Boron: What It Is and How It Works

Boron is a trace element that most people have never thought about, yet it turns up in testosterone boosters, joint formulas and bone-health supplements. It is not officially classed as essential for humans, but it clearly has biological effects. Here is what the research says about how boron works and whether it deserves a place in an athlete's supplement cupboard.

What boron is

Boron is a light element that, in food and the body, exists mainly as boric acid and borate compounds. Plants need it for cell-wall structure, which is why fruit, vegetables, nuts, pulses, wine and coffee are the main dietary sources. Animal foods contain very little.

Unlike iron or zinc, boron has no established recommended daily intake. Neither the UK nor the European Food Safety Authority has defined a deficiency syndrome, because no specific enzyme or protein requiring boron has been identified in humans. It is therefore described as a possibly beneficial or ultra-trace element.

Absorption from food and supplements is efficient — most ingested boron passes into the blood within hours — and the kidneys excrete the excess quickly in urine. As a result, the body does not store large amounts, apart from modest concentrations in bone, nails and hair.

Typical intakes in the UK are estimated at around 1–2 mg per day, higher in people who eat lots of fruit, vegetables and nuts. Vegetarians generally consume more boron than meat eaters.

How boron acts in the body

Research in animals and humans suggests boron influences how the body uses several other nutrients and hormones. The mechanisms are not fully mapped, but several consistent observations have emerged from the literature summarised by Pizzorno in 2015.

• Bone metabolism: boron appears to reduce urinary losses of calcium and magnesium and to support the activity of vitamin D.
• Vitamin D: it may slow the breakdown of the active form of vitamin D, effectively prolonging its half-life.
• Sex hormones: in some studies boron raised levels of oestradiol and free testosterone, possibly by lowering sex hormone-binding globulin (SHBG).
• Inflammation: small trials have reported falls in markers such as C-reactive protein and interleukin-6.
• Cell signalling: boron binds to molecules with cis-hydroxyl groups, which may explain some of its interactions with hormones and energy metabolism.

An early study by Nielsen and colleagues in postmenopausal women found that adding boron to a low-boron diet reduced urinary calcium loss and increased circulating oestradiol and testosterone. This study is often cited, but it involved a small number of women who had first been made boron-depleted.

A 2011 study by Naghii's group in healthy men reported that one week of 10 mg boron daily lowered SHBG and raised free testosterone, with reductions in some inflammatory markers. The sample was small and the effect has not been confirmed in large, long-term trials.

Boron and athletic performance

Boron's reputation as a testosterone booster in bodybuilding circles dates back to the early 1990s. However, the most direct test, a trial by Ferrando and Green in male bodybuilders, found that 2.5 mg per day for seven weeks did not increase lean body mass, strength or total testosterone compared with placebo.

Both groups in that study improved because they were training, which illustrates a recurring problem: in a well-designed trial, training effects tend to swamp anything a trace element supplement might add.

The free testosterone shifts reported in other studies are modest and short-term. There is no good evidence that they translate into more muscle, faster recovery or better performance in healthy athletes with normal hormone levels.

A more realistic potential benefit concerns bone health, particularly in athletes at risk of low bone density such as female endurance runners or those with low energy availability. Even there, calcium, vitamin D and adequate energy intake are the priorities, and boron's role remains supportive at best.

Dose, forms and safety in the UK

Supplements typically provide 1–3 mg of boron per day as sodium borate, boric acid, calcium fructoborate or boron citrate/glycinate. Studies have rarely compared forms head-to-head, and all are well absorbed.

At very high intakes, boron is toxic: nausea, vomiting, diarrhoea and skin rashes have been reported, and animal studies show effects on fertility and fetal development. Boric acid itself is classified in Europe as toxic for reproduction, which is why upper limits are conservative.

Pregnant women should avoid boron supplements beyond normal dietary intake. People with kidney disease should also be cautious, because excretion depends on kidney function. Anyone considering boron as part of hormone-related treatment, such as for menopausal symptoms, should discuss it with their doctor.

Who might consider boron

For most people, a diet rich in fruit, vegetables, nuts and pulses provides plenty of boron, and a supplement is unlikely to add much. A handful of almonds, a portion of dried apricots or an avocado each contain meaningful amounts.

People with very low fruit and vegetable intake, or those in specific clinical trials for osteoarthritis or bone health, are the groups most often studied. Even in these groups the evidence is preliminary.

Many multivitamin and mineral products already contain 1–2 mg of boron, so adding a separate supplement may push intake higher than intended. Check every label in your cupboard before buying another product.

Boron is not prohibited in sport. Because it often appears in so-called testosterone boosters alongside herbal extracts of uncertain quality, athletes subject to testing should prefer simple, batch-tested formulations.

Editorial conclusions

Boron is a trace element with real but subtle effects on bone mineral metabolism, vitamin D and sex hormone binding. It is not formally essential, and no deficiency disease has been defined.

The best controlled study in athletes found no improvement in muscle mass, strength or testosterone, so boron should not be viewed as an anabolic supplement. Its potential lies more in general and bone health.

Stay well below the UK safe upper level of 9.6 mg per day, count boron in multivitamins and avoid supplements in pregnancy unless advised by a clinician.

If this topic interests you, see our pieces on magnesium for athletes, vitamin D testing in the UK and how SHBG affects free testosterone.

References

1. Ferrando AA, Green NR. The effect of boron supplementation on lean body mass, plasma testosterone levels, and strength in male bodybuilders. Int J Sport Nutr. 1993;3(2):140–149.
2. Green NR, Ferrando AA. Plasma boron and the effects of boron supplementation in males. Environ Health Perspect. 1994;102(Suppl 7):73–77.
3. Naghii MR, Mofid M, Asgari AR, et al. Comparative effects of daily and weekly boron supplementation on plasma steroid hormones and proinflammatory cytokines. J Trace Elem Med Biol. 2011;25(1):54–58.
4. Nielsen FH, Hunt CD, Mullen LM, Hunt JR. Effect of dietary boron on mineral, estrogen, and testosterone metabolism in postmenopausal women. FASEB J. 1987;1(5):394–397.
5. Pizzorno L. Nothing boring about boron. Integr Med (Encinitas). 2015;14(4):35–48.
6. Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals. London: Food Standards Agency; 2003.