American Scientist

To the Editors:

I recently read the article "Estrogen in Men" in the November–December issue by Erik Wibowo and Richard Wassersug. The subject appealed to me immediately, although I was left with a few unanswered questions at the end.

I never knew that men had estrogen, let alone considered the role it had in the male body. As interesting as this subject was, the article left me curious about the role of testosterone in females.

The authors state that it is the enzyme aromatase that transforms testosterone into estradiol. I’m curious to know whether females also have a type of enzyme that would convert estradiol into testosterone, or is it naturally produced in their tissues? I’m also curious to know how much levels of testosterone and estrogen need to decrease or increase in order to cause side effects. What are the ways that the body tries to cope with decreasing or increasing levels of these hormones?

I congratulate Drs. Wibowo and Wassersug on writing an intriguing article and also on making the article easy to understand for people, like myself, who don’t have a background in biochemistry or endocrinology.

Anne-Marie Fortin
Ottawa, Ontario, Canada

Drs. Wibowo and Wassersug respond:

We thank Ms. Fortin for her kind comments. To answer her first question, testosterone is indeed present in women, produced primarily in their ovaries and adrenal glands. Although testosterone can be converted to estradiol, the reverse does not happen. Testosterone, however, is not the main androgen (hormones that promote male characteristics) in women. Instead, dehydroepiandrosterone-sulfate (DHEA-S), dehydroepiandrosterone (DHEA), and androstenedione are the more common androgens in women. These three compounds may then be converted to testosterone to produce masculinizing effects.

Endogenous androgens have normal roles in female biology. For example, they promote pubic and axillary hair growth. A growing body of literature on effects of hormones in women and female-to-male transsexuals indicates that testosterone therapy can enhance to some extent aspects of sexual function (for example, libido and vaginal lubrication), improve memory, strengthen bone, reduce fat mass, and increase lean body mass. However, as noted in our American Scientist article, some of these effects may be due to estrogen produced by the aromatization of their testosterone. The extent to which testosterone affects women’s sexual desire is not fully understood, as S. Wahlin-Jacobsen and colleagues discussed in a 2014 article in the Journal of Sexual Medicine.

Ms. Fortin’s last question relates to how much change in testosterone or estrogen is needed to cause side effects. Various factors (for example, dose, duration, and individual differences) determine whether one may experience side effects from any hormonal treatment. As noted above, low-dose testosterone treatment may help raise libido for some women, but it can also cause facial hair to grow. In contrast, when testosterone is administered at constantly high doses (equivalent to male levels), it can have major masculinizing effects: It can lead to baldness, can cause the pitch of one’s voice to deepen, and may increase the risk of cardiovascular diseases—all features of males.