M.E SCIENCE
By Josh Hodnik
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Manag tain muscle
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ex hormone binding globulin (SHBG)
is a protein in your body that sex
hormones like testosterone and
estradiol often bind to before entering
your bloodstream. SHBG rarely pops up
in conversation but it plays a major role in how
efficiently hormones are used in the body.
S
HBG is called a glycoprotein
that binds to, transports,
and inhibits the function of
testosterone. It is often thought
that SHBG transports and
protects testosterone from
being eliminated too quickly.
When testosterone is bound
to SHBG, it become useless.
In this state testosterone is
not active or bioavailable.
Testosterone does not normally
break free from SHBG and is
not active when bound. For
this reason SHBG as a protein
cannot be viewed as protecting
and transporting testosterone.
Rather, as a protein, it keeps
hormone levels in balance in
the body.
In the womb low levels of
SHBG are present to allow
activity of sex hormones. This
allows formation of sex organs
when gender is determined.
SHBG levels rise after birth and
remain elevated throughout
childhood. These levels will
drop to half for girls and a
quarter for boys during puberty.
The decrease of SHBG during
pubescent years is caused by
an increase in growth hormone.
Growth hormone levels will
decrease during adulthood and
SHBG will rise. Levels normally
increase at a rate of 1% per year
after early adulthood, resulting
in lowered free-testosterone.
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Muscle Evolution
Add declining total testosterone
levels while we are ageing and
the impact can be significant.
The 1% yearly increase is just
an average, and this can vary
significantly from person to
person. There are many factors
that can influence a rise or fall in
SHBG levels.
Normally 45% of total
testosterone is bound to SHBG,
53% is bound to albumin, and
2% is unbound and active –
referred to as free-testosterone.
Unlike testosterone that is
bound to SHBG, albumin-
bound testosterone can
break free and become free
fairly easily. A bodybuilder
who has normal testosterone
levels and high SHBG levels
can experience the same
symptoms that occur in men
with low-testosterone. Since
testosterone that is bound to
albumin will eventually become
active, free and albumin-bound
testosterone should be taken
into account when evaluating
testosterone levels instead of
total testosterone.
NORMAL
SHBG LEVELS
IN ADULT
MEN (nmol/L)
<20........Low
20-60.. ..Normal
>60........High
“A bodybuilder who has normal
testosterone levels and high SHBG levels
can experience the same symptoms that
occur in men with low-testosterone.”