Boron and the Liver and Kidneys: Is It Safe

Boron is popular among men as a «natural testosterone booster» and among women as a trace element for bones. However, it is a substance with a fairly narrow gap between a beneficial and an excessive dose, and the main organ that works with it is the kidneys. The editorial team examined how safe boron supplements are for the liver and kidneys.

Boron in the body: where it comes from and where it goes

Boron is a trace element that a person obtains primarily from plant food: fruits, nuts, legumes, avocado, wine, and coffee. In food and in the body it exists mainly in the form of boric acid, which dissolves well in water and is almost completely absorbed from the intestine.

A key feature of boron is that it is practically not metabolized. The liver does not transform it or «neutralize» it, and the body has no mechanism for accumulating significant reserves in soft tissues. Some boron is deposited in the bones, but most is quickly excreted.

The main route of excretion is the kidneys: according to a review by Nielsen (2014), the vast majority of ingested boron leaves in the urine within a day or two. So for boron the kidneys are not only a potential target but, above all, the organ whose function determines whether an excess will accumulate.

Boron is still not officially recognized as an essential nutrient for humans, so there is no recommended daily allowance. Instead, tolerable upper intake levels have been established, which are discussed below.

For the liver, boron is not a typical hepatotoxin: in the clinical literature, liver injury from boron is described mainly in the context of acute boric acid poisoning, rather than the intake of supplements in ordinary doses.

Upper limits: what the regulators say

The American Institute of Medicine (IOM) in 2001 set the tolerable upper intake level (UL) of boron for adults at 20 mg per day. The European Food Safety Authority (EFSA) in 2004 defined a stricter UL - 10 mg per day for adults.

Both figures are derived primarily from studies of reproductive and embryonic toxicity in animals using safety factors. In other words, the upper levels are not a threshold beyond which harm occurs immediately, but a limit below which the risk is considered minimal for most people.

Typical boron intake from food is approximately 1-3 mg per day, and in people who eat a lot of fruits and nuts it can be higher. Most supplements contain 3-10 mg of boron per serving, so total intake can easily approach the European limit.

In human studies where boron was given as a supplement, doses of 3-10 mg per day for several weeks were most often used. For example, in the work of Naghii and colleagues (2011), healthy men received 10 mg of boron daily for a week; no serious side effects in the short term were described.

There are few long-term controlled data on taking boron in doses close to the upper limit, so the editorial team advises not exceeding the recommended levels.

Boron and the kidneys: when a risk appears

Since boron is excreted almost exclusively in the urine, with normal kidney function its concentration in the blood drops quickly after taking a supplement. So in a healthy person, moderate doses do not create the conditions for accumulation.

It is different in people with chronic kidney disease. With a decrease in GFR, the excretion of boron slows down, and the same daily intake leads to higher blood concentrations. There are practically no controlled studies of boron intake by patients with CKD, so it is impossible to assess a safe dose for them.

A direct toxic effect on the kidneys is described in acute boric acid poisoning: in severe cases, acute kidney injury, vomiting, diarrhea, characteristic skin flushing, and seizures are observed. Such conditions are associated with doses orders of magnitude higher than in supplements, and usually arise from accidental ingestion of antiseptics or insecticides.

For an athlete who takes boron within 3-6 mg per day and has normal test results, the risk to the kidneys is considered low. However, the point of «overloading» the body with boron for a hormonal effect is dubious, since the evidence of an effect on testosterone is limited.

Boron and the liver: what is known

The liver does not metabolize boron, so the classic mechanism of drug-induced liver injury (the formation of reactive metabolites) does not exist for it. In hepatotoxicity databases, boron is not listed among the common causes of liver injury from supplements.

However, it is worth considering combination products. Boron is often part of «testosterone complexes» together with tongkat ali, fadogia, tribulus, and other plant extracts. According to a review by Navarro and colleagues (2017), multi-ingredient plant supplements are precisely one of the notable causes of liver injury from supplements.

So if ALT or AST rise while on such a complex, boron is usually not the main «suspect», but you should stop the entire product, not a single ingredient.

In cirrhosis and other severe liver diseases, kidney function is often impaired as well. In such a condition, it is advisable to coordinate any trace-element supplements beyond the usual diet with a doctor.

• healthy kidneys and liver - doses within 3-10 mg/day are considered low-risk;
• chronic kidney disease - intake only with a nephrologist's approval;
• pregnancy - do not exceed the UL, a doctor's consultation is mandatory;
• complexes with plant extracts - assess the risk of each component.

Practical recommendations

Before buying boron, assess your own diet: people who regularly eat fruits, nuts, and legumes already get a significant part of the upper limit. A supplement in that case may be unnecessary.

Choose products with a clearly stated amount of elemental boron (not just the mass of the compound, for example boron glycinate or citrate). Check whether boron is present in your multivitamins and other complexes to avoid duplication.

If you take boron for a long time, basic kidney monitoring - creatinine with a GFR calculation and a general urinalysis - will help ensure that the excretion mechanism is working normally. For the liver, standard ALT, AST, and GGT are sufficient, especially when taking combination complexes.

Nausea, diarrhea, a rash, or unusual skin flushing while taking it is a reason to stop the supplement. Accidental ingestion of boric acid or preparations containing it (especially by children) requires immediate medical attention.

Editorial conclusions

Boron is not metabolized by the liver and is excreted by the kidneys, so for a healthy person, at doses that do not exceed the upper limits (10 mg/day per EFSA, 20 mg/day per IOM), the risk to both organs is low.

The main risk group is people with chronic kidney disease, in whom boron is excreted more slowly and a safe dose has not been established. Injury to the kidneys and liver is described primarily in acute boric acid poisoning, not with the intake of supplements.

A rational approach is to take dietary boron into account, not to duplicate it across several products, and not to count on a pronounced hormonal effect, for which there is still little evidence.

We also recommend reading our materials on boron and testosterone, on tongkat ali and liver safety, and on zinc for athletes.

References

1. Nielsen FH. Update on human health effects of boron. J Trace Elem Med Biol. 2014;28(4):383–387.
2. Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academies Press; 2001.
3. EFSA Panel on Dietetic Products, Nutrition and Allergies. Opinion related to the tolerable upper intake level of boron (sodium borate and boric acid). EFSA J. 2004;80:1–22.
4. Pizzorno L. Nothing boring about boron. Integr Med (Encinitas). 2015;14(4):35–48.
5. 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.
6. Navarro VJ, Khan I, Björnsson E, et al. Liver injury from herbal and dietary supplements. Hepatology. 2017;65(1):363–373.