"When it comes to sex hormones, few things are as misunderstood as the relationship of the prostate to dihydrotestosterone. The inaccurate and overly simplistic attitude that dihydrotestosterone is responsible for prostate hypertrophy, and even prostate cancer predominates amongst most people.
The real situation is, of course, much more complex. One must understand that there are marked differences between healthy prostate growth (developmental growth), prostate growth due to BPH, and cancerous prostate growth.
The first period of prostate growth, deemed developmental growth, is connected to puberty and the testicular secretion of androgens. This takes the prostate from its prepubertal dormancy to the normal sized, healthy, and functional prostate gland of an adult. During the early and mid adult years the prostate stays at this stage, despite the constant high levels of androgens in the body. However, if androgens are blocked in the body then the adult prostate will shrink in size. This can occur by castration, or even by blockade of 5-AR (recall that dihydrotestosterone is the active androgen in the prostate).
Later in life, there is often a second stage of growth. This growth is deemed benign prostate hypertrophy (BPH) and this growth occurs in a wholly different hormonal environment than that of developmental growth. Evidence is mounting that the existence of a high estrogen / androgen ratio – a condition common in older men – is highly correlated to the development of BPH.
Experimental studies have shown the inability of androgens with saturated A rings (dihydrotestosterone related) to induce an initial condition of prostate hypertrophy. These compounds are non-aromatizable. Aromatizable androgens on the other hand, such as testosterone or androstenedione can induce hyperplasic modifications of the prostate of monkeys, but these effects are reversed by the addition of an aromatase inhibitor.
So apparently, estrogen is a causative factor in BPH or, probably more accurately, estrogen in the presence of a minimum, permissive amount of androgen."
Patrick Arnold