Why does age make HRT less effective?

[Soapyshoe]

Hey everybody, I've got 2 questions:
1. Why does age make HRT less effective?
2. How much "male" muscle mass can I expect to lose?

Details:
I'm turning 26 soon and it's been well substantiated that HRT becomes less effective the older you are.

My question is simply: Why?  Is it because there's less HGH as you age?  Is it because bones are less likely to grow at an older age?  Is it because there is irreversible soft tissue formation that HRT cannot undo?  It is partly psychological?  Does it have to do with your metabolism?  Is it dietary?  Are there other hormonal processes that just fall off with age, such as the pineal gland shrinking? 

And is there anything behavioral that one can do to increase the effectiveness of hormones?  It stands to reason that diet and exercise would increase your health, which in turn would lead to a more appropriate hormonal balance.  But I haven't read any research otherwise.

Genetically speaking, the women in my family have very full and round cheeks, medium softness skin (not totally soft/supple), an average of a D cup, and tend to be somewhat shorter and thick/muscly for women (not dainty/thin).  I'm the thinnest person in my entire extended family, and aside from testosterone-driven bone and muscle changes, I have the most femenine bodily features (small waist, small wrists, heart-shaped face) out of all the women (but I'm genetically male).  The women also tend to be overweight, but that's mostly due to McDonalds (my grandmothers were both healthy and thin).

I'd be okay if I came out tomboyish after transition, as I'd still be the most girly girl in my family.  I just need to create a REALISTIC set of expectations for what to expect from HRT at my age.

My biggest fear is that I won't lose any muscle mass while on hormones.  My trapezius muscles tall (http://en.wikipedia.org/wiki/Trapezius), and my pecs are just a tad too large.  Nothing on my body is "cut" and I failed to gain muscle mass or definition from serious weight lifting.  I'm currently 6'0", 175lbs, 25 years old .  Up until college, I weighed around 155, and everybody thought I was anorexic.  I'm thinking of dropping 20 lbs in the next 4 months in order to get back to my ideal body weight.  Still, I would like for the "guy" muscle to drop off a bit, but I don't know whether to realistically expect it.

[Nero]

i think it's because the body continues to masculinize. so the less masculinization time ie younger, the better.

[SisterGirlfriend]

i think it's because the body continues to masculinize. so the less masculinization time ie younger, the better.

I believe this is it. Testosterone continues to masculinize the body throughout the lifespan, and does so considerably after about the mid-20s I believe. HGH also plays a role in it. The youthful body is designed to be pliable, so it's quite easy to get a large amount of benefits. 25 isn't really outside the range for a great response to hormones.

[Ms.Behavin]

Hum.. It really depends on genetics.  Bone structure stops growing by about 18-20, Once the soft bone tissue hardens thats about it.  That in my mind means brow ridges etc, too.  Now as one ages the skin gets thinner and that can cause the brow to look heavier, but it's really a soft tissue issue.  HRT on MtF  cause some softening of the facial soft tissue, loss of muscle mass, increased fat deposits, etc.  Plus there is the whole mental change issues which also differs from person to person

Someone in their mid twenties will respond faster then someone in their 40's but it really depends on how you picked your parents.  he mid 20's is still earily enough to have a generally good results.

Beni   

[Nicky]

I really don't think it is that conclusive that the older you are the less effective it is. Certainly if you are still going through puperty then it is going to make a huge difference. But I think from then on it is almost much the muchness. Some people get an awsome result, some don't and that does not seem to be dependent on age. Sometimes how good you think your results are simply depends on your attitude.

You can expect your guy muscles to drop off over time with HRT. This is a realistic expectation. With a lack of testosterone your muscle mass becomes far harder to maintain. It is likely you will lose a bunch unless you actively work at it.

This might be useful: http://en.wikipedia.org/wiki/Hormone_replacement_therapy_(male-to-female)
or https://www.susans.org/wiki/Hormone_replacement_therapy_%28male-to-female%29