Verdict: Interesting hormone data from one tiny study, no proven benefit for testosterone, muscle or VO2max
Safety: Safe at food-like doses; upper limit 20 mg a day (US) or 10 mg a day (EU); high doses are toxic
Key takeaways
The best-known boron study gave 10 mg a day to just eight men for one week, with no placebo group, and found higher free testosterone
A 7-week placebo-controlled trial in bodybuilders found no effect of boron on testosterone, lean mass or strength
Boron does not raise VO2max, and the upper intake limit is 20 mg a day in the US and 10 mg a day in the EU
Boron sits in many "testosterone booster" formulas, usually next to zinc, magnesium and a herbal extract. Searches for "boron testosterone" and "boron benefits for men" keep rising, mostly on the back of one small study from 2011. Here is what that study actually did, what the other evidence says, and why boron is not a VO2max supplement.
What it is
Boron is a trace element found in plant foods such as fruit, vegetables, nuts, legumes, coffee and wine. It is not officially an essential nutrient for humans, so there is no recommended daily intake, but it seems to play a role in bone, vitamin D and steroid hormone metabolism. Supplements usually provide 3–10 mg as sodium borate, boron citrate or boron glycinate.
Does it raise VO2max?
No. VO2max is limited mainly by how much oxygen the heart can pump and the blood can carry (see what limits VO2max). Boron does not change heart size, blood volume or haemoglobin, and no trial has shown an effect on VO2max or aerobic capacity. Testosterone itself is linked to haemoglobin, but boron has not been shown to move testosterone enough to matter (see testosterone, endurance training and VO2max).
Does it improve endurance performance?
There is no evidence that it does. The question that gets studied is testosterone, so it is worth looking closely at those trials.
Naghii et al., 2011 — eight men, one week
In this study (J Trace Elem Med Biol, 2011), eight healthy men took 10 mg of boron a day with breakfast. Blood samples were taken before and during the first day, and again after one week. After a week, mean free testosterone rose and estradiol fell significantly, and dihydrotestosterone, cortisol and vitamin D were higher. Within hours of the first dose, sex hormone binding globulin (SHBG) and inflammatory markers (hsCRP, TNF-alpha) decreased.
The limitations are big:
- Eight participants. Random variation alone can move hormone averages in such a small group.
- No placebo group. Each man was compared only with himself, so time, season or lab effects cannot be ruled out.
- One week. It says nothing about whether any change lasts, or whether it affects muscle or performance.
- Free testosterone, not total. A drop in SHBG can raise free testosterone without the body producing more.
Green and Ferrando, 1994 — bodybuilders, seven weeks
A placebo-controlled trial (Environ Health Perspect, 1994) gave 2.5 mg of boron a day or placebo to 19 young male bodybuilders for 7 weeks. Both groups gained total testosterone, lean mass and strength from training, but boron had no effect on any of them. The authors concluded that bodybuilding raised these measures and boron "affects these variables not at all". The dose was lower than in the 2011 study, so a higher dose could behave differently, but that has not been shown in a controlled trial.
How it is used in studies
Human trials have used about 2.5–10 mg a day for one to seven weeks. Typical diets already supply some boron, especially diets rich in fruit, vegetables and nuts. There is no standard "testosterone dose", and the products sold for this purpose are usually multi-ingredient blends, so any effect cannot be attributed to boron alone.
Side effects, safety and anti-doping
At the doses used in trials, boron appears well tolerated. Much larger amounts are toxic, causing nausea, vomiting, diarrhoea, skin problems and, in animal studies, effects on reproduction and development. Limits differ by region:
- The US Institute of Medicine set a tolerable upper intake level of 20 mg a day for adults.
- EFSA in Europe set a more cautious upper level of 10 mg a day for adults.
These limits include food and supplements together. Stacking several "booster" products can push intake higher than you think.
Boron itself is not banned in sport. The bigger risk is the product it comes in. "Testosterone booster" and muscle-building supplements are among the most frequently contaminated: an international analysis of 634 supplements (Geyer et al., 2004) found 14.8% contained anabolic steroids not declared on the label, and FDA warnings from 2007 to 2016 linked most adulterated muscle-building products to hidden steroids (Tucker et al., 2018). Under WADA's strict liability rule, an athlete is responsible for any banned substance in their sample, whatever the source. If you compete, use only batch-tested products certified by Informed Sport or NSF Certified for Sport.
This page is not medical advice. If you have symptoms of low testosterone (low libido, erectile problems, fatigue, loss of muscle, low mood), see a doctor for a proper blood test rather than self-treating with supplements.
Who might benefit
Possibly no one in the sense the marketing implies. People who eat few fruits and vegetables may have low boron intake, and improving the diet is the sensible fix. Healthy men with normal testosterone should not expect a meaningful change. For strength and muscle, creatine and enough protein have far better evidence, together with strength training.
Bottom line
Boron's reputation rests largely on one week-long study of eight men without a placebo group. A controlled trial in bodybuilders found no effect on testosterone, muscle or strength. Boron does not raise VO2max, and booster products carry a contamination risk. Training, sleep and adequate food remain the real levers; see how to improve VO2max and the other testosterone boosters we have reviewed, such as zinc and tongkat ali.
Frequently asked questions
Does boron increase testosterone?
One small study of eight men found higher free testosterone and lower estradiol after a week of 10 mg a day, but it had no placebo group, and a placebo-controlled trial in bodybuilders found no effect. The evidence is too thin to say it works.
What are the benefits of boron for men?
Boron is a trace element found in fruit, vegetables, nuts and legumes. Claimed benefits for testosterone, muscle and joints rest on very small or short studies, so no benefit for healthy men is proven.
How much boron is safe?
The US upper limit is 20 mg a day for adults and the European limit is 10 mg a day, counting food and supplements together. Most trials used 10 mg or less.
Does boron help endurance or VO2max?
No. There is no study showing boron raises VO2max or endurance performance, and no plausible mechanism for it to do so.
Sources
- Naghii MR, Mofid M, Asgari AR, Hedayati M, Daneshpour MS. 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.
- Green NR, Ferrando AA. Plasma boron and the effects of boron supplementation in males. Environ Health Perspect. 1994;102(Suppl 7):73–77.
- Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academies Press; 2001.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Opinion related to the tolerable upper intake level of boron (sodium borate and boric acid). EFSA Journal. 2004.
- Geyer H, Parr MK, Mareck U, Reinhart U, Schrader Y, Schänzer W. Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study. Int J Sports Med. 2004;25(2):124–129.
- Tucker J, Fischer T, Upjohn L, Mazzera D, Kumar M. Unapproved pharmaceutical ingredients included in dietary supplements associated with US Food and Drug Administration warnings. JAMA Netw Open. 2018;1(6):e183337.