This is why men with diabetes and heart-disease have lower SHBG and higher estradiol [1-3].
Any activity that increases insulin-sensitivity and lowers free-IGF-1, would therefore increase both SHBG and testosterone and decrease estradiol levels. ...
As I have posted earlier... SHBG does increase with age, but this is not a bad thing; it's what’s suppose to happen. Men with metabolic-syndrome actually have depressed SHBG as they age and their SHBG doesn't rise to its full potential.
In my opinion you are still confusing two distinct issues. I don't disagree that
low SHBG is associated with disease states. So it is good for aging men to have levels higher
than the very low levels associated with these disease states. That does not mean
elevated SHBG in aging men is a good thing. There are aging men who don't have diabetes or heart disease. In fact, they are a majority. As with all blood parameters, there seems to be an optimal window for SHBG, and you don't want to be below
or above that, and most otherwise healthy older men are above that window. If some is good, that doesn't mean that the more the better.
What you basically seem to be saying is that an aging hormone profile is healthier for an older man than a youthful hormone profile, and by implication that a youthful hormone profile is associated with heart disease or diabetes. There is no evidence for that AFAIK.
Actually, SHBG is mainly influenced by fasting-insulin and free-IGF-1 (insulin-like-growth-factor-1).
I was responding to your earlier statement implying that increasing testosterone levels caused SHBG to increase by pointing out that of the sex hormones, it is E2 that drives SHBG up, and that raising testosterone will actually drive SHBG
downwards.
As for the effect of insulin and IGF-1, you may be correct in the presence of the above mentioned disease states where SHBG is abnormally low, but how would you reconcile your statement with the fact that in most otherwise healthy men, SHBG rises with age?
With higher SHBG actually comes less estradiol, because with higher SHBG, less testosterone is up for conversion (into estradiol).
No. As has been pointed out by various posters, since it is mostly free (or more accurately, non-SHBG-bound) testosterone that is converted to E2, and since free testosterone is essentially independent of SHBG, higher SHBG does not translate into less estradiol. In fact, the way the HPT axis regulates hormone levels is via a feedback loop that uses estrogen levels as the main gauge, so it is in fact set up to keep
estrogen levels the same independent of what T or SHBG levels may be.
Edited by viveutvivas, 15 July 2012 - 04:40 PM.