Boron: Benefits, Dosage, and Safety

What boron is

Boron is a trace element naturally present in many foods, especially plant foods, and available as a dietary supplement. It occurs in foods and beverages as inorganic borates and as sugar-borate esters such as calcium fructoborate. Most ingested boron is hydrolyzed to boric acid in the gastrointestinal tract, and the body absorbs about 85 to 90 percent of it. According to the NIH Office of Dietary Supplements, boron is not classified as an essential nutrient for humans because research has not yet identified a clear biological function for it.

What it does

• Boron is not an essential nutrient and has no confirmed required biological function in humans, per ODS
• May have beneficial effects on calcium metabolism and bone formation (proposed, not established)
• May influence the function of steroid hormones, including vitamin D and estrogen (proposed)
• May play a role in brain function and mental alertness (limited evidence)
• May affect insulin and energy substrate metabolism and immunity (proposed)
• Is a structural component of plant cell walls and required for plant growth (its established role is in plants, not humans)

Intake and dosing

Boron is not an essential nutrient, so no Recommended Dietary Allowance or Tolerable Upper Intake Level has been set. Doses in studies vary widely. Because supplement doses are not standardised, discuss an appropriate amount with a clinician or pharmacist.

Deficiency and who is at risk

Boron deficiency signs and symptoms have not been firmly established in humans. Limited data suggest a low-boron diet might reduce mental alertness and impair executive brain function. Low intakes (about 0.23 to 0.25 mg boron per 2,000 kcal) have been associated with increased urinary calcium and magnesium excretion, lower serum estrogen in postmenopausal women, and reduced plasma calcium and serum 25-hydroxyvitamin D with raised calcitonin and osteocalcin in men and women, changes that could theoretically affect bone. These are limited, not established, findings.

Who may need more

• No group has an established need for boron supplementation because boron is not classified as an essential nutrient and has no RDA or AI
• Median US dietary intakes (about 0.87 to 1.35 mg/day in adults) are well within the WHO acceptable safe range of 1 to 13 mg/day, and boron deficiency is not a recognized clinical condition
• Vegetarians tend to have higher boron intakes because boron is plentiful in plant foods
• People taking boron supplements for osteoarthritis or bone health should note that evidence remains preliminary and unconfirmed

Food sources

Plant foods provide the most boron: fruit, tubers, and legumes. Top per-serving sources include prune juice (1.43 mg/cup), raw avocado (1.07 mg/half cup), raisins (0.95 mg/1.5 oz), peaches (0.80 mg each), grape juice (0.76 mg/cup), apples (0.66 mg each), pears (0.50 mg each), roasted peanuts (0.48 mg/oz), and refried beans (0.48 mg/half cup). In US diets the main contributors are coffee, milk, apples, dried and cooked beans, and potatoes because of the amounts consumed. Wine, cider, and beer also contain boron. USDA FoodData Central does not list the boron content of foods, so data are limited.

Forms and absorption

Supplements contain elemental boron typically in the range of 0.15 to 6 mg. Common forms include sodium borate, sodium tetraborate, boron amino acid chelate, boron ascorbate, boron aspartate, boron citrate, boron gluconate, boron glycinate, boron picolinate, and calcium fructoborate. In a small human study, boron as sodium tetraborate significantly raised plasma boron within 4 to 6 hours, but no data are available on the relative bioavailability of the different supplemental forms. Supplement Facts labels declare the amount of elemental boron, not the weight of the whole compound.

Safety, excess and interactions

Too much

No data are available on adverse effects of high boron intakes from food or water. Accidental consumption of boric acid or borax (found in some cleaning products and pesticides) has caused nausea, gastrointestinal discomfort, vomiting, diarrhea, skin flushing, rash, excitation, convulsions, depression, and vascular collapse. Reported toxic amounts ranged from 18 to 9,713 mg, mostly in children under 6 years. Boron toxicity can also cause headache, hypothermia, restlessness, weariness, renal injury, dermatitis, alopecia, anorexia, and indigestion. In infants, high intakes have caused anemia, seizures, erythema, and thin hair. Extremely high doses (about 15,000 to 20,000 mg) can be fatal in adults. The FNB set the ULs based on reproductive and developmental effects observed in animals.

Interactions to know

• Boron is not known to have any clinically relevant interactions with medications, according to the NIH Office of Dietary Supplements

How status is measured

Not routinely measured in clinical practice. Most studies suggest urinary boron levels correlate with intake. Boric acid is the main form measured in blood, urine, and other body fluids; fasting plasma boron in postmenopausal women ranges from 34 to 95 ng/mL (3.14 to 8.79 micromol/L).

Regulated as a dietary supplement ingredient under DSHEA, not as a drug; supplements are not FDA-approved to diagnose, treat, cure, or prevent disease. Because the FNB has not established an RDA or AI for boron, the FDA has not set a Daily Value (DV), and boron does not appear with a percent DV on Supplement Facts labels.

What the evidence supports

We grade the strength of evidence behind each common reason people take boron, mirroring how the NIH describes it.