Boron: Benefits, Forms, Dosing, and Side Effects

Table of Contents

• Current view (reviewed 23 October 2026)
• Key safety points
• Brad's videos on this topic
• Overview
• Forms and Bioavailability
• Evidence for Benefits
• Recommended Dosing
• Safety and Side Effects
• Drug Interactions
• Dietary Sources
• References

Current view (reviewed 23 October 2026)

Brad describes studies showing potential benefits of small amounts of boron, including for bone health, brain function and the function of steroid hormones such as estrogen, testosterone and vitamin D (Brad, 7 Jan 2025). Boron is still not classed as an essential mineral, because science has not yet identified the enzymes or molecular pathways it uses, so neither the Food and Nutrition Board nor the World Health Organization has set a recommended intake (Brad, 7 Jan 2025). Brad's current guidance credits boron with extending the half-life of vitamin D and reducing the calcium lost in urine (Brad's current guidance, 14 Oct 2026). He includes a tiny amount of boron in his own multivitamin to cover his bases on top of a healthy diet, but says that just because he takes it does not mean it is right for you (Brad, 7 Jan 2025). In the US version, that amount is 1 mg of boron as boron glycinate (Brad's current guidance, 29 Sep 2026). His main warning about trace minerals is megadosing: almost all of them become toxic at megadose levels, so avoid supplements that hold hundreds of times more than you need (Brad, 7 Jan 2025).

Brad's videos on this topic

• 7 Jan 2025, Trace Minerals in Vitamins: What Are They and Is It a Fad?: trace minerals in a multivitamin help cover dietary gaps; boron is not essential but shows potential benefits, Brad takes a tiny amount, and megadoses are the main risk.

1. Overview

Boron is a trace element found naturally in plants, soil, and water. Bone, nails and hair hold more boron than other body tissues, and fat holds less ^[2]. Boron is not classified as an essential nutrient for humans, because research has not yet identified a clear biological function for it, and boron deficiency signs have not been firmly established in humans ^[2]. Consequently, no Recommended Dietary Allowance (RDA) or Adequate Intake (AI) has been established.

Small trials and diet studies suggest that boron may affect calcium metabolism, bone formation, brain function, insulin and energy metabolism, immunity, and the function of steroid hormones including vitamin D and estrogen ^{[1, 2, 4, 17]}. The World Health Organization estimates that an acceptable safe range of boron intakes for adults is 1–13 mg per day ^[6].

According to NHANES III data, median dietary boron intakes range from 0.87 to 1.35 mg/day in adults, 1.05 to 1.08 mg/day in pregnant women, and 0.75 to 0.96 mg/day in school-age children ^[2]. Vegetarians tend to have higher intakes because boron is plentiful in plant foods ^{[2, 7]}. The boron content of drinking water varies considerably by source ^{[2, 54]}; the median US concentration is 0.031 mg/L ^[2].

Most ingested boron is hydrolyzed to boric acid within the gastrointestinal tract, and the body absorbs approximately 85–90% of ingested boron ^{[2, 3]}. Boric acid is the main form of boron in blood, urine, and other body fluids ^{[2, 3]}. Blood boron changes little when intake rises, which suggests the body keeps boron steady mainly by raising urinary excretion, though the controls have not been identified ^{[2, 51]}. Boron is excreted mainly in the urine, with small amounts lost in feces, sweat, breath, and bile ^{[2, 4]}.

Boron status is not routinely measured in clinical practice. Most studies suggest that urinary boron levels track boron intake ^{[2, 48]}. Fasting plasma concentrations of boron in postmenopausal women range from 34 to 95 ng/mL (3.14 to 8.79 mcmol/L) ^{[2, 55]}.

2. Forms and Bioavailability

Supplements contain boron in many chemical forms, each bound to another molecule, so elemental boron is only part of the compound's weight ^[2]. The Supplement Facts label declares the elemental boron, not the weight of the whole compound ^[2]. Common amounts of elemental boron in dietary supplements range from 0.15 to 6 mg ^[2].

Common Supplement Forms

Bioavailability Considerations

No data are available on the relative bioavailability of the different supplemental forms of boron ^[2]. The one human data point is that sodium tetraborate raised plasma boron within 4–6 hours in a small study ^[2].

Researchers who study calcium fructoborate argue that sugar-borate molecules act differently from inorganic boron ^[13], and cell studies suggest it may damp inflammatory responses ^[49]. Most of the positive joint trials used calcium fructoborate ^[2], and the 2014 knee trial was funded by its maker ^[59], so it is unclear whether the form matters or was simply the one tested.

3. Evidence for Benefits

Bone Health

Boron's potential role in bone health is supported by multiple lines of evidence, though the data remain preliminary. Boron might affect bone through bone-building and bone-resorbing cells, steroid hormones, or calcium metabolism ^{[2, 49]}, and reviews link it to calcium metabolism and bone growth ^[23].

Calcium and mineral metabolism, depletion-repletion studies: In a metabolic-unit study, 12 postmenopausal women aged 48 to 82 ate a diet supplying about 0.25 mg of boron a day for 119 days and then took a 3 mg boron supplement daily (Nielsen et al., FASEB J, 1987) ^[16]. Boron markedly reduced urinary calcium and magnesium, and the drop appeared larger when dietary magnesium was low ^[16]. The authors judged these changes consistent with preventing calcium loss and bone demineralization ^[16]. A low-boron diet (0.25 mg boron/2,000 kcal) might also raise urinary calcium and magnesium and lower serum estrogen in postmenopausal women ^{[2, 6]}.

Vitamin D levels: Low boron intakes (0.23 mg boron/2,000 kcal) appear to reduce plasma calcium and serum 25-hydroxyvitamin D and raise serum calcitonin and osteocalcin in men and women, changes that could affect bone mineral density ^{[2, 6]}. In 8 healthy men, a week of 10 mg of boron a day raised vitamin D levels ^[5]. A 2004 hypothesis paper proposed that boron raises 25-hydroxyvitamin D by slowing its breakdown by the enzyme 24-hydroxylase, citing small pilot studies (Miljkovic et al., Med Hypotheses, 2004) ^[19]. Brad's current guidance follows this idea; the paper presented it as a hypothesis ^[19].

Bone mineral density, clinical trial in female athletes: A placebo-controlled clinical trial in 17 female athletes (mean age 19.8 years) and 11 sedentary females (mean age 20.3 years) found that 3 mg/day of boron supplementation for 10 months significantly reduced serum phosphorus levels and increased serum magnesium levels in sedentary females, changes often associated with increased bone mineral density ^{[2, 20]}. However, supplementation did not directly affect bone mineral density in this study ^[2].

Bone mineral density, observational evidence: An observational study of 134 Korean women (average age 41 years) found that boron intakes (mean of 0.9 mg/day) were not significantly correlated with bone mineral density in the lumbar spine or femoral regions ^[22]. However, the mean intake was relatively low, and the study was cross-sectional, limiting causal inference ^[22].

Animal evidence: Animal studies provide stronger mechanistic support for boron's role in bone health. Boron deficiency in animals causes abnormal limb development, delayed maturation of growth plates, and decreased bone strength, bone volume fraction, and trabecular thickness ^{[2, 3]}. Supplementation in animals improves some measures of bone strength compared to those consuming usual or low amounts of boron ^{[24, 25, 26]}. A study in non-obese diabetic mice found that boron supplementation improved bone health parameters ^[27].

Phosphorus lowering: A placebo-controlled trial in athletic and sedentary women also found lower serum phosphorus with boron than with placebo, an effect that exercise training lessened (Meacham et al., Am J Clin Nutr, 1995) ^[28]. The authors judged the effect on mineral status modest ^[28].

Synthesis: Boron may support bone health through indirect routes, such as lower urinary calcium and magnesium losses and effects on vitamin D and hormones ^{[2, 16]}. However, direct evidence that boron supplementation improves bone mineral density in humans is lacking. The strongest human evidence comes from depletion-repletion studies at very low intakes, and a 2014 review concluded that intakes of less than 1.0 mg a day appear to block boron's benefits ^[17]. This points to adequate intake rather than high-dose supplements.

Osteoarthritis

Small studies have tested boron for osteoarthritis, the joint disease in which cartilage wears down. The proposed mechanism is reduced inflammation ^{[2, 30]}.

Epidemiological evidence: A 1994 review reported that where boron intakes are usually 1.0 mg or less a day, the estimated incidence of arthritis is 20 to 70%, compared with 0 to 10% where intakes are usually 3 to 10 mg (Newnham, Environ Health Perspect, 1994) ^[29]. This ecological correlation has many possible confounders, but it gave the first rationale for clinical trials.

First controlled trial: In a small pilot trial, 20 people with osteoarthritis younger than 75 years (mean age about 65 years) took 6 mg of boron a day or placebo for 8 weeks ^[2]. In this double-blind trial, 50% of those taking boron improved, compared with only 10% taking placebo ^[29]. The small sample limits the strength of this finding.

Calcium fructoborate, open-label study: An 8-week study in 20 patients with mild to moderate or severe osteoarthritis found that 6 mg/day of boron as calcium fructoborate for mild to moderate disease, or 12 mg/day for severe disease, reduced joint rigidity and ibuprofen use for pain and increased mobility and flexibility ^[2]. However, this study was very small, not blinded, and not placebo-controlled ^[2].

Calcium fructoborate, inflammatory markers: A double-blind, placebo-controlled trial gave 1.5, 3, or 6 mg/day of boron as calcium fructoborate, or placebo, for 2 weeks to people with knee osteoarthritis aged 59–68 years; 60 completed the study (Scorei et al., Biol Trace Elem Res, 2011) ^{[2, 30]}. Calcium fructoborate improved inflammatory markers, including C-reactive protein (CRP) and fibrinogen, compared with placebo, and no serious adverse events were reported ^{[2, 30]}. The trial was double-blind and dose-ranging, but 2 weeks is short.

Calcium fructoborate, knee discomfort (first study): An earlier study reported that calcium fructoborate, 110 mg twice per day, improved knee discomfort within the first 14 days ^[11].

Calcium fructoborate, knee discomfort (second study): In a double-blind, placebo-controlled trial in 60 adults (mean age 50 years) with self-reported knee discomfort, calcium fructoborate at 110 mg twice per day, providing 6 mg/day of boron, lowered McGill pain scores more than placebo by day 7, and both McGill and WOMAC scores by day 14 (Pietrzkowski et al., Clin Interv Aging, 2014) ^{[2, 11]}. FutureCeuticals, which employed three of the authors, funded the study and supplied the calcium fructoborate ^[59].

Synthesis: The osteoarthritis data are suggestive but limited by small samples (20 to 60 participants) and short durations (2 to 8 weeks) ^[2]. The 2014 knee trial was also funded by the manufacturer ^[59]. Calcium fructoborate providing about 6 mg of boron a day has the most consistent results for inflammatory markers and knee discomfort ^[2]. Confirmation from more controlled trials is needed before boron can be recommended for osteoarthritis ^[2].

Cognitive Function

Diet studies suggest that boron may play a role in human brain function and cognitive performance ^[33].

Depletion-repletion studies, brain wave activity: Penland and colleagues ran three studies in healthy older men and women, comparing diets with about 0.25 and about 3.25 mg of boron per 2,000 kcal a day (Penland, Environ Health Perspect, 1994) ^[33]. In two of the three, the low-boron diet increased the share of low-frequency brain wave activity and decreased higher-frequency activity, a pattern also seen with general malnutrition and heavy metal toxicity ^[33].

Depletion-repletion studies, cognitive performance: In the same studies, the low-boron diet led to poorer performance on tasks of manual dexterity, eye-hand coordination, attention, perception, and short-term and long-term memory ^{[33, 34]}. A separate study varied magnesium and boron independently in 13 postmenopausal women and found that marginal shortfalls of each changed brain wave activity (Penland, Magnes Res, 1995) ^[35].

Mechanism: Boron may affect cell membrane function, which could influence nerve signaling ^{[17, 33]}. The precise mechanisms by which boron affects cognitive processes remain unclear.

Deficiency effects: Limited data suggest that boron deficiency might affect brain function by reducing mental alertness and impairing executive brain function ^{[1, 2, 6]}. These findings come primarily from controlled dietary restriction studies rather than observations in clinical populations.

Synthesis: The cognitive evidence comes from diet studies showing poorer function at very low intakes, not from trials of supplements taken on top of an adequate diet ^{[2, 33]}. There is no evidence that boron supplements improve cognition in people who already eat enough boron. A review of these studies also found little support for claims that physiologic amounts of boron ease menopause symptoms ^[34].

Testosterone and Steroid Hormones

Boron has been sold to athletes as a way to raise testosterone ^[36], but the evidence is mixed and the most rigorous study was negative.

Postmenopausal women, estrogen and testosterone: In Nielsen's 1987 metabolic-unit study, a 3 mg/day boron supplement given after a low-boron diet markedly raised serum 17β-estradiol and testosterone in postmenopausal women, more so when dietary magnesium was low (Nielsen et al., FASEB J, 1987) ^[16]. One hypothesis is that boron slows the enzymes that break down estradiol and vitamin D ^[19].

Short-term high-dose study in men: In a 2011 study, 8 healthy men took 10 mg of boron a day for a week (Naghii et al., J Trace Elem Med Biol, 2011) ^[5]. By six hours after the first capsule, sex hormone-binding globulin (SHBG) had dropped, and after a week free testosterone had risen and estradiol had fallen ^[5]. The study was very small, lasted one week, and had no separate placebo group ^[5].

Bodybuilders, no effect on testosterone or performance: In a placebo-controlled trial in male bodybuilders, a 2.5-mg boron supplement taken for 7 weeks did not change testosterone, strength, or lean body mass (Green and Ferrando, Environ Health Perspect, 1994) ^[36]. This negative controlled trial undermines testosterone-boosting claims ^[36].

Estrogen changes: Estradiol rose with 3 mg a day in postmenopausal women ^[16] and with 10 mg a day for 4 weeks in healthy men, from 51.9 to 73.9 pmol/L ^{[37, 48]}. Yet in the 2011 study in men it fell after a week of 10 mg a day ^[5]. A 2004 paper noted that boron may also raise estradiol in postmenopausal women on hormone replacement therapy ^[19], so women on hormone therapy may want to ask their doctor before taking boron. Given these estradiol rises, the same check makes sense after a cancer that grows in response to estrogen ^{[16, 37, 19]}.

Synthesis: Boron's effects on steroid hormones are inconsistent across studies and appear to depend on dose, duration, sex, and baseline diet ^{[5, 16, 36, 37]}. The one positive testosterone study in men used 10 mg a day for a week in 8 men without a separate placebo group ^[5]. The placebo-controlled bodybuilder trial (2.5 mg a day for 7 weeks) found no benefit for testosterone or body composition ^[36]. Boron should not be taken as a testosterone booster based on current evidence ^[36].

Cancer

Preliminary epidemiological evidence suggests a possible inverse association between dietary boron intake and certain cancer risks, though no clinical trials have evaluated boron for cancer prevention or treatment ^[2].

Prostate cancer: In a US analysis of NHANES III data comparing 95 men with prostate cancer and 8,720 controls, men in the highest quartile of boron intake had lower odds of prostate cancer than those in the lowest (odds ratio 0.46, 95% CI 0.21 to 0.98) (Cui et al., Oncol Rep, 2004) ^[38]. The authors urged caution because of the small number of cases and the cross-sectional design ^[38]. An observational study in Turkey evaluated two criteria for prostate cancer risk, prostate size and prostate specific antigen (PSA) levels (Muezzinoglu et al., Biol Trace Elem Res, 2011) ^[39]. Men with higher boron intakes (about 6 mg/day) had significantly smaller prostate glands than men who consumed less boron (0.64–0.88 mg/day), though PSA levels did not differ significantly between the two groups ^[2].

Lung cancer in women: In a case-control study of 763 women with lung cancer and 838 healthy women, the odds of lung cancer rose as boron intake fell, and women in the lowest quartile had an odds ratio of 1.95 (95% CI 1.42 to 2.68) compared with the highest (Mahabir et al., Am J Epidemiol, 2008) ^[40]. The lowest quartile was less than 0.78 mg/day and the highest more than 1.25 mg/day ^[2].

Cervical cancer: In an observational study in Turkey, women in boron-rich areas (mean intake 8.41 mg/day) had no cervical smear findings suggesting cancer, while 15 women from boron-poor areas (1.26 mg/day) did (Korkmaz et al., Environ Toxicol, 2007) ^[41].

Potential mechanisms: In prostate cancer cells, boric acid at the blood level reported in men at the US mean boron intake activated cell stress pathways (eIF2α/ATF4 and ATF6), and a follow-up study linked this to Nrf2 and antioxidant genes (Kobylewski et al., Biol Trace Elem Res, 2017; Yamada and Eckhert, Biol Trace Elem Res, 2019) ^{[42, 43]}. A review also reported that calcium fructoborate inhibited breast cancer cells in the laboratory ^[50]. These are cell studies only.

Synthesis: The cancer data are exclusively observational and preliminary. No clinical trials have tested whether boron supplementation prevents cancer. These associations may reflect confounding from overall fruit and vegetable intake (which is the major dietary source of boron) rather than boron itself. Whether boron itself has any effect on cancer risk is unknown ^{[2, 4]}.

Vaginal Infections (Topical Use)

Boric acid suppositories are used intravaginally for vaginal infections. A 2018 review noted that intravaginal boric acid has been used safely for candida vulvovaginitis and bacterial vaginosis, and found four case reports, but no randomized trials, of its use for Trichomonas vaginalis, at doses from 600 mg on alternate nights to 600 mg twice a day (Thorley and Ross, Sex Transm Infect, 2018) ^[12]. This is a topical pharmaceutical use and is distinct from oral boron supplementation.

Inflammation

Several lines of evidence suggest boron may have anti-inflammatory effects, though the data come from small studies and are not conclusive.

Osteoarthritis-related inflammation: In the 2-week Scorei trial, calcium fructoborate at 1.5, 3, and 6 mg/day of boron improved inflammatory markers, including CRP and fibrinogen, compared with placebo ^{[2, 30]}. These markers are also linked to cardiovascular risk and general inflammation.

Proinflammatory cytokines: In the 2011 study in 8 healthy men, 10 mg/day of boron lowered all three inflammatory markers measured, including hsCRP and TNF-α ^[5]. The small sample and one-week duration limit conclusions.

Theoretical mechanisms for calcium fructoborate: Researchers working on calcium fructoborate argue that its effects come from the sugar-borate molecule rather than boron alone ^[13], and cell studies suggest it may protect against inflammatory responses ^[49]. However, these proposed mechanisms remain largely theoretical.

Other areas under investigation: A 2018 review lists wound healing and immune function among areas of study, but notes that findings have been mixed ^[4].

Synthesis: Boron may reduce markers of inflammation, particularly as calcium fructoborate at 3–6 mg/day. However, how much this matters clinically, and whether it translates to meaningful health outcomes beyond the context of osteoarthritis is unknown.

4. Recommended Dosing

No Established Daily Requirement

The Food and Nutrition Board (FNB) of the National Academies found the existing data insufficient to derive an RDA, Adequate Intake (AI), or Estimated Average Requirement (EAR) for boron ^[2]. The World Health Organization estimates that an acceptable safe range of boron intakes for adults is 1–13 mg per day ^[6]. Because boron does not have an RDA, it also does not have a Daily Value (DV) for food labeling purposes ^[2].

Tolerable Upper Intake Levels (ULs)

The FNB based the boron ULs on levels linked to reproductive and developmental effects in animals ^[2]:

*Breast milk, formula, and food should be the only sources of boron for infants ^[2].

Note: The European Food Safety Authority (EFSA) sets a lower adult upper limit of 10 mg/day ^[56], compared to the US UL of 20 mg/day ^[2]. The WHO acceptable range is 1–13 mg/day ^[6].

Doses Used in Clinical Trials

Practical Dosing Guidance

General supplementation (to fill dietary gaps): No intake has been set, so there is no evidence-based target dose ^[2]. The depletion-repletion studies used 3 mg a day ^[16], and a 2014 review concluded that intakes of less than 1.0 mg a day appear to block boron's benefits ^[17].

Osteoarthritis or joint support: Trials used about 6 mg a day, mostly as calcium fructoborate, and 12 mg a day for severe disease ^[2]. These were small, short trials ^[2], and the severe-disease dose is above Europe's upper limit of 10 mg a day ^[56].

Bone health support: No trial has shown that boron supplements raise bone density ^{[2, 20]}.

Dr Brad Stanfield's MicroVitamin includes 1 mg of boron as part of a bone density support trio alongside Vitamin K2 MK-7 (90 mcg) and Vitamin D3 (1,000 IU) — designed to work synergistically to support calcium metabolism and bone health.

5. Safety and Side Effects

Common Side Effects

Boron supplement trials were small and brief, so data on common side effects are limited. In the 2-week calcium fructoborate trial, no serious adverse events were reported ^[30].

Estrogen Elevation

Boron raised estradiol in postmenopausal women taking 3 mg a day ^[16] and in healthy men taking 10 mg a day for 4 weeks ^[37], though estradiol fell in another one-week study in men ^[5]. Boron may also raise estradiol in women using hormone replacement therapy (HRT), so women on HRT may want to talk to a doctor before taking boron ^[19]. Because estradiol can rise ^{[16, 37, 19]}, the same applies to:

• Anyone treated for a breast, uterine or ovarian cancer that grows in response to estrogen
• Women taking tamoxifen or aromatase inhibitors
• Men with conditions sensitive to estrogen levels

Phosphorus Lowering

In a 10-month placebo-controlled trial in young women, 3 mg/day of boron lowered serum phosphorus ^{[2, 20]}. A second report in athletic and sedentary women found lower serum phosphorus with boron and judged the effect on mineral status modest ^[28].

High-Dose Effects

Boron is toxic at high concentrations ^[15]. Boron toxicity can cause ^[2]:

• Dermatitis and skin rash
• Hair loss (alopecia)
• Loss of appetite (anorexia)
• Indigestion and gastrointestinal discomfort
• Headache, restlessness, and weariness

Acute Toxicity

Swallowing boric acid or borax (sodium borate), found in some household cleaning products and pesticides, has been linked to these symptoms ^[2]:

• Nausea, vomiting, diarrhea
• Skin flushing and rash
• Excitation, restlessness, or depression
• Convulsions and seizures
• Hypothermia
• Renal injury
• Vascular collapse

In a review of 784 boric acid ingestions at two regional poison centers, 88.3% of patients had no symptoms and none developed severe toxicity; the most common symptoms were vomiting, abdominal pain, and diarrhea ^[44]. The amount of boron consumed in reported accidental ingestion cases ranged from 18 to 9,713 mg, and most cases involved children younger than 6 years ^[2]. In infants, high boron intakes have caused anemia, seizures, erythema, and thin hair ^[2]. Extremely high doses of boron can be fatal: 15,000 to 20,000 mg (15 to 20 grams) can cause death in adults ^{[2, 3]}. If someone has a seizure, collapses, or becomes very unwell after swallowing boric acid or borax, call your local emergency number (111 in NZ, 000 in Australia, 911 in the US, 999 in the UK) or go to the emergency department.

No data are available on adverse effects of high boron intakes specifically from food or water ^[2]. The toxicity data come from accidental ingestion of concentrated boron compounds (cleaning products, pesticides), not dietary sources.

Reproductive and Developmental Toxicity

The FNB set the boron ULs from reproductive and developmental effects seen in animals ^[2]. In rats, high doses of boric acid damaged the testes, blocking sperm release at lower doses and causing testicular atrophy at higher doses, and the atrophy did not recover ^[57].

Special Populations

Pregnancy and lactation: The UL for pregnant and lactating women aged 19+ is 20 mg/day (same as non-pregnant adults). For those aged 14–18, the UL is 17 mg/day ^[2]. The median dietary boron intake in lactating women is 1.27 mg/day, and in pregnant women 1.05–1.08 mg/day ^[2]. Given the lack of established benefit during pregnancy and the theoretical reproductive concerns from animal studies, supplementation during pregnancy should be discussed with a healthcare provider.

Children: ULs are lower for children (3 mg for ages 1–3, 6 mg for ages 4–8, 11 mg for ages 9–13, 17 mg for ages 14–18). Infants should receive boron only through breast milk, formula, and food, not supplements ^[2]. Boron concentrations are approximately 0.27 mg/L in breast milk and 0.33 mg/L in cow's milk ^[2].

Kidney disease: Boron is excreted mainly in the urine, and the kidneys regulate boron balance ^{[2, 51]}. In a 2026 case report of boric acid poisoning in a woman with chronic kidney disease, the authors thought impaired kidney clearance prolonged her exposure ^[58]. People with kidney disease should ask their doctor before taking boron.

6. Drug Interactions

Boron is not known to have any clinically relevant interactions with medications ^[2]. This distinguishes boron from many other supplemental minerals (e.g., magnesium, calcium, iron, zinc) that can chelate drugs and reduce their absorption.

However, because boron changed estradiol and testosterone levels in small studies ^{[5, 16, 37]}, interactions with hormone treatments are theoretically possible:

• Hormone replacement therapy (HRT): Boron may raise estradiol in women using HRT ^[19]. Whether this adds to estrogen-related side effects is unknown.
• Tamoxifen and aromatase inhibitors: Boron's effect on estradiol could, in theory, work against these anti-estrogen cancer treatments. Women taking these medications for breast cancer treatment or prevention should consult an oncologist before supplementing boron.
• Testosterone replacement therapy: Boron's effects on testosterone are inconsistent ^{[5, 36]}. An interaction with TRT has not been studied.
• Oral contraceptives: Given the potential estrogenic effects, an interaction is theoretically possible though not documented.

These are theoretical concerns based on boron's observed hormonal effects rather than documented pharmacokinetic or pharmacodynamic drug interactions. Nevertheless, caution is warranted for individuals on hormone-modifying therapies. If you take prescription medicines, check with your doctor or pharmacist before starting.

7. Dietary Sources

Plant foods, including fruit, tubers, and legumes, contain the most boron ^{[2, 53, 54]}, and nuts are also rich sources ^{[7, 47]}. The amount of boron in plant foods depends somewhat on the boron content of the soil and water where they were grown ^{[2, 52]}. Areas of the world with limited boron in the soil include Brazil, Japan, and most of the United States, mainly because of high levels of rainfall, which leaches boron out of the soil. In contrast, arid regions, including California and parts of Turkey, Argentina, Chile, Russia, China, and Peru, have higher boron concentrations in soil and water ^{[2, 46]}.

Top Food Sources (Per Serving)

Sources: NIH ODS ^[2], drawing on ^{[7, 53]}.

Australian Food Analysis

In an analysis of 66 foods eaten in Australia, the main sources of boron were nuts, dried fruits, legumes, and fresh vegetables and fruits, and a group of Australians averaged 2.23 mg/day of boron (Naghii et al., J Am Coll Nutr, 1996) ^[47].

Practical Notes on Dietary Boron

• Vegetarians tend to have higher boron intakes than non-vegetarians because boron is plentiful in plant foods ^[2]. In a large US survey, median intakes were 1.30 mg/day for vegetarian men and 1.00 mg/day for vegetarian women, compared with 1.02 and 0.83 mg/day for all men and women ^[7].
• Main dietary sources in the US are coffee, milk, apples, dried and cooked beans, and potatoes, not because these are the richest sources per serving, but because Americans consume large amounts of these foods ^{[2, 7, 52]}.
• Among toddlers, 38% of boron intake comes from fruits and fruit juices and 19% from milk and cheese ^{[2, 3]}.
• For adolescents, milk and cheese products account for 18–20% of boron intakes ^{[2, 3]}.
• For adults, beverages, especially instant coffee, represent the largest dietary source of boron ^{[2, 3]}.
• Wine, cider, and beer also contain boron ^{[2, 6]}.
• Water contributes variable amounts depending on the source ^[54]. The median US drinking water concentration is 0.031 mg/L ^[2], and at some locations water may supply most of a person's dietary boron ^[54].
• Animal foods (meat, poultry, fish, dairy) contain very little boron. Tuna has only 0.05 mg per 3 oz serving, chicken breast 0.03 mg per half breast, and whole milk 0.04 mg per cup ^[2].
• USDA FoodData Central does not list boron content of foods, so available data on boron in foods are limited and come from specialized analyses ^[2].
• Food-first approach: Eating more fruits, vegetables, nuts, and legumes raises boron intake, and a 2014 review called such a diet a reasonable way to increase it ^[17].