Sex Hormone Binding Globulin

When SHBG is too LOW (<10 nmol/L):

• Common on oral AAS (Anavar, Winstrol, Proviron, Dianabol suppress SHBG by 50-90%)
• Implications: rapid testosterone clearance, higher free androgen exposure, more androgenic side effects (acne, hair loss, prostate stimulation), unstable hormone levels between injections
• Recovery: SHBG typically normalises 4-8 weeks after stopping oral AAS
• Tamoxifen -- 10-20mg/day (SERMs raise SHBG via estrogenic hepatic action)
• Increase dietary fibre and reduce refined carbohydrates (insulin resistance lowers SHBG)
• Moderate alcohol consumption raises SHBG (not a recommendation to drink, but explains the mechanism)
• Thyroid optimisation -- hypothyroidism lowers SHBG; ensure TSH/Free T4 are optimal

When SHBG is too HIGH (>50 nmol/L off-cycle):

• Implications: more testosterone bound, less bioavailable free T, potential hypogonadal symptoms despite normal total T
• Common causes: ageing, liver disease, hyperthyroidism, low caloric intake, certain medications
• Boron -- 10mg/day (most evidence-supported supplement; lowers SHBG by ~10% within 1 week)
• Stinging Nettle Root -- 300-600mg/day (may compete with SHBG for hormone binding)
• Magnesium -- 400mg/day (deficiency is associated with higher SHBG)
• Vitamin D3 -- 5000 IU/day (deficiency associated with elevated SHBG)
• Address caloric deficit if dieting -- chronic restriction raises SHBG
• Ensure adequate carbohydrate intake -- very low-carb diets can raise SHBG
• Check thyroid function -- hyperthyroidism elevates SHBG significantly

Clinical context:

• SHBG is produced by the liver and regulated by insulin, thyroid hormones, estrogens, and androgens
• Always interpret total testosterone alongside SHBG and free testosterone
• On TRT/AAS: SHBG is less clinically relevant since exogenous hormones flood the system regardless of binding capacity

References:

• Naghii, M. R., Mofid, M., Asgari, A. R., Hedayati, M., & Daneshpour, M.-S. (2011). Comparative effects of daily and weekly boron supplementation on plasma steroid hormones. Journal of Trace Elements in Medicine and Biology, 25(1), 54-58. DOI: 10.1016/j.jtemb.2010.10.001
• Veronese, N., Demurtas, J., Pesolillo, G., et al. (2020). Magnesium and health outcomes: An umbrella review. European Journal of Nutrition, 59(1), 263-272. DOI: 10.1007/s00394-019-01905-w
• Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266-281. DOI: 10.1056/NEJMra070553