Testosterone is one of a family of hormones called androgens. Best known for their masculinising effects, androgens first kick into action during the embryonic stages of life. To explain, let's go back to the prudish basics of reproduction biology. An embryo is conceived when a female egg is fertilised with a male sperm. The egg and sperm each donate a single sex chromosome to the embryo, an X chromosome from women, and an X or Y chromosome from men.
If the combination of these sex chromosomes is XX, then the embryo will be female. If it's XY, the embryo will be male. Though in fact, it's not until the sixth week of development that XX or XY embryos are anatomically defined. Before this the human foetus is essentially sexless, possessing a set of "indifferent" genitalia. One interpretation of this is that all embryos begin as female. Testosterone makes the difference, influencing the growth of male genitalia, while the female component of the indifferent genitalia degenerates. But is it only the absence of foetal testosterone that causes an embryo to develop in a female direction? It's a question that we know less about.
According to some, the intimate association between testosterone and male identity starts this early. Anne Fausto-Sterling , in her book, Myths of Gender, believes this inference that "testosterone equals male", while "absence of testosterone equals female", is well-entrenched in the layers of our culture as a notion of "female as lack", and that "such rock-bottom cultural ideas can intrude unnoticed even into the scientist's laboratory".
A girl's hormone too
Testosterone is also well known for its role in the hormonal hotbed that is male puberty. It promotes the growth of the reproductive tract, increases in the length and diameter of the penis, development of the prostate and scrotum, and the sprouting of pubic and facial hair. As well as these androgenic, or masculinising effects, testosterone also drives anabolic, or tissue-building, changes. These include thickening of the vocal chords, growth spurts, development of sexual libido, and an increase in strength and muscle bulk.
There's no denying these powerful physical effects which continue well into adulthood, and their driving force, hormones. But we feel compelled to box our hormones resolutely into those that belong to men, or to women. Estrogen and progesterone are the so-called female sex hormones, and testosterone, the so-called primary male sex hormone. With that we assign our hormones impossible gender roles. But of course gender ain't that simple, and nor are our hormones.
It turns out men and women produce exactly the same hormones, only in different amounts. Men's bodies generate more than twenty times more testosterone than women, an average of seven milligrams per day. Women, via mainly their ovaries and adrenal glands, make a tiny three tenths of one milligram of testosterone per day (1). But it may come as a surprise to know that women's ovaries primarily produce testosterone, from which estrogen is then made. This ovarian production accounts for one-quarter of the total circulating testosterone in a woman's body. Conversely, men's bodies produce their own all-womanly estrogen, converted by their tissues from their all-manly testosterone.
Psychiatrist Dr Susan Rako, believes testosterone is as much a woman's sex hormone as it is a man's. She argues that the "amount of testosterone, tiny as it is, that a woman's body is continually producing is an essential amount." Rako's book, provocatively titled, The Hormone of Desire, is one of a growing wave of publications about the importance of androgens like testosterone to women's health. In calling it the hormone of desire, Rako maintains "testosterone is the hormone most critically implicated in the maintenance of libido, or sexual desire, in women just as it is men".
Its major job starts, as with boys, at puberty. Think of short-and-curlies, hairy armpits, sprouting breasts, and angst about acne. Testosterone is a culprit. But we sure miss it when it's not around.
for many women there's the fear of side effects...
will I grow a beard?
As women age, their levels of circulating testosterone gradually decline. The effect can be especially felt in women around their menopause, when they also experience a precipitous drop in estrogen, or if their ovaries are removed, which prematurely induces a 'surgical menopause'. Rako says the symptoms of a "deficiency" or loss of testosterone can include a loss of vital energy and feeling of "well-being", a loss of familiar levels of sexual libido, sensitivity of nipples and genitals, and a thinning of pubic hair. Other impacts may include a "flatness" of mood, dry skin, brittle scalp hair, and loss of muscle tone and strength. It's understood that testosterone also contributes to the health of a woman's vulva, regrows the vital tissue of the ****oris, and can play a role in curbing osteoporosis by helping maintain the density of our bones. And if that wasn't enough, it can influence our cognitive function as well.
It's an impressive compendium of symptoms, supported by an emerging body of scientific research (based on clinical trials of postmenopausal women). Not all women experience these effects. But for those who do, the option for testosterone replacement therapy is available, for both women and men. There's the choice of patches, pills or implants - each with their own risks and benefits.
For many women there's the fear of side effects. Will I grow a beard? Will I sprout pimples? Will I become as randy as a rooster? Will I bulk-up with big boy muscles? Rako believes the resistance to prescribing supplementary testosterone for a woman with symptoms of deficiency "boils down to a rigid holding to the irrational notion that testosterone for women is unnatural".
Dr Susan Davis, Director of Research of the Jean Hailes Foundation in Melbourne, is one of a small group of scientists worldwide conducting clinical trials into androgen therapy in women. She says the aim is to keep the levels of testosterone within the normal blood level range for a younger woman. The idea is not to make women super-sexual, but to tailor the therapy to individual needs.
As with standard hormone replacement therapy (HRT) for menopausal women, testosterone is not without its strong critics. Unlike HRT, which combines progesterone and estrogen, the research into the side effects of testosterone therapy is relatively young. And should women expect the sexual vibrancy of their youth to last forever? Debates aside, one wonders why we hear so much about progesterone and estrogen in women, but very little about the oh-so-sexy testosterone?
Davis says we have a tendency to accept that men can be sexually active well into their 60s, 70s and 80s. But older women are rarely thought of as sexual, or supported in maintaining their sexual libido. Some say it's a tradition entrenched in an unsympathetic medical profession.
So is testosterone the solution for all women who want saucier sex-lives? Is our libido only titillated by testosterone? Of course our sexuality and libido are affected by much more than our biology. Let's not forget stress, boredom, anxiety, disinterest and exhaustion. But Rako argues "the wipeout of sexual desire that results from a critical reduction in testosterone is different from the fluctuations we experience with the various ups and downs of life and relationships."
Mirror, Mirror on the Wall, Who's the Most Aggressive of Them All?
Boys will be boys. You could cut a knife through the air the testosterone levels were so high. The 'roids were raging, goin' off, peaking, on a roll, out of control, over the top? mighty big men with mighty big hormones, hard yacka and all that...
It's not surprising that our levels of testosterone are understood to affect our behaviour. Testosterone receptors are found in our brain, which means the hormone interacts and binds with our neurons, relaying to them important messages for action. Deborah Blum, author of Sex on the Brain, says this indicates the brain is "prepared to listen to what testosterone has to say" and that "most researchers consider this at least indirect evidence that testosterone is capable of altering the brain, and thus, influencing our behaviour."
