Boron raised free testosterone 28% in a week, in 8 men

By David Beckwith

Evidence check, October 29, 2026. Updated November 2, 2026.

The claim: "10 mg of boron a day raises free testosterone in one week."

Our grade: Weak. In 8 men, free testosterone rose 28% and estradiol fell 39% after a week of 10 mg a day, and the numbers in the paper's table match the claim. Caveat: there was no comparison group, and the one randomized trial in men (19 bodybuilders, 2.5 mg a day for 7 weeks) found no change in testosterone, muscle or strength.

You're 40, scrolling late at night, and a reel says one cheap mineral "does more in 7 days than your entire supplement stack does in a month." The slide shows a study: 8 men, 10 mg of boron a day, free testosterone up 28%.

Is that number real?

It is. In a 2011 study from Iran, free testosterone in 8 healthy men went from 11.8 to 15.2 pg/mL after 7 days of 10 mg of boron a day [1]. What the reel leaves out is how the study was run, and what happened when other researchers tried it.

Where the claim came from

The reel is from the fitness account AestheticVillain on Facebook. Its slides say boron raises free testosterone, lowers SHBG (sex hormone binding globulin, the protein that holds testosterone so it can't act), lowers inflammation, makes vitamin D last longer and flushes out fluoride. "Three mechanisms. One mineral." It ends with a pitch for an ebook.

The idea is older than the reel. On Huberman Lab on December 12, 2022, the doctor Kyle Gillett told Andrew Huberman: "If you have a very high SHBG, boron can acutely help lower it usually in a dose of 5 to 12 milligrams per day. It's not really a sustained effect" [2]. In an earlier episode, on April 11, 2022, he gave the dose as "three to six milligrams, once to twice a day" [3].

Gillett's careful wording turns out to fit the data better than the reel does. Both rest on the same 8 men.

What free testosterone is, and why you want it

Most of the testosterone in your blood is held by proteins. In men, about half is gripped tightly by SHBG and can't get into cells. Most of the rest is held loosely by albumin, the most common blood protein, which lets go of it easily. Only about 2 to 3% floats free [13].

The free part is the part that can slip into muscle, brain and other cells and switch genes on. That is why doctors look at it when a man has the signs of low testosterone (low sex drive, low energy, losing muscle) but a normal total number. A man with high SHBG, common with age, can have a normal total and still not much free testosterone. The Endocrine Society's guideline says to measure free testosterone when SHBG is likely to be off [13].

Two cautions. Free testosterone is hard to measure well, and labs that test it directly often get it wrong; the best method is slow and expensive, so most labs calculate it from total testosterone, SHBG and albumin [13]. And more free testosterone in a man whose level is already normal has not been shown to build muscle or energy.

Does boron raise testosterone?

In the 8 men it did, and fast [1]. The men were 29 to 50, 41 on average, healthy, not on any supplement. On day 0 they came in fasting at 8 a.m., gave blood and took a dummy capsule of milk sugar with breakfast. From the next day they took a capsule of 10 mg of boron (as sodium tetraborate, a form of borax) with breakfast every day. On day 7 they gave blood again at 8 a.m.

After the week, free testosterone, the part not held by SHBG, was 28% higher. Estradiol, the main estrogen, was 39% lower. Total testosterone barely moved: 3.20 to 3.32 ng/mL (320 to 332 ng/dL, the unit US labs use), a change small enough to be chance.

So the claim is true to the table. Three things about the study keep it from settling the question.

There was no comparison group. Every man took boron, and "before" was a single blood draw on one morning. Free testosterone swings from day to day, and the study had no way to separate the boron from that swing.

It is small. With 8 men, one or two big responders can move the average.

It has not been repeated. In the 15 years since, we found no study that tested 10 mg a day again in men.

What happened to SHBG and estrogen?

SHBG fell, but only for a few hours [1]. On the first day of boron, the average across three blood draws over the next 6 hours was 29.7 nmol/L, against 32.2 at the same hours on the dummy day, a drop of 8%. After a week, morning SHBG was 33.0 before and 31.4 after, a change the study could not tell from chance. The reel's "SHBG dropped significantly" describes the first afternoon, not the week. That is what Gillett meant by "not really a sustained effect."

Estrogen went the other way in a longer study by the same lab. In 1997 the same researchers gave 18 healthy men the same 10 mg a day for 4 weeks [4]. Estradiol rose 42%, from 51.9 to 73.9 pmol/L, and testosterone only showed "a trend" upward. One week of boron lowered estrogen; four weeks raised it. Neither study had a comparison group, so neither can say which is the real effect.

Does it build muscle? The one randomized trial

The one trial that compared boron with a dummy pill found nothing [5]. In 1994, researchers gave 10 male bodybuilders aged 20 to 27 boron (2.5 mg a day) and 9 a dummy pill for 7 weeks, without telling them which. Both groups gained in total testosterone, lean mass, squat and bench press, by about the same amount. The training did that; the boron added nothing.

The dose was a quarter of the 10 mg in the 8 men, so this trial doesn't rule out a bigger dose. It does show that the most common supplement dose, 3 mg or less, has not been shown to help testosterone or strength.

Boron and inflammation: the placebo trial

The best evidence for boron is not about testosterone. In a 2015 trial in Romania, 78 people aged 40 to 60 with raised CRP and cholesterol took calcium fructoborate (a boron-sugar compound found in fruit) or a dummy pill for 30 days, at random and without knowing which [6]. The higher dose gave 3 mg of boron a day, the lower one 1.5 mg.

From Table 3 of Rogoveanu et al., 2015 [6]. Each group had 26 people.

All four fell more on boron than on the dummy pill. The 1.5 mg dose also lowered IL-6, MCP-1 and LDL, but not CRP. No one reported side effects. These are blood markers, not heart attacks, and the trial lasted a month, so nobody knows yet whether the drop lasts or matters for health.

The 8 men pointed the same way: after a week, CRP fell from 1.46 to 0.80 mg/L and IL-6 from 1.55 to 0.87 pg/mL, though with 8 people neither change could be told from chance [1].

What about fluoride, vitamin D and the other slides?

Fluoride: we found no study in people. The slide about it shows a 2004 paper that is a hypothesis about vitamin D and never mentions fluoride [8]. The fluoride idea comes from animal studies and old letters, not from trials.

Vitamin D: that 2004 paper proposes that boron slows the enzyme that breaks vitamin D down, but it has no data of its own [8]. The 8 men's vitamin D went from 35.8 to 38.4 nmol/L, a change the study could not tell from chance [1]. Small diet studies in which people first ate almost no boron saw vitamin D rise when boron came back [7], which says more about a low-boron diet than about adding pills.

"Requires an insulin spike to absorb": we found no study showing this. The body absorbs 85 to 90% of the boron it eats [9]; in the 1997 study, 84% of the dose came back out in urine [4].

"Cycle it to prevent mineral displacement": the studies show the reverse. In 12 older women who ate a low-boron diet for 119 days, adding 3 mg a day made them lose less calcium and magnesium in urine, not more [12].

The reel's warning that boron may shorten deep sleep: no study we found measured it.

Boron side effects and how much is safe

At supplement doses, trials have reported no side effects in men [1, 5, 6]. The limits are set from animal studies at high doses. The US upper limit for adults is 20 mg a day [9]; Europe's is 10 mg [10]. Most adults get about 1 mg a day from food [9]. Boric acid and borax powders are poisons when swallowed in large amounts and are not supplements.

For women, the picture is mixed. In a USDA trial, women near menopause took 2.5 mg a day for 60 days and, at another time, a dummy pill [11]. On boron, 21 of 46 had more hot flashes and night sweats, 10 had fewer, and 15 noticed no change. In older women, boron raised estrogen [12], so women on estrogen-blocking drugs or with an estrogen-sensitive cancer should ask their doctor first.

The reel says to take boron with vitamin D and magnesium. No study has tested that stack.

Our grade

Corrected November 2, 2026: one row in this table went from "Not supported" to Weak. We keep our lowest grade for good human evidence that points the other way, and the evidence here is too thin for that.

The case for the other side: the 8-man study measured free testosterone with the same lab and the same method on both days, the rise was large and statistically clear, and the share of testosterone that was free rose too, from 0.36% to 0.47%. Something happened in those men. One more caution: in healthy men about 2% of testosterone is free, so this lab's direct test read low on both days. The rise is the finding; the levels themselves are not ones to compare with your own lab report [13].

The bodybuilder trial used a quarter of the dose. A trial of 10 mg a day against a dummy pill has never been run, so the 8-man result has not been disproved either.

What would change the grade: a randomized trial of 10 mg a day against a dummy pill, in a few dozen men, measuring free testosterone, estradiol and SHBG at the same morning hour for at least a month. If free testosterone rose there too, this would become Promising.

What this means for you

Boron is cheap and safe at the doses studied, so trying it is a small bet. Here is how to make it a fair one.

Pick 3 mg a day. That is the dose with the placebo-controlled result, a CRP drop of about a third in 30 days [6], and the dose Gillett gives at the low end [3]. There is no evidence that one form beats another; the 8-man study used plain sodium tetraborate and the inflammation trial used calcium fructoborate [1, 6]. The 8 men took theirs with breakfast; no study shows you need a sugary meal or an insulin spike to absorb it.

If you want to try the 10 mg a day from the 8-man study, keep it to that and no more, which is Europe's upper limit [10].

Test, don't guess. Get free testosterone, total testosterone, estradiol and SHBG at the same morning hour before you start, and again after 1 to 4 weeks. One test before and one after is what the study did; two before is better, because free testosterone moves from day to day.

Or eat it. Boron is in fruit, nuts and beans. A cup (240 ml) of prune juice gives 1.4 mg, ½ cup of avocado (75 g) 1.1 mg and a small 42 g box of raisins 1.0 mg, together about 3.5 mg, the inflammation trial's dose [9]. A peach gives 0.8 mg and an apple 0.7 mg.

Keep the big levers first. In the bodybuilder trial, seven weeks of training raised total testosterone, muscle and strength in both groups [5]. Sleep, lifting and losing extra fat move testosterone more than any mineral; if two morning tests are truly low, our TRT evidence check covers what a doctor can offer.

So back to the reel: the 28% was real in 8 men. A cup of prune juice and half an avocado a day get you the dose that cut inflammation by a third in a month, and you'll know your own numbers in a few weeks.

What's next

The trial that would settle it is simple and cheap: 10 mg of boron a day against a dummy pill, in a few dozen men, for a month. We found none registered yet; when one reports, we'll update this page.

More on hormones: our evidence checks on TRT and heart attacks and hormone therapy for women.

Until then, a mineral that costs a few cents a day and sits in a cup of prune juice has one good trial behind it, and you can watch your own numbers to see whether it does more for you.

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