Social media widely promotes testosterone as an essential part of menopausal hormone therapy (MHT, also known as hormone replacement therapy or HRT) to treat low mood, brain fog and loss of vitality.

As a result, some women who aren’t prescribed it as part of the MHT regimen feel they’re missing out.

At menopause, when menstruation finally stops, oestrogen levels fall substantially, which can cause symptoms such as hot flushes, night sweats and vaginal dryness. Replacing this oestrogen with MHT relieves these symptoms.

But our new research, recently published in The Lancet journal eBioMedicine, shows testosterone doesn’t change like oestrogen when women reach perimenopause or menopause.

Rather, testosterone declines with age.

We’ve long suspected this – but early tests weren’t reliable

Our 2005 study of 1400 women showed testosterone blood levels did not change at menopause, but gradually declined from the age of about 20.

This followed a smaller study of 172 women in 2000 that found no change in testosterone blood levels at menopause.

But these older studies need to be interpreted with caution. Testosterone was measured with chemical tests that were not able to accurately measure testosterone at low levels in women.

Since then, we’ve used newer, gold-standard methods that can accurately measure small amounts of testosterone.

Using these methods in a 2019 study of 588 women, we found the average decline in testosterone between the ages of 18 to 39 years was about 25%.

Our latest study examined the blood testosterone levels of 1104 participants aged 40 to 69 years. The participants provided extensive menstrual cycle information, so we could determine whether each woman was pre-menopausal, perimenopausal or postmenopausal.

We excluded women taking medications that might impact their natural hormone levels, or who had other identifiable factors that would impact their hormones from our hormone analysis. Having a higher body mass index (BMI) and being a cigarette smoker, for example, are each associated with higher testosterone.

What our new study found

Participants’ testosterone blood levels declined, on average, by 25% between the ages of 40 and 58-59 years.

There were no measurable differences between women who were premenopausal, perimenopausal or postmenopausal.

Postmenopausal women who had both ovaries surgically removed had lower blood testosterone levels than postmenopausal women with at least one ovary. This provides additional evidence that women’s ovaries continue to be the source of some testosterone after menopause.

Read more: I’m a woman approaching middle age – do I need to get my hormones checked?

Interestingly, testosterone blood levels subtly increased from the age of 58 to 59 years. This echoes our 2005 study that found testosterone blood levels bottomed out at about the age of 62 years, and then gradually increased.

All of these findings are changes that occur on average. Not everyone will experience the same changes we observed. Some might experience more or less change with age.

So how does testosterone change over a woman’s lifespan?

Combined with our past studies and other research, our latest study has enabled us to build a picture of testosterone across a woman’s lifespan.

Testosterone levels tend to decrease by about 50% from about age 20 through to about age 60.

Then they begin to subtly increase, with the trend for levels to increase continuing into the eight and ninth decades of life. We are yet to understand why these changes occur.

Read more: Redrawing the map: Why the current menopause criteria may be outdated

Whether low testosterone is associated with symptoms needs further exploration. However, research to date suggests women with low testosterone aren’t more likely to have lower sexual desire, poorer muscle mass or lower mood.

Nonetheless, the gradual increase in testosterone may partly explain the age-related hair thinning and bothersome facial hair growth many women in their 60s and older experienced.

What does this mean for testosterone therapy?

Researchers proposed the idea of a “testosterone deficiency syndrome” in menopausal women more than 20 years ago. This was before testosterone had been measured across women’s lifespans and before robust studies of the relationships between blood testosterone levels and specific symptoms.

Our research refutes the belief that menopause causes testosterone deficiency, and that testosterone supplementation is an essential part of MHT.

Multiple clinical trials have shown testosterone treatment can modestly improve sexual desire in postmenopausal women who have experienced a change in their sexual desire that bothers them.

However, there’s currently no robust or consistent evidence that testosterone therapy will improve any symptoms for women other than low sexual desire after menopause.

Therefore, the international clinical guidelines state it should only be prescribed for low sexual desire in postmenopausal women.

We’re currently evaluating the effects of testosterone on women’s muscle function and bone density and will report these findings in this year.

This article is republished from The Conversation under a Creative Commons licence. Read the original article.