Breast milk stimulates growth hormone secretion in infant mice, and phosphorus insufficiency disables this ability and causes dwarfism-like symptoms

INTRODUCTION: Breast milk intake facilitates neonatal growth, and its effect is assumed to last long into the adulthood. We recently reported that dietary phosphorus insufficiency reduces the ability of breast milk to promote infant growth in mice. However, how phosphorus confers this ability to milk is still unclear. METHODS: To address this issue, we performed biochemical and physiological comparisons of milk secreted from C57BL/6J mice fed a low-phosphorus diet (LPD) or a normal-phosphorus control diet. RESULTS: Although serum phosphorus concentration was decreased, the body weight of mother mice was unaffected. By contrast, infant body weight was significantly reduced, and dwarfism-like symptoms were observed in adulthood. Quantitative analysis revealed that the serum concentration of growth hormone (GH) was substantially reduced, and concomitantly insulin-like growth factor 1 and fibroblast growth factor 23 were decreased. Immunohistochemical analysis revealed ectopic fat accumulation in the livers of infant mice along with increased blood cholesterol level. Moreover, electron microscopy indicated fragility of the outer membrane of milk droplets. CONCLUSIONS: Our results suggest that phosphorus is essential for the formation of milk droplets, which function as a stimulator of growth factor secretion in infant offspring.