3–10 mg/day in studies.
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Boron is a trace mineral present in soils, plants, and, in small amounts, in animal and human tissues; its "essential" status for humans has not been formally established (unlike iron, zinc, selenium, or calcium), but experimental and epidemiological observations indicate that it has relevant physiological functions in bone metabolism, hormonal modulation, and joint processes, which places it in an intermediate category between an essential nutrient and a useful micronutrient with no clear clinical requirement.
The most concentrated dietary sources are fruits (especially raisins, dates, apples, pears, grapes, prunes), nuts (especially almonds and hazelnuts), legumes, avocado, and coffee; typical Western diets provide between 0.5 and 2 milligrams of boron per day, an amount that varies and is often below the hypothetically optimal figures (3-10 mg/day according to nutritional hypotheses) that have generated interest in specific supplementation.
The indication with the strongest mechanistic basis is bone health: boron modulates the activity of vitamin D, improves renal retention of calcium and magnesium, and influences bone metabolism through several mechanisms; several studies have documented improvements in biochemical bone markers with supplementation at 3-6 milligrams per day for weeks to months, an indication consistent with epidemiological observations that associate low boron intake with a higher risk of osteoporosis in some cohorts.
Several small studies have documented mild modulation of steroid hormones (free testosterone, estradiol, dihydrotestosterone) with boron supplementation at 6-10 mg/day for weeks: the changes are quantitatively modest but statistically significant in some studies, an observation that has generated popularity in the male fitness world, although the clinical translation into improvements in body composition or performance is marginal.
In osteoarthritis, epidemiological studies associate regions with higher dietary boron intake with a lower prevalence of osteoarthritis (comparative data among Jamaica, the United States, Europe, and Mauritius); small clinical trials with supplementation at 6 mg/day for weeks have documented modest improvements in pain and joint function, preliminary but consistent data.
In cognition, experimental studies with controlled dietary deprivation have shown decreased performance on attention and memory tasks that is restored with supplementation, an observation that suggests a relevant, although modest, cognitive role.
The doses studied as a supplement range between 3 and 10 milligrams per day, divided into one or two doses with or without food; the most common commercial forms are boron citrate, boron glycinate, and mineral chelates; the tolerable upper limit established by regulatory agencies is 20 mg/day in adults, a prudent figure based on toxicity data from environmental overexposure and not on strict nutritional supplementation data.
Generally well tolerated at the usual supplemental and dietary doses; the adverse effects at high doses or from environmental overexposure (limited to people in the boron industry) include digestive discomfort, headache, skin irritation, and, in extreme cases, reproductive toxicity documented in animals; the usual supplemental doses are far below these toxic levels; people with serious kidney disease should exercise caution because of reduced excretion; in pregnancy and breastfeeding it is recommended not to exceed the usual dietary amounts (animal data suggest possible teratogenicity only at doses several times higher than nutritional ones); boron should not be confused with industrial boric acid (used as a pesticide and as a topical antiseptic), which has a different use profile and different safety considerations; complete multivitamins typically contain 100-500 micrograms of boron, a modest but useful amount; specific boron supplements at 3-6 mg/day are a reasonable option for people with diets low in fruits, nuts, and legumes, which naturally provide boron.
Information, not medical advice. Scientific evidence reflects the quality of the studies.