What it does in the body
Boron seems to be essential for healthy bone and joint function, possibly via effects on the balance and absorption of calcium, magnesium and phosphorus.¹ It seems to affect cell membranes and the way signals are transmitted across these membranes.
Boron affects the metabolism of steroid hormones and may also play a role in converting vitamin D to its more active form, thus increasing calcium uptake and deposition into bone. Boron also increases male sex hormone levels.

Absorption and metabolism
Boron is efficiently absorbed and excreted in the urine.

Deficiency
Boron deficiency seems to affect calcium and magnesium metabolism, and affects the composition, structure and strength of bone, leading to changes similar to those seen in osteoporosis.² This is likely to be due to decreased absorption and increased excretion of calcium and magnesium. Boron deficiency combined with magnesium deficiency appears especially damaging in cases of osteoporosis.³ Due to its effects on calcium and magnesium metabolism, boron deficiency may also contribute to the formation of kidney stones. Boron deficiency also seems to decrease mental alertness.⁴

There may also be a link between boron deficiency and osteoarthritis. Epidemiological studies indicate that in countries such as Mauritius and Jamaica, where boron intake is low, the incidence of osteoarthritis is around 50 to 70 percent. In countries such as the USA, UK and Australia, where boron intake is relatively high, the incidence of osteoarthritis is around 20 percent. Boron concentrations in bones next to osteoarthritic joints may be lower than in normal joints.⁵

Sources
Plant foods such as fruit, vegetables, soybeans and nuts are rich sources of boron but the level in food depends on the soil in which it is grown. The table below can be used as a guide. Wine, cider and beer also contain significant amounts of boron.⁶

Recommended dietary allowances
There is no RDA for boron. A safe and adequate daily intake is estimated to be between 1 and 10 mg.

Supplements
Sodium borate is the most common form of supplement. Boron is increasingly used in calcium and bone-replenishing nutritional formulas. It may be particularly useful in those whose magnesium intake is low. This effect may be useful in the prevention of kidney stones.⁷

Because of its effect on testosterone levels, boron supplements have been marketed to athletes on the basis of their ability to increase muscle mass and strength. A 1994 study of the effects on ten male bodybuilders did not find any increases in those with boron supplements.⁸

Toxic effects of excess intake
Toxic effects appear at intakes of about 100 mg. The World Health Organization has banned boron (in the form of boric acid) as a food additive and preservative. Toxic effects include a red rash with weeping skin, vomiting, diarrhea characterized by a blue green color, depressed blood circulation, coma and convulsions. A fatal dose in adults is 15 to 20 g and in children 3 to 6 g. Repeated intakes of small amounts can cause accumulative toxicity.

Therapeutic uses of supplements
Boron may be beneficial in the treatment of osteoporosis. Supplements of around 3 mg per day have been shown to enhance the effects of estrogen in postmenopausal women. This is likely to contribute to its beneficial effects on bone health.⁹

Studies done in 1994 on athletic college women suggest that boron supplements decrease blood phosphorus concentration and increase magnesium concentration. Both of these changes are beneficial to bone-building.¹⁰ Because of its sex hormone-enhancing effects, boron may help to protect against atherosclerosis.¹¹

Osteoarthritis
Boron supplements of 6 to 9 mg per day have been used to treat osteoarthritis with some improvement of symptoms. Boron content in arthritic bones may be lower than that of normal bones and extra boron may increase bone hardness.¹²

Other uses
Boron, in the form of boric acid, has been used as a dusting powder or lotion to treat bacterial and fungal infections. It is also a component of some commercial mouthwashes. In borax solution form, boron has been used to treat mouth ulcers, eye infections and as a nasal douche.

Interactions with other nutrients
Boron works with calcium, magnesium, phosphorus and vitamin D in bone metabolism, growth and development. Animal studies show that a deficiency of vitamin D increases the need for boron.

Cautions
The boric acid and borax forms of boron are toxic and should never be consumed. Boron-containing powders should not be applied to body cavities and mucous membranes as the body absorbs too much and toxic effects can occur.

1 McCoy H; Kenney MA; Montgomery C; Irwin A; Williams L; Orrell R. Relation of boron to the composition and mechanical properties of bone. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 49-53

2 Nielsen FH. Biochemical and physiologic consequences of boron deprivation in humans. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 59-63

3 Nielsen FH Studies on the relationship between boron and magnesium which possibly affects the formation and maintenance of bones. Magnes Trace Elem, 1990, 9:2, 61-9

4 Penland JG Dietary boron, brain function, and cognitive performance. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 65-72

5 Helliwell TR; Kelly SA; Walsh HP; Klenerman L; Haines J; Clark R; Roberts NB. Elemental analysis of femoral bone from patients with fractured neck of femur or osteoarthrosis. Bone, 1996 Feb, 18:2, 151-7

6 Hunt CD; Shuler TR; Mullen LM. Concentration of boron and other elements in human foods and personal-care products. J Am Diet Assoc, 1991 May, 91:5, 558-68

7 Hunt CD; Herbel JL; Nielsen FH 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. Am J Clin Nutr, 1997 Mar, 65:3, 803-13

8 Green NR; Ferrando AA Plasma boron and the effects of boron supplementation in males. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 73-7

9 Nielsen FH; Hunt CD; Mullen LM; Hunt JR. Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women. FASEB J, 1987 Nov, 1:5, 394-7

10 Meacham SL; Taper LJ; Volpe SL Effects of boron supplementation on bone mineral density and dietary, blood, and urinary calcium, phosphorus, magnesium, and boron in female athletes. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 79-82

11 Naghii MR; Samman S The effect of boron supplementation on its urinary excretion and selected cardiovascular risk factors in healthy male subjects. Biol Trace Elem Res, 1997 Mar, 56:3, 273-86

12 Newnham RE. Essentiality of boron for healthy bones and joints. Environ Health Perspect, 1994 Nov, 102 Suppl 7:, 83-5