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.
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