One of the factors which causes a decline in free testosterone levels is excessive binding of testosterone to carrier proteins, this divert it’s use in the production of other proteins/hormones, including estrogen.
Aging men sometimes convert testosterone to estrogen. The estrogen is then taken up by testosterone receptor sites in cells throughout the body. When an estrogen molecule occupies a testosterone receptor site on a cell membrane, it blocks the ability of free testosterone to induce a healthy hormonal signal. It does not matter how much serum free testosterone is available if excess estrogen is competing for the same cellular receptor sites.
The most common medical prescription to increase free testosterone is exogenous testosterone replacement. Obviously you should consult with a qualified doctor or endocrinologist about whether that route is appropriate for you at this time.
“Testosterone within the circulation is principally bound to proteins,
the most important of which is sex hormone binding globulin (SHBG).
Only about 2 percent of testosterone is unbound or free testosterone (bio-available) and therefore free to enter cells in order to effect its biological actions by binding to androgen receptors….”
“Hypotestosteronaemia levels [that is, low levels] quoted in papers
vary between around 300 ng/dl (10.4 nmol/L) and 400 ng/dl (13.9
HYPOGONADISM – WHAT IS A LOW LEVEL OF TESTOSTERONE?
“Bioavailable testosterone refers to the ‘free’ testosterone of the hormone unbound to carrier proteins which is able to act directly upon target tissues.”
You can not maintain or build muscle mass without having free/unbound testosterone in your body.
Sexual Dysfunction and Male Hormones
“It is well known that androgen levels decline in men with age.
Furthermore, as a result of the increase in binding capacity for
testosterone in serum, there is an early and more dramatic decline in
free testosterone, the physiologically functioning component of serum
testosterone, than in the total testosterone concentration….”
“The ideal therapy should consist of creating physiologic testosterone
concentrations (400 to 700 ng/dL in blood taken in the morning) and
restoring circadian variations.”
Hormone Replacement Therapy for Aging Men