Average SHBG in men aged 30–45 (nmol/L)
Overview
Sex hormone-binding globulin (SHBG) binds tightly to testosterone, rendering it unable to enter cells or activate androgen receptors. High SHBG creates a medically deceptive picture: total testosterone appears normal on a standard blood test, but free testosterone — the biologically active fraction — is critically low. This is extremely common in men on low-calorie diets, with thyroid disorders, elevated oestrogen, or simply ageing. It is one of the most frequently missed causes of testosterone deficiency.
How It Affects Fertility
- Dramatically reduced free testosterone despite normal total testosterone
- Impaired androgenic signalling throughout the reproductive system
- Reduced stimulation of testicular Sertoli and Leydig cells
- All downstream effects of testosterone deficiency despite "normal" lab results
Symptoms to Watch For
- Classic testosterone deficiency symptoms despite being told "your levels are fine"
- Low libido and energy with adequate total testosterone
- Doctors dismissing genuine symptoms based on incomplete testing
What You Can Do
- 1 Always request free testosterone and SHBG alongside total — standard panels miss this entirely
- 2 SHBG rises with: caloric restriction, thyroid dysfunction, liver issues, high oestrogen, ageing
- 3 Boron supplementation (3–10mg/day) has RCT evidence for meaningfully reducing SHBG
- 4 Resistance training reduces SHBG acutely; a sustained programme lowers baseline over time
- 5 Optimise thyroid, reduce alcohol, and ensure adequate dietary fat
This content is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making health decisions.