The prostate gland is highly unusual because it undergoes an increase in size at several stages during most of a man's life.
The first growth phase is completed before or at birth, when the average prostate weighs about 1.5 grams.
The second growth phase occurs early during puberty, when the weight of the prostate gland increases to around 11 grams.
The third growth phase occurs during the mid-20s, when the weight of the prostate gland increases to approximately 18 grams.
There is another apparent growth phase that begins when a man is in his 50s.
By the time a man is in his 70s, the prostate gland has reached a maximum weight of 31 grams.
Therefore, throughout a man's lifetime, the prostate gland normally increases in weight about 21 times, compared to its birth weight.
Although the prostate gland grows during much of a man's life, urinary flow problems usually appear only after the age of 50 as a consequence of the final growth phase.
Sex Hormone Changes That Occur With Aging
We do not know why the prostate gland enlarges during multiple growth spurts. However, there are two theories that attempt to explain this phenomenon. Both theories believe hormonal changes over time are responsible.
Changes in the normal balance of sex hormones. With advancing age, the amount of the male hormone testosterone, decreases relative to the amount of circulating estrogen, the main female reproductive hormone which also circulates in the male.
There is some evidence to suggest that this relative increase in circulating estrogen may strengthen the effect of the testosterone derivative DHT, which promotes cell growth in the prostate gland and is formed when testosterone is acted upon by a specific enzyme. As a consequence of estrogen and DHT acting together, cell growth and glandular enlargement are promoted.
Changes in the role of DHT. Prostate gland development requires the conversion of testosterone into DHT (dihydrotestosterone), in the presence of a specific enzyme called 5-alpha reductase. As aging occurs, the amount of DHT in the prostate gland remains high, even through the circulating testosterone level drops.
Some evidence supports the idea that this high level of prostate DHT may by itself promote cell growth and lead to enlargement.