Boron Does Not Lower Free Testosterone—It Increases It
Boron supplementation increases, rather than lowers, free testosterone levels and should not be used if your goal is to reduce free testosterone. 1
Evidence for Boron's Effect on Free Testosterone
Direct Hormonal Effects
Boron supplementation (10 mg daily) significantly increases free testosterone after one week of use, with concurrent decreases in sex hormone binding globulin (SHBG) and estradiol. 1
Within 6 hours of a single 10 mg boron dose, SHBG levels decrease significantly, which mechanistically leads to more unbound (free) testosterone in circulation. 1
The proposed mechanism involves boron disrupting the binding interactions between SHBG and sex hormones, effectively uncoupling testosterone from its carrier protein and increasing the bioavailable fraction. 2
Magnitude and Consistency of Effect
Multiple studies in both humans and animals demonstrate that boron supplementation elevates plasma testosterone and 17β-estradiol concentrations, with the testosterone effect being particularly pronounced in men. 3, 4, 5
In postmenopausal women and older men, 3 mg daily boron supplementation elevated serum concentrations of both 17β-estradiol and testosterone compared to boron-depleted states. 5
Clinical Context for Managing Elevated Free Testosterone
If your actual goal is to lower elevated free testosterone (particularly in the context of low SHBG), the appropriate interventions are:
Primary Management Strategies
Weight loss is the most effective intervention for patients with obesity, as it significantly increases SHBG levels and normalizes free testosterone. 6
Improving insulin sensitivity through diet and exercise addresses the metabolic factors driving low SHBG. 6
Oral estrogens can increase SHBG synthesis in appropriate clinical contexts, thereby reducing free testosterone. 6
Diagnostic Workup
Confirm elevated free testosterone with repeat morning measurements (8-10 AM) to account for diurnal variation. 6
Evaluate underlying causes of low SHBG including obesity, liver disease, hypothyroidism, and medication effects. 7, 6
In men, calculate the free testosterone index (total testosterone/SHBG ratio), where values >0.3 may indicate excess free testosterone. 7
Critical Pitfall to Avoid
Do not use boron supplementation if you are trying to lower free testosterone—this will worsen the hormonal imbalance by further decreasing SHBG and increasing free testosterone levels. 1, 2