Boron

What it is

Boron is a metalloid that occurs in food mainly as boric acid and borate. Good sources according to the NIH are prune juice with 1.43 mg per cup, avocado, raisins, peaches and grape juice. Adults in the US take in a median of 0.87 to 1.35 mg per day from food. In Germany, boron intake was not recorded in the large national consumption survey, but a boron-rich diet and certain mineral waters can increase it considerably.

There is no intake recommendation from either EFSA or the D-A-CH societies, because no specific function of boron in humans has yet been identified. The WHO gives an acceptable range of 1 to 13 mg per day. In supplements, boron is found for example as boric acid, sodium borate, glycinate or as calcium fructoborate, a compound of boron, calcium and fructose.

How it is supposed to work

Boron is said to intervene in the metabolism of calcium, magnesium, vitamin D and steroid hormones. The promises are derived from this: stronger bones, less joint inflammation, more free testosterone through less binding to the transport protein SHBG.

For part of this there are human data. In a metabolic ward, 12 postmenopausal women first received a low-boron diet for 119 days and then 3 mg boron per day. Urinary excretion of calcium and magnesium fell markedly, and estradiol and testosterone in the blood rose. A British research group repeated the experiment with a similar design over 3 weeks and found no change in minerals, hormones or bone resorption markers.

In men, the best-known positive finding comes from a study with 8 participants. After one week with 10 mg boron daily, free testosterone had risen and estradiol had fallen, and inflammatory markers were lower. There was no placebo group over that week.

What the studies show

Women in the metabolic ward

Twelve women aged 48 to 82 lived for months in a metabolic ward, first with about 0.25 mg boron per day, then with an additional 3 mg. On boron, the loss of calcium and magnesium in the urine fell, and estradiol and testosterone rose, especially with low magnesium intake. This is the much-cited testosterone study, but it examined women after boron deprivation, not men.

Bodybuilders: no effect

Nineteen young bodybuilders received 2.5 mg boron or placebo for 7 weeks. Both groups gained in testosterone, muscle mass and strength, so the training worked. Boron made no difference. To this day it is the only randomized, placebo-controlled study on boron and testosterone in men that we have found.

Knee discomfort, two weeks

Sixty people with knee discomfort took calcium fructoborate or placebo for 14 days. In both pain questionnaires, the boron group improved more, markedly so after 14 days. A second short study with 60 osteoarthritis patients found lower inflammatory markers over 15 days. Longer studies are missing.

One year in young women

In a study with 17 female athletes and 11 inactive female students, the participants received boron or placebo for one year. Boron changed individual blood values such as phosphorus and magnesium. Bone mineral density depended mainly on exercise: it rose slightly in the athletes and fell in the inactive women.

Where the data stop

As a testosterone booster for men, boron is not established. The only randomized study was negative; the positive indications come from an uncontrolled study with 8 men and from an experiment in women after boron deprivation that could not be replicated. For bone there is no randomized study with bone mineral density or fractures as the primary endpoint, only metabolic measurements and cross-sectional data, such as a correlation in 66 women with osteoporosis. The NIH describes the human data on bone as inconsistent.

For joints, the studies cover only two weeks, and they come from a manufacturer’s environment. The brain findings show that a boron deficiency could be harmful, not that supplements are useful beyond a normal diet. And as a general rule: as long as no specific function of boron in humans is known, the question of a requirement also remains open.

Status, approval and legal

Boron is available in food supplements in Germany; there is no authorized EU health claim. The BfR proposes a maximum of 0.5 mg boron per daily dose of a food supplement and recommends the notice “Not suitable for children and adolescents”, because their boron intake can reach the upper limit even without supplements. The value is a proposal, not a legal limit. Boron glycinate and boron bisglycinate are considered non-authorized novel foods in the EU. EFSA assessed calcium fructoborate in 2021 as safe for adults up to 220 mg per day, which corresponds to at most 6.4 mg boron. The studies used 2.5 to 10 mg boron per day; this is a statement about studies, not a recommendation. Boron is not on WADA’s 2026 Prohibited List.

Safety

In the usual amounts from food, boron is unproblematic. EFSA sets the tolerable upper limit for adults at 10 mg per day, the US authorities at 20 mg. Because a boron-rich diet and mineral water can in an unfavorable case already supply about 9 mg per day, there is little room left for supplements in the BfR’s view. In animal experiments, boron in high amounts damaged fetal development and the male reproductive organs; for this reason, pregnant and breastfeeding women, children and adolescents, and couples trying to conceive are cautious with supplements. Since boron raised estradiol in postmenopausal women, taking it in hormone-dependent diseases should be discussed with a doctor. Acute poisoning shows up as nausea, vomiting, diarrhea and skin rash; according to the NIH, only amounts of 15,000 to 20,000 mg become life-threatening. Even with the calcium fructoborate assessed by EFSA, adults together with food reach 9.6 to 9.9 mg boron per day, that is, within the range of the acceptable daily intake.

Sources

• BfR – proposed maximum levels for boron in foods including food supplements
• NIH Office of Dietary Supplements – Boron Fact Sheet
• Nielsen et al., FASEB J 1987 – boron, mineral and hormone metabolism in women
• Beattie & Peace, Br J Nutr 1993 – low-boron diet and boron supplementation
• Ferrando & Green, Int J Sport Nutr 1993 – boron in bodybuilders
• Naghii et al., J Trace Elem Med Biol 2011 – boron, hormones and inflammatory markers
• Penland, Environ Health Perspect 1994 – boron and brain function
• Pietrzkowski et al., Clin Interv Aging 2014 – calcium fructoborate for knee discomfort
• EFSA NDA Panel, EFSA J 2021 – calcium fructoborate as a novel food