METABOLIC RESPONSES OF POSTMENOPAUSAL WOMEN TO SUPPLEMENTAL DIETARY BORON AND ALUMINUM DURING USUAL AND LOW MAGNESIUM INTAKE - BORON, CALCIUM, AND MAGNESIUM ABSORPTION AND RETENTION AND BLOOD MINERAL CONCENTRATIONS

Findings from animal studies indicate that dietary boron affects sever al aspects of mineral metabolism, especially when animals are subjecte d to nutritional stressors. Eleven postmenopausal volunteers living on a metabolic ward for 167 d (one 23-d equilibration period and six 24- d treatment periods) were fed a conventional basal diet that supplied a daily average intake of 0.36 mg B, 109 mg Mg, and < 0.10 mg Al/8400 kJ. They were given supplements of 0 (BE) or 3 mg B (SE, last two peri ods only), 0 (BMg) or 200 mg Mg (SMg) (with magnesium supplements held constant during the last two periods), or 0 (BAl) or 1000 mg Al (SAl) /d. The SE treatment, compared with the BE treatment, provided a 9.0-f old increase in dietary boron but yielded only a 1.5-fold increase in plasma boron concentrations. Regardless of boron dietary treatment, fe cal plus urinary excretion of boron accounted for nearly 100% of dieta ry boron intake with no evidence of boron accumulation over time. Lack of boron accumulation and relatively small changes in blood boron val ues during a substantial increase in dietary boron support the concept of boron homeostasis. In subjects fed BMg, SE decreased the percentag e of dietary calcium lost in the urine but increased that percentage i n volunteers fed SMg, a relation that may be important in understandin g metabolic mineral disorders that perturb calcium balance. Reduced ca lcium absorption during SAI suggests that aluminum supplementation sho uld be limited or at least monitored in postmenopausal women prone to excessive calcium loss. Decreased total urinary oxalate during SE in B Mg subjects indicates a possible role for boron in the control of urol ithiasis during low-magnesium nutriture.