Study: Soy-based infant formula may improve bone metabolism in early life

Key takeaways:

• Infants fed soy-based formulas had better bone metabolism at 6 months than those fed breast milk or dairy-based formula.
• There were no differences in bone metabolism or bone mineral density at older ages.

Urinary markers indicated that infants who were fed soy-based formulas had better bone metabolism at 6 months than those fed breast milk or dairy-based infant formula, according to research in the American Journal of Clinical Nutrition.

However, “these effects were transient and absent at 2 years, when [soy formula] was no longer being fed,” researchers wrote.

How infants are fed can affect their skeletal development, Jin-Ran Chen, MD, PhD, MS, an associate professor of pediatrics and researcher at the University of Arkansas for Medical Sciences, and colleagues wrote. During the first year of life, most are fed breast milk, dairy-based infant formula or soy-based infant formula.

About 12% of infants in the United States consume soy-based infant formula, according to the National Health and Nutrition Examination Survey 2003–2010. The American Academy of Pediatrics currently recommends breastfeeding for infants and dairy-based infant formula as a second choice when breastfeeding is not possible.

Soy-based infant formula, on the other hand, “is only recommended for infants with galactosemia or congenital lactase deficiency,” Chen and colleagues wrote. Despite worries of how soy-associated isoflavones affect bone metabolism and structure, there are few studies that have investigated these connections.

“Numerous studies have shown benefits of breastfeeding for overall growth in term or pre-term infants, but there are limited data for how mode of postnatal feeding impacts short- and longer-term bone health,” they wrote. “In this regard, dairy based infant formula and soy-based infant formula may be beneficial for bone growth due to their content of specific factors, i.e., minerals, phytonutrients, and phytochemicals, for bone development.”

So, Chen and colleagues conducted a longitudinal observational study to evaluate the early impacts that soy-based infant formula might have on bone metabolism and structure compared with dairy-based infant formula and breast milk.

The researchers followed 433 healthy infants from 3 months to 6 years of age. They used dual-energy X-ray absorptiometry and peripheral quantitative computed tomography to assess the children’s skeletal development and immunoassays at specific intervals — 6 months, 24 months, 60 months and 72 months — to evaluate urinary biomarkers of bone metabolism.

Chen and colleagues found that infants fed soy-based formulas had better bone metabolism at 6 months than those fed breast milk or dairy-based infant formula. However, there were no differences in bone metabolism or bone mineral density between children aged 2 years to 6 years.

At age 6, the researchers noted that kids who were fed soy-based formulas as infants had significantly better bone mineral content, compared with those who were fed dairy-based infant formula.

Also, 6-month-old boys who were fed soy-based formula had much higher levels of N-terminal telopeptide of type I collagen (NTx) compared with boys who were fed dairy-based infant formula. The boys fed soy-based formula also saw significantly greater osteocalcin levels compared to boys who were fed breast milk. There were no significant differences in these markers among girls.

“Osteocalcin is released by mature osteoblasts during bone remodeling and NTx is released as a product of bone resorption. Thus, soy-based infant formula males had greater bone remodeling in the first 6 months of life compared to other feeding groups,” they wrote. “This may be due in part to the fact that soy-based infant formula infants had lower bone mineral content at 3 months of age compared to dairy-based infant formula and breastfeeding, prompting greater remodeling during the first 6 months of life.”

However, Chen and colleagues wrote that “additional studies are needed to determine if the significant differences observed are clinically relevant, as there were no other significant differences in urinary markers collected at any other time point in the study.” Further studies may also “help to elucidate the clinical relevance of the sex-specific differences observed in our study,” they wrote.