Boron concentrations in milk from mothers of full-term and premature infants.

BACKGROUND Boron is a bioactive element that satisfies several of the criteria for essentiality in humans. OBJECTIVE The objective was to establish the profile of boron metabolism in human milk. DESIGN Lactating mothers of premature (PRT; n = 10, <2000 g birth weight, <37 wk gestation) and full-term (FT; n = 10, >2500 g, 39-41 wk gestation) infants living in St John's, Canada, collected milk samples once a week for 12 wk. Samples were analyzed for boron, copper, iron, selenium, and zinc by atomic emission or absorption spectrometry after wet-ash digestion with nitric acid and hydrogen peroxide in polytetrafluoroethylene tubes. RESULTS A mixed-model analysis of variance indicated that boron concentrations were stable in full-term (30 and 28 mug/L milk; P = 0.5) but not in preterm (37 and 27 mug/L; P = 0.01) milk between weeks 1 and 12, respectively. As expected, there were reductions in the concentrations of copper (FT: 651 to 360 mug/L, P < 0.0001; PRT: 542 to 425, P = 0.05), iron (FT: 355 to 225 mug/L, P = 0.0003; PRT: 406 to 287, P = 0.002), selenium (FT: 26.9 to 18.6 mug/L, P < 0.0001; PRT: 28.7 to 20.4, P < 0.0001), and zinc (FT: 4060 to 1190 mug/L, P < 0.0001; PRT: 5970 to 1270, P < 0.0001) over time. CONCLUSIONS The stable milk boron concentrations over time suggest that boron may be under homeostatic control. The patterns of change in copper, iron, selenium, and zinc concentrations in milk differ from those of boron. Further research is needed to elucidate the mechanism of milk boron secretion.