Curtiss D. Hunt

Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women.

A study was done to examine the effects of aluminum, magnesium, and boron on major mineral metabolism in postmenopausal women. This communication describes some of the effects of dietary boron on 12 women between the ages of 48 and 82 housed in a metabolic unit. A boron supplement of 3 mg/day markedly affected several indices of mineral metabolism of seven women consuming a low‐magnesium diet and five women consuming a diet adequate in magnesium; the women had consumed a conventional diet supplying about 0.25 mg boron/day for 119 days. Boron supplementation markedly reduced the urinary excretion of calcium and magnesium; the depression seemed more marked when dietary magnesium was low. Boron supplementation depressed the urinary excretion of phosphorus by the low‐magnesium, but not by the adequate‐magnesium, women. Boron supplementation markedly elevated the serum concentrations of 17β‐estradiol and testosterone; the elevation seemed more marked when dietary magnesium was low. Neither high dietary aluminum (1000 mg/day) nor an interaction between boron and aluminum affected the variables presented. The findings suggest that supplementation of a low‐boron diet with an amount of boron commonly found in diets high in fruits and vegetables induces changes in postmenopausal women consistent with the prevention of calcium loss and bone demineralization.— Nielsen, F. H.; Hunt, C. D.; Mullen, L. M.; Hunt, J. R. Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women. FASEB J. 1: 394‐397; 1987.

Dietary boron as a physiological regulator of the normal inflammatory response: A review and current research progress

A substantial number of metabolic processes in humans and animals are beneficially affected by physiologic amounts of dietary boron. There is emerging evidence that boron influences immune function. Specifically, there is evidence that dietary boron helps control the normal inflammatory process and may do so by serving as a signal suppressor that down-regulates specific enzymatic activities typically elevated during inflammation at the inflammation site. Suppression, but not elimination, of these enzyme activities by boron is hypothesized to reduce the incidence and severity of inflammatory disease. This is a review of previous findings describing an apparent positive effect of boron on aspects of physiology related to the inflammatory process, including joint swelling, restricted movement, fever, antibody production, hemostasis, serine protease and lipoxygenase activities, and leukotriene metabolism. It also summarizes current research findings on the immunomodulatory effects of physiologic amounts of dietary boron such as reduced paw swelling and circulating neutrophil concentrations and increased circulating concentrations of natural killer cells and CD8a+/CD4− cells of rats with antigen-induced arthritis. Possible biochemical mechanisms for the effects of boron on the induced inflammatory response are discussed, with emphasis on possible roles of boron in the respiratory burst mechanism, and inhibition of leukocyte 6-phosphogluconate dehydrogenase, gamma-glutamyl transpeptidase, cyclooxygenase, and serine proteases (elastase, chymase, cathepsin G, thrombin, and coagulation factors IXa, Xa, XIa) activities. J. Trace Elem. Exp. Med. 12:221–233, 1999. Published 1999 Wiley-Liss, Inc.

Dietary boron modified the effects of magnesium and molybdenum on mineral metabolism in the cholecalciferol-deficient chick

The metabolic effects of dietary boron, magnesium, and molybdenum on mineral metabolism in the cholecalciferol-deficient chick, with emphasis on growth cartilage histology, were studied. One-day-old cockerel chicks were assigned to groups in a fully-crossed, three factor, 2×2×2 design. The basal diet was based on ground corn, high-protein casein, and corn oil and contained 125 IU cholecalciferol (inadequate), 0.465 mg B, 2.500 mg Mg, and 0.420 mg Mo/kg. The treatments were the supplementation of the basal diet with B at O or 3; Mg at 300 (inadequate) or 500 (adequate); and Mo at 0 or 20 mg/kg.At d 25, B depressed mortality, alleviated the cholecalciferol-deficiency induced distortion of the marrow sprouts (MS) of the proximal tibial epiphysial plate, and elevated the numbers of osteoclasts within the MS.Adequate Mg exacerbated the cholecalciferol-deficiency induced bone lesions. Mo widened the MS markedly. In Mg-deficient chicks, B elevated plasma Ca and Mg concentrations and growth, but inhibited initiation of cartilage calcification; B had the opposite effect in Mg-adequate chicks. An interaction among B, Mg, and Mo affected plasma uric acid and glucose concentrations. B may function to modify mineral metabolism in cholecalciferol deficiency, suppressing bone anabolism in concurrent Mg deficiency and bone catabolism in concurrent Mg adequacy.

Learning and memory disabilities in young adult rats from mildly zinc deficient dams

Three experiments were conducted to test the behavior of the offspring of rat dams (ZD) fed a mildly zinc deficient diet (10.0 micrograms Zn/g) during pregnancy and lactation. Since zinc deficiency causes anorexia, a second group of rat dams (PF) was fed the same quantity of the diet during gestation and lactation as was consumed by their ZD mates. A third group of rats (AL) was fed the diet ad lib during gestation and lactation. The PF and AL dams were given zinc supplemented (25.0 micrograms Zn/ml) drinking water whereas the ZD dams were given double distilled, deionized drinking water. After weaning, the offspring of all dams were fed Purina Laboratory Chow ad lib until they were 100 days old. The offspring were then reduced to 85% of their ad lib weight and tested on a 17-arm radial maze for memory and learning. In Experiments 1 and 2, the ZD males suffered a significant learning deficit when compared to the AL males. Whereas the PF males suffered a significant learning impairment in Experiment 1, the learning deficit of the PF group was not as severe as the deficit of the ZD group. There was no impairment in reference (long-term) memory for any of the groups. In Experiment 3, significant differences in working (short-term) memory were found among the three groups of females. The ZD group was significantly inferior in working memory when compared to the PF and AL groups. No significant differences in working memory were found between the PF and AL groups.

Biochemical effects of physiological amounts of dietary boron

Research on human and animal boron nutrition has progressed sufficiently over the past decade to develop working hypotheses for biochemical roles of the element. It is well established that vascular plants, diatoms, and some species of marine algal flagellates have acquired an absolute requirement for boron although the primary role remains unknown. Discovery of naturally-occurring boron oxy compounds, all ionophoric macrodiolide antibiotics with a single boron atom critical for activity, established at least one biochemical role of boron. Recent findings suggest that physiological amounts of supplemental dietary boron (PSB) affect a wide range of metabolic parameters in chick and rat model systems as well as humans. Cholecalciferol (vitamin D3) regulates energy substrate utilization; current findings indicate that boron modifies that regulatory function. For example, in chicks, PSB substantially corrected vitamin D3-deficiency-induced elevations in plasma glucose concentrations. Boron also alleviates perturbations in mineral metabolism characteristic of vitamin D3 deficiency. In rachitic chicks, PSB alleviated distortion of the marrow sprouts in the proximal tibial epiphysial plate. Boron may help prevent inflammatory disease as several key regulatory enzymes in the inflammatory response are inhibited by PSB. The findings to date support the hypothesis that boron is essential for animals and humans. Also, boron and vitamin D3 have the same overall effect on the utilization of energy substrates found in plasma. Further advances in boron nutrition research will probably include characterization of the mechanisms through which boron modulates immune function, insulin release, and vitamin D metabolism.

Aluminum, Boron, Calcium, Copper, Iron, Magnesium, Manganese, Molybdenum, Phosphorus, Potassium, Sodium, and Zinc: Concentrations in Common Western Foods and Estimated Daily Intakes by Infants; Toddlers; and Male and Female Adolescents, Adults, and Seniors in the United States

Intakes of 12 minerals by various population groups within the USA were estimated, to allow calculation of molar to molar elemental ratios in individual foods and total diet, and to facilitate evaluation of mineral pairs with demonstrated competitive metabolism (e.g. Ca and Fe). Age groups examined were infants (6–11 months), toddlers (2 yr), adolescents (14–16 yr), adults (25–30 yr) and elderly subjects (60–65 yr); adolescent, adult and elderly groups were further subdivided into males and females, giving a total of 8 age-sex groups. 234 foods taken as representative of the average US diet were analysed for the 12 minerals and estimates of daily intake of each analysed food were made for each age-sex group, based on the Total Diet Study model. For all groups, grain products accounted for >50% of total daily Al intake. Infant foods supplied 47% of B intake, whereas for toddlers, B intake from fruit and fruit juices was twice than from milk/cheese. For adolescents, milk/cheese foods were the single most important source of B, whereas for adults/elderly, the most significant source was beverages (largely instant coffee). Milk/cheese products supplied most Ca for all groups (44–70%). For all groups except infants, meat/poultry/fish was the most important source of Cu (19–43%), whilst for infants, infant foods were the main source (48%). Grain products provided most dietary Fe (34–46%) for all groups except infants, who relied upon infant foods for Fe. Milk/cheese foods contributed heavily to Mg intakes of infants (34%), toddlers (25%) and adolescents (20–22%), whereas beverages contributed most Mg to diets of adults and elderly (17–21%). Apart from infants, all groups received most Mn from grain products (29–45%). Milk/cheese supplied most Mb to infants, toddlers and adolescents (27–40%), as well as most P (32–48%). Adults and elderly subjects gained most P from meat/poultry/fish. Milk/cheese provided most K for infants, toddlers and adolescents (28–42%), whereas meat/poultry/fish served this role for adults and elderly subjects. The primary source of Na for infants was milk/cheese and for all other groups, except adult males, the primary Na source was grain products. The primary source of Zn was meat/poultry/fish for all groups except infants.

Assessing the effects of low boron diets on embryonic and fetal development in rodents using in vitro and in vivo model systems

To date, boron (B) essentiality has not been conclusively shown in mammals. This article summarizes the results of a series of in vitro and in vivo experiments designed to investigate the role of B in mammalian reproduction. In the first study, rat dams were fed either a low (0.04 μg B/g) or an adequate (2.00 μg B/g) B diet for 6 wk before breeding and through pregnancy; reproductive outcome was monitored on gestation day 20. Although low dietary B significantly lowered maternal blood, liver, and bone B concentrations, it had no marked effects on fetal growth or development. The goal of the second study was to assess the effects of B on the in vitro development of rat postimplantation embryos. Day 10 embryos collected from dams fed either the low or adequate B diets for at least 12 wk were cultured in serum collected from male rats exposed to one of the two dietary B treatments. Dams fed the low B diet had a significantly reduced number of implantation sites compared to dams fed the B-adequate diet. However, embryonic growth in vitro was not affected by B treatment. The aim of study 3 was to define the limits of boric acid (BA) toxicity on mouse preimplantation development in vitro. Two-cell mouse embryos were cultured in media containing graded levels of BA (from 6 to 10,000 μM). Impaired embryonic differentiation and proliferation were observed only when embryos were exposed to high levels of BA (>2000 μM), reflecting a very low level of toxicity of BA on early mouse embryonic development. Study 4 tested the effects of low (0.04 μg B/g) and adequate (2.00 μg B/g) dietary B on the in vitro development of mouse preimplantation embryos. Two-cell embryos obtained from the dams were cultured in vitro for 72 h. Maternal exposure to the low B diet for 10, 12, and 16 wk was associated with a reduction in blastocyst formation, a reduction in blastocyst cell number, and an increased number of degenerates. Collectively, these studies support the concept that B deficiency impairs early embryonic development in rodents.

Dietary boron enhances efficacy of cholecalciferol in broiler chicks

Accumulating evidence suggests that boron influences the metabolism of cholecalciferol in humans and animals. This study was designed to characterize further the relation between boron and cholecalciferol. Two 2 X 3 factorially designed experiments were conducted with boron (0 and 3 mg/kg) and cholecalciferol [0, 3.13 (Expt 1) or 5.0 (Expt 2), and 15.63 μg/kg] supplemented to a low-boron (<0.18 mg/kg), noncholecalciferol-added basal diet. Each diet was fed to 16 broiler chicks divided in two groups, housed in plastic cages, from 1 d to either 27 d (Expt 1) or 26 d (Expt 2) of age. In Expt 1, chicks fed the basal diet, compared to those fed supplemental cholecalciferol, exhibited rickets and increased bone concentrations of sodium, potassium, zinc, copper, and manganese, and reduced bone dry weights and concentrations of iron. Supplemental boron improved growth, feed efficiency, and gait abnormalities and increased concentrations of serum 25-hydroxycholecalciferol, ionized calcium and triglycerides, and bone iron, and reduced concentrations of bone sodium, potassium, zinc, and copper in chicks fed 3.13, but not 0 and 15.63, μg cholecalciferol/kg diet. Supplemental boron increased bone boron concentrations regardless of cholecalciferol status. In Expt 2, the effects of boron on these variables were similar but less pronounced. These findings suggest that boron enhances the efficacy of cholecalciferol, but boron does not substitute for the vitamin. Further study is needed to determine whether boron enhances cholecalciferol absorption or hydroxylation.

Dietary boron intakes of selected populations in the United States

Knowledge of daily boron (B) intakes will assist researchers in establishing B requirements and elucidating the metabolic role of B in humans. B concentrations in commonly consumed foods were utilized to approximate the B intake of selected US populations. Triplicate food samples were digested at low temperatures with 16M HNO3 and 30% H2O2, and analyzed by inductively coupled plasma spectroscopy (ICP). Milk and dairy products, juices, and beverages were the largest contributors to dietary B. Total B content of average daily diets ranged from 548 μg for toddlers (2 yr old) to 883 μg for mature males (60–65 yr old), excluding tap water contributions. Toddlers consumed 3.7 times more B than mature males when adjusted for body weight (body wt) and consumed the diet with the highest boron density (1.8 μg/kJ or 0.43 μg/kcal). Adolescent females consumed a diet with the lowest B density (1.12 μg/kJ or 0.26 μg/kcal). Food B concentrations applied to diet records (1020 μg/d) and ICP analysis of the corresponding food composites (1170 μg/d) were comparable (p < 0.05). Current estimations of B in US diets are consistent with reports in the literature stating that normal adult daily B intakes are approx 1 mg.

Transmembrane partitioning of boron and other elements in RAW 264.7 and HL60 cell cultures

The trace element boron is essential for all higher plants and is beneficial or has been established as essential for several animal models of human nutrition. To help identify the biomolecules that require boron for function in humans, we determined whether intracellular boron is retained against a concentration gradient. Cells (Abelson leukemia virus BALB murine monocyte-macrophage RAW 264.7 [RAW] and HL60) and supplemented media (Dulbecco’s modified essential media [+10% fetal calf serum] and Iscove’s modified Dulbecco’s medium [+5% fetal calf serum], respectively) were analyzed for mineral concentrations after culture and subculture. Special corrections were made for trapped extracellular media in cell pellets and endocytosed media. For RAW cells, the partitioning coefficients (PC; intracellular/extracellular ratios) were, in rank order, as follows: Mn, 110; Fe, 67; P, 65; Zn, 32; K, 15; Cu, 7.1; Mg, 4.3; B, 1.7; Ca, 0.4; Na, 0.3. For HL60 cells, the partitioning coefficients were, in rank order, as follows: Mn, 212; Zn, 211; P, 123; K, 21; Fe, 16; Mg, 11; B, 1.7; Ca, 0.8; Na, 0.3. Trapped extracellular media was estimated to be 6.7±0.8%; trapped extracellular and endocytosed media together was 24.8±0.3% of the mass within the isolated cell pellets. The partitioning coefficients indicate a positive gradient for intracellular accumulation of boron, zinc, phosphorus, managanese, magnesium, potassium, iron, and copper in RAW264.7 and HL60 cells. Specifically, the data indicate the existence of a selective boron-binding molecular species within the cell or the existence of a boron-specific membrane transporter.