Alternative names for dihydrotestosterone

DH; 5α-dihydrotestosterone

What is dihydrotestosterone?

Dihydrotestosterone is a hormone that stimulates the development of male characteristics (an androgen). It is made through conversion of the more commonly known androgen, testosterone. Almost 10% of the testosterone produced by an adult each day is converted to dihydrotestosterone. This takes place in the testes and prostate (in men), in the ovaries (in women), as well as the skin and other parts of the body such as the liver. This figure is much lower before puberty however, and it is thought that the increased dihydrotestosterone production may be responsible for the start of puberty in boys, causing development of the genitals (penis, testes and scrotum) and growth of pubic and body hair. This hormone also causes the prostate to grow and is thought to combine with testosterone causing the expression of male sexual behaviour. Dihydrotestosterone is many times more potent than testosterone, and many of the effects that testosterone has in the body only happen after it is converted to dihydrotestosterone.

Much less is known about the importance of dihydrotestosterone in women, but it is known to cause much of the body and pubic hair growth seen in girls after puberty and may help to determine the age at which girls begin puberty.

How is dihydrotestosterone controlled?

The amount of dihydrotestosterone present in the body from day to day depends on the amount of testosterone present. When levels of testosterone increase, more of it is converted to dihydrotestosterone and so levels of dihydrotestosterone also increase as a result.

Control of dihydrotestosterone levels in the body is therefore achieved through control of testosterone production, which is regulated by the hypothalamus and the pituitary gland. In response to decreasing levels of testosterone (and therefore reduced amounts of dihydrotestosterone), the hypothalamus releases gonadotrophin-releasing hormone (GnRH), which travels to the pituitary gland, stimulating it to produce and release luteinising hormone into the bloodstream. Luteinising hormone in the blood then travels to special cells in the testes in men (or ovaries in women) and stimulates them to produce more testosterone. As testosterone in the blood increases, more of it is also converted to dihydrotestosterone, resulting in higher levels of dihydrotestosterone as well.

As blood levels of testosterone and dihydrotestosterone increase, this feeds back to suppress the production of GnRH from the hypothalamus which, in turn, reduces production of luteinising hormone by the pituitary gland. Levels of testosterone (and thus dihydrotestosterone) begin to fall as a result, so negative feedback decreases and the hypothalamus resumes secretion of GnRH.

What happens if I have too much dihydrotestosterone?

Too much dihydrotestosterone, often resulting from excess testosterone production, has variable effects on men and women. It is unlikely that levels of dihydrotestosterone will be raised before the start of puberty. It is also unlikely that adult men with too much dihydrotestosterone would undergo recognisable changes. Women with too much dihydrotestosterone may develop increased body, facial and pubic hair growth (called hirsutism), stopping of menstrual periods (amenorrhoea) and increased acne. Abnormal changes to the genitalia may also occur in women with too much dihydrotestosterone.

What happens if I have too little dihydrotestosterone?

Dihydrotestosterone is thought to have fewer effects in women and, as a result, it is believed they are relatively unaffected by having too little dihydrotestosterone. It is possible, however, that the start of puberty may be delayed in girls with too little dihydrotestosterone and the amount of pubic and body hair present in adult females may also be reduced.

In contrast, low levels of dihydrotestosterone in men can have dramatic effects. If there is too little dihydrotestosterone whilst male foetuses are still in the womb, for example, they may not be 'masculinised' and their genitalia may seem similar to that seen in girls of the same age. Later, boys with too little dihydrotestosterone may undergo some of the changes usually seen in puberty (such as muscle growth and production of sperm) but will not develop normal body hair growth and genital development.