Calcium borate

MineralCalciumBest with a meal

What is it

Calcium borate is a salt providing both calcium and boron. It is used as a fire retardant and wood preservative industrially, and occasionally as a source of boron in supplements.

Evidence for 1 use

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Bone and joint support

Limited Evidence

Small studies suggest boron may modestly support bone mineral metabolism and reduce calcium and magnesium loss; controlled clinical evidence is preliminary.

How it works

Boron is a trace element that plays a role in bone and joint health, possibly through effects on calcium, magnesium, and steroid hormone metabolism. It is found in plant foods. Calcium is essential for bones, muscle function, and nerve signaling. In calcium borate, the borate anion dissociates from calcium in the digestive tract and is absorbed. Boron, although not formally classified as essential for humans, is recognized as nutritionally important by some authorities, with typical intakes of 1-2 mg/day from food.

Dosage

There is no RDA for boron. A tentative upper limit is 20 mg/day for adults. Supplement products typically provide 1-3 mg of elemental boron per serving. The calcium fraction depends on product formulation.

When and how to take it

Take with food to reduce GI upset. Separate from thyroid medication and certain antibiotics by 4 hours due to calcium content.

1 commercial form

Compare the main delivery options and what they’re best suited for.

Calcium borate (supplement grade)

Used in some bone- and joint-focused formulas.

Provides both calcium and boron.

Safety

Boron at typical supplement doses (under 20 mg/day) is generally well tolerated. Higher doses can cause nausea, vomiting, headache, and rash. Industrial calcium borate is not intended for human consumption and is sold as a different product.

Who should be cautious

Avoid high-dose boron in pregnancy and breastfeeding; rodent studies suggest reproductive toxicity at very high doses. People with hormone-sensitive conditions should consult a clinician.

Interactions

Boron may modestly raise estrogen and testosterone levels in some studies, with theoretical relevance to people on hormone therapy. High calcium intake from any source can affect absorption of some antibiotics, thyroid medication, and iron.

Food sources

Avocado

Amount
1 fruit
%DV
—

Raisins

Amount
1/4 cup
%DV
—

Almonds

Amount
1 oz
%DV
—

Frequently asked questions

Is boron essential?⌄

Boron is not formally classified as essential for humans, though several health authorities recognize it as nutritionally important. Typical diets provide 1-2 mg per day.

How much boron is too much?⌄

The tentative upper limit is 20 mg per day for adults. Most supplements provide 1-3 mg per serving.

References

Calcium borate on Wikidata — Wikidata link

Calcium borate (PubChem CID 134660) — PubChem link

Calcium borate on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Calcium borate (PubMed search) — PubMed link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.