Oestrogens

The most powerful oestrogen is oestradiol (26). In men this is mainly produced from testosterone by an enzymatic conversion (aromatisation) by the enzyme aromatase (27, 28). Excess oestradiol causes:

Inhibition of testosterone production (29)
Feminine body fat patterning (27)
Gynaecomastia (breast tissue overgrowth) (30)
Increased sex hormone binding globulin (SHBG), a blood borne binding protein which ties up free testosterone, thereby effectively lowering testosterone levels still further (31,32).

Oestrogens are also becoming increasingly heavily implicated in prostate disorders and some now recommend that prostate protection plans should consider oestrogens as well as DHT (33,34,35,36).

Oestrogens are not all bad. In fact, it is through oestrogen that many of testosterone's actions are mediated. Some oestradiol is essential for maintenance of:

Mood (37)
Libido (37, 38 )
Bone mineral density (39,40,41)
Cardiovascular health (42,43,44,45)

Oestrone is another oestrogen found in men (30). It is formed primarily by aromatisation of androstenedione by the enzyme aromatase (28,31). Oestrone is a weaker oestrogen than oestradiol, possessing about 20% of its activity, but it is readily converted into oestradiol (46). Moreover, in aging or obese men oestrone concentrations can be high, so oestrone's impact can itself be significant.

The concept of balance is paramount. The goal is to maintain a healthy testosterone:oestrogen ratio, ideally around 200:1 (47).