Washington: Researchers have claimed that low testosterone production may not be the main culprit in age-associated changes in men and that oestrogen could be at least partially responsible for some of these symptoms.
The study enrolled two groups of men with normal reproductive function, ages 20 to 50, and all participants were first treated with a drug that suppresses normal production of all reproductive hormones.
Men in the first group were randomly assigned to receive daily doses of testosterone gel at one of four dosage levels or a placebo gel for 16 weeks.
Men in the second group received the same testosterone doses along with an aromatase inhibitor which markedly suppressed conversion of testosterone into oestrogen.
Among participants in whom oestrogen production was not blocked, increases in body fat were seen at what would be considered a mild level of testosterone deficiency.
Decreases in lean body mass, the size of the thigh muscle and leg strength did not develop until testosterone levels became quite low.
In terms of sexual function, sexual desire was reported to decrease progressively with each drop in testosterone levels, whereas erectile function was preserved until testosterone levels were extremely low.
In participants also receiving the aromatase inhibitor, increases in body fat were seen at all testosterone dose levels, but suppressing oestrogen production had no effect on lean mass, muscle size or leg strength.
Adverse effects on sexual function were much more obvious when oestrogen synthesis was suppressed regardless of participants' testosterone levels.
The study has been published in the New England Journal of Medicine.