differences; estradiol was not detectable.
• Breastfed infants and soy-formula–fed infants differed in terms of vaginal-cell MI, uterine volume, and girls’ estradiol and boys’ breast-bud diameter trajectories.