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The tolerable upper intake level (UL), or upper limit, for boron is 20 mg a day for adults 19 and older. That is the most a day that is unlikely to cause harm for almost everyone; above it, the chance of side effects goes up. It is a ceiling, not a target. The limit counts boron from food, water and supplements together.
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Servings a day
This limit is the same for adults 19 and older, including pregnancy and breastfeeding.
Type the amount from your label to compare it with the upper limit.
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Boron upper limits by age
| Age | Males | Females | Pregnancy | Breastfeeding |
|---|---|---|---|---|
| Birth to 6 months | Not set | Not set | – | – |
| 7-12 months | Not set | Not set | – | – |
| 1-3 years | 3 mg | 3 mg | – | – |
| 4-8 years | 6 mg | 6 mg | – | – |
| 9-13 years | 11 mg | 11 mg | – | – |
| 14-18 years | 17 mg | 17 mg | 17 mg | 17 mg |
| 19-30 years | 20 mg | 20 mg | 20 mg | 20 mg |
| 31-50 years | 20 mg | 20 mg | 20 mg | 20 mg |
| 51-70 years | 20 mg | 20 mg | – | – |
| 71+ years | 20 mg | 20 mg | – | – |
No upper limit could be set for babies; the National Academies say their intake should come from food and formula only.
How much Boron you need
No RDA or Adequate Intake has been set for boron: the National Academies found too little data to say how much people need.
What counts toward the Boron limit
The limit counts boron from food, water and supplements together.
What happens with too much Boron
The National Academies based the adult UL of 20 mg a day on animal data, because no human data on reproduction were available: the report says "reproductive and developmental effects were selected as the critical endpoint," using a study in which pregnant rats were fed boric acid (Price and coworkers, 1996) and the most sensitive sign was lower fetal weight, with a no-observed-adverse-effect level of 9.6 mg per kg of body weight a day divided by an uncertainty factor of 30. The report found no data on harm from large amounts of boron in food and water; in case reports of boric acid and borax poisoning, "initial symptoms include nausea, gastric discomfort, vomiting, and diarrhea," with skin flushing, excitation, convulsions, depression and vascular collapse reported at higher doses. It adds that animal studies, though not human data, showed high doses of borax or boric acid harming the testis and male fertility, and that people given borates to treat epilepsy developed dermatitis, hair loss, loss of appetite and indigestion.
Sources: National Academies, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001); Health Canada, Dietary Reference Intakes tables (the joint U.S.-Canada values). Limits checked November 8, 2026. More from the NIH: Office of Dietary Supplements Boron fact sheet.
If you think you or a child took too much of a supplement, call Poison Control at 1-800-222-1222 (U.S., free, 24 hours) or use poison.org. In an emergency, call 911.
General information, not medical advice. Your doctor may recommend a different amount, for example to treat a deficiency. Talk to your doctor or pharmacist before you start, stop or change a supplement, especially if you are pregnant, nursing, take medication or have a medical condition.