Isoflavone exposure throughout suckling results in improved adult bone health in mice.

Exposure to isoflavones (ISO), abundant in soy protein infant formula, for the first 5 days of life results in higher bone mineral density (BMD), greater trabecular connectivity and higher peak load of lumbar vertebrae (LV) at adulthood. The effect of lengthening the duration of exposure to ISO on bone development has not been studied. This study determined if providing ISO for the first 21 days of life, which more closely mimics the duration that infants are fed soy protein formula, results in higher BMD, improved bone structure and greater strength in femurs and LV than a 5-day protocol. Female CD-1 mice were randomized to subcutaneous injections of ISO (7 mg/kg body weight/day) or corn oil from postnatal day 1 to 21. BMD, structure and strength were measured at the femur and LV at 4 months of age, representing young adulthood. At the LV, exposure to ISO resulted in higher (P < 0.05) BMD, trabecular connectivity and peak load compared with control (CON). Exposure to ISO also resulted in higher (P < 0.05) whole femur BMD, higher (P < 0.05) bone volume/total volume and lower (P < 0.05) trabecular separation at the femur neck, as well as greater (P < 0.05) peak load at femur midpoint and femur neck compared with the CON group. Exposure to ISO throughout suckling has favorable effects on LV outcomes, and, unlike previous studies using 5-day exposure to ISO, femur outcomes are also improved. Duration of exposure should be considered when using the CD-1 mouse to model the effect of early life exposure of infants to ISO.