Sex Hormone Binding Globulin

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Summary

  • Introduction.
  • How Insulin May Affect SHBG.
  • How SHBG Affects Free versus Bound Sex Hormones.
  • Impact of Low SHBG.
  • Impact of High SHBG.
  • How to Increase SHBG (When it’s Too Low).
  • How to Reduce SHBG (When it’s Too High).
  • Causes for High SHBG (in Men).
  • Sources.

Introduction

  • Sex hormone binding globulin (SHBG).
  • SHBG is a glycoprotein primarily produced in the liver.
  • Most commonly found in the bloodstream.
  • It binds the sex hormones, including testosterone and estrogen.
    • Transports these hormones throughout the body.
  • Link between insulin / glucose and IGF-1:
    • Glucose drives insulin.
    • Insulin drives SHBG.
    • SHBG drives free testosterone.
    • Free testosterone drives IGF-1.

How Insulin May Affect SHBG

  • Inverse relationship between serum insulin and SHBG
    • Ie, if insulin is low, SHBG is high.
  • Likely that insulin inhibits production of SHBG.
  • In other words, low insulin may negatively influence level of free testosterone.

How SHBG Affects Free versus Bound Sex Hormones

  • Testosterone and sex hormones are referred to as “bound” when attached to SHBG.
  • When these hormones are not bound to SHBG, they are referred to as “free”, or “bioavailable”.
  • Most sex hormones circulating are bound to SHBG.
  • Only 1-2% are free and biologically active.
  • Relative binding affinity:
    • DHT > testosterone > androstenediol > estradiol > estrone

Impact of Low SHBG

  • High levels of (free) sex hormones.
  • Excess growth of cells leading to the formation of certain cancers.
  • Elevated triglycerides and LDL.
  • Linked with cardiovascular illnesses, type 2 diabetes, and high blood pressure.

Impact of High SHBG

  • Decreases the amount of free testosterone.
  • Associated with infertility, a decreased sex drive, and erectile dysfunction.
  • Reduced muscle growth and impaired post-workout recover.
  • Reduce bone mass.

How to Increase SHBG (When it’s Too Low)

  • Reduce calories.
  • Aerobic exercise.

How to Reduce SHBG (When it’s Too High)

  • Conversely, exercise and reduced calories may produce unwanted increase SHBG.
  • Therefore, avoid over-training.

Causes for High SHBG (in Men)

  • Elevated estradiol levels from conversion of testosterone.
  • Extreme weight loss in anorexia nervosa.
  • Certain medications.
  • Liver cirrhosis.
  • Cigarette smoking.
  • Compromised liver detoxification (alcohol abuse, meds, heavy metals etc.)
  • Testicular cancer.

Source

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