Andropause
 Normal male aging is accompanied by a decline in testicular function resulting in a fall in serum levels of free testosterone. Around the age of 40 the level of free testosterone begins to decline about 1% a year.
Age related decreasing levels of free testosterone and/or increasing estrogen levels may cause a deficiency known as Andropause or male menopause.
The reasons why free testosterone levels decline with age include:
- A protein called SHBG (Sex hormone binding globulin) rises as we age and more testosterone is bound up to it, reducing the amount of free and available testosterone.
- More testosterone may be converted into estradiol (an estrogen) by an enzyme called aromatase which susequently may then be converted into another estrogen called estrone.
- Estrone is the strongest of all estrogens and tends to accumulate in the body. Increasing estrogen levels negatively feeds back onto the brain slowing down further testosterone production.
- More testosterone may be converted into dihydrotestosterone (DHT) by an enzyme called 5 alpha reductase.
- Less testosterone is made by the aging testicles
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