Boron

  • Boron has long been known to be essential for plant growth and development but its role remains elusive. Several roles have been postulated for boron in plant cells: cell wall synthesis, lignification and structure; nucleic acid synthesis and metabolism; carbohydrate, indole acetic acid and phenol metabolism (1). Since boron can form diester bridges between cis-hydroxyl-containing molecules it has been recently suggested that boron could serve to stabilize molecules with cis-diol groups, in plants at least and that would turn them effective, irrespectively of their biological function (2).
  • It occurs in the human body in trace amounts. Its role in human nutrition is still sketchy and there is no clear evidence that boron is an essential element.
  • As demonstrated in animal models there is evidence to suggest that boron supplementation at a physiological level affects a wide range of metabolic parameters. Thus, it was found that boron stimulates growth in cholecalciferol-deficient chicks but not in the birds receiving adequate amounts of vitamin D3. This suggests boron may influence some aspect of vitamin D3 metabolism or is synergistic with vitamin D3 with respect to bone growth (3). In rats it was found that supplemental dietary boron has most marked effects when the diet is deficient in known nutrients. There was also a higher intake versus excretion ratio for calcium, magnesium and phosphorus in rats fed a vitamin D deficient diet supplemented with boron as compared to control animals (4).
  • In mammals the boron transporter NaBCl functions as electrogenic sodium-coupled borate transporter. This transporter is essential for cell growth and proliferation (5).
  • Boron supplementation to broiler chicks affected plasma levels of iron, copper, zinc and bone (tibia) concentration of boron, zinc and calcium. In addition, blood hematocrit and hemoglobin counts increased by boron supplementation (6). These results would suggest that boron may play an important role in mineral metabolism through biochemical and hematological mechanisms.
  • In rodents (rats) a low boron diet was shown to impair early embryonic development (7).
  • Health benefits: Boron supplementation may reduce body calcium loss by increasing the beneficial effects of estrogen on bone health. Thus, boron supplementation with amounts commonly found in diets high in fruits and vegetables to postmenopausal women markedly decreased the urinary excretion of calcium and magnesium, particularly when the magnesium intake was low (8). In the same time there was a marked increase of serum 17 b-estradiol and testosterone. In another study on postmenopausal women it was found that changing boron intake from low (0.33 mg/day) to high (3.33 mg/day) had no effect on mineral and steroid metabolism as shown by the bone mineral absorption and excretion and plasma steroid hormone levels. However, the low boron diet appeared to induce hyperabsorption of calcium since positive calcium balance were recorded in combination with elevated urinary calcium excretion (9). In healthy men it was found that boron suplementation (10 mg/day for 4 weeks) resulted in elevated plasma estradiol concentration but there was no difference in LDL susceptibility to oxidation between the control and the supplemented group and based on these findings it was suggested that boron may be involved in protection against atherosclerosis (10).
  • Best food sources: fresh fruits and vegetables.


References
1. Blevins, D.L. & Lukaszewski, K.M. (1994) Environ. Health Perspect. 102(Suppl.7) 31-33. Proposed physiologic functions of
    boron in plants pertinent to animal and human metabolism.
2. Bolanos, L. et al. (2004) Plant Physiol.Biochem. 42(11) 907-912. Why boron?
3. Hunt, C.D. (1994) Environ. Health Perspect. 102(Suppl.7) 35-43. The biochemical effects of physiologic amounts of dietary
    boron in animal nutrition models.
4. Dupre, J.N. et al. (1994) Environ. Health Perspect. 102(Suppl.7) 55-58. Effects of dietary boron in rats fed a vitamin D3-
    deficient diet.
5. Park, M. et al. (2005) Cell Cycle 4(1) 24-26. Borate transport and cell growth and proliferation.
6. Kurtoglu, F. et al. (2005) Br.Poult.Sci. 46(1) 87-96. Effects of dietary boron supplementation on some biochemical
    parameters, peripheral blood lymphocytes, splenic plasma cells and bone characteristics of broiler chicks given diets with adequate or inadequate cholecalciferol (vitamin D3) content.
7. Lanoue, L. et al. (1998) Biol. Trace Elem.Res. 66(1) 271-298. Assessing the effects of low boron diets on embryonic and
    fetal development in rodents using in vitro and in vivo model systems.
8. Nielsen, F.H. et al. (1987) FASEB J. 1(5) 394-397. Effect of dietary boron on mineral, estrogen and testosterone metabolism
    in postmenopausal women.
9. Beattie, J.H. & Peace, H.S. (1993) Br.J.Nutr. 69(3) 871-884. The influence of a low-boron diet and boron supplementation
    on bone, major mineral and sex steroid metabolism in postmenopausal women.
10. Naghii, M.R. & Samman, S. (1997) Biol. Trace Elem.Res. 56(3) 273-286. The effect of boron supplementation on its
    urinary excretion and selected cardiovascular risk factors in healthy male subjects.