View more posts about this topic:

Gender-Affirming Hormone Therapy and Bone Health

Authors: Katrina Farr-Handley and Dr Ingrid Bretherton.

A man lying on a medical scanning bed, visible in the blurred background. In the foreground, a computer screen displays a scan of his spine. A nurse is looking at the screen. — *A nurse looking at a patient's DEXA scan (izusek, iStock).*

Oestrogen and testosterone are involved in maintaining and facilitating a wide array of systems within our body, including bone health. If you are thinking about starting or already using gender-affirming hormone therapy (GAHT), whether it be feminising or masculinising GAHT, it is important to consider how our bodies may change in ways that may not be at the forefront of our minds or visible to our eyes.

There is a lot of information out there about GAHT, and it can be difficult to know what information is up-to-date and accurate. It is important to be well informed about the effects of GAHT on our bodies, so that we can continue to advocate for ourselves.

To combat mis/disinformation about the impacts of GAHT, this post aims to provide the latest evidence-based information about GAHT and bone health.

What is bone health and how is it measured?

It is widely known that sex hormone levels are an important player in maintaining our bones and their strength.

Bone health is typically measured using Bone Mineral Density (BMD) via dual-energy X-ray absorptiometry (DEXA), which is a measurement of the amount of minerals (typically calcium phosphate) found within a section of bone. When bones grow and develop, specialised cells in the bone deposit a connective tissue web, which is then hardened by calcium phosphate crystals being deposited. This process, called ‘mineralisation’ is very important in providing structural support for the bone and by extension, your body.

When calcium phosphate crystals are not deposited in high enough quantities and rates to match those of bone removal, bones can become weakened and structurally compromised often leading to an increased risk of bone fractures, a condition known as osteoporosis.

Two images displayed side-by-side. On the left, a feminine trans person is wearing a blonde wig, makeup, and a dress. On the right, a masculine trans man is wearing a collared shirt. Both are smiling happily. — *Left: A feminine trans person (Baliente Agency, Unsplash). Right: A trans man (FG Trade, iStock).*

Does taking GAHT impact bone health?

While it is well established that sex hormone levels are important to maintaining bone health in the general population, less is known about what taking oestrogen or testosterone GAHT means for our bones.

Current research is far from conclusive.

Oestrogen/Feminising GAHT

In the case of oestrogen/feminising GAHT, both increases and decreases in BMD have been recorded and there are limitations to the reliability of DEXA to measure bone when large body composition changes are also taking place simultaneously (which occur on GAHT). Specialised high resolution bone CT scanning can measure bones more accurately and showed those on feminising GAHT had lower bone density than cisgender men. One study that looked at risks of fractures found that in comparison to cisgender women, older trans people using oestrogen (>50 years old) had a comparable fracture risk to cisgender women, while younger trans people using oestrogen (<50 years old) had a higher fracture risk to cisgender women, a discrepancy that may be accounted for by other factors affecting BMD (see below).

The effect of progesterone on the BMD of trans people has, unfortunately, not been investigated. However, extrapolating the effects it has on cisgender women, there should not be any detrimental effects on the BMD of trans people using progesterone, in comparison to cisgender women.

Like progesterone, the way anti-androgens (testosterone-blockers) spirolactone and cyproterone acetate affect BMD in isolation in trans people has not been established. While both have been used in studies, they are used only in conjunction with oestrogen. AusPATH National Treatment Guidelines currently has no recommendations for taking either anti-androgen in isolation for the purposes of GAHT.

Testosterone/Masculinising GAHT

The effects of testosterone/masculinising GAHT on the BMD of trans people is, again, inconclusive. Various studies using DEXA indicate either a general increase in BMD or no change at all. A study using specialised high resolution bone CT scanning was reassuring and showed that those on masculinising hormone therapy have higher bone density than cisgender women. A study done on fracture risk indicated that the fracture risk for trans people using testosterone was slightly lower than cisgender men.

A plus size, disabled, Black non-binary person walking with two hiking poles, looking at a sign which reads, "Nature house" and "Trillium trail" with a disabled symbol. — *A non-binary person embarking on a forest hike (Disabled and Here).*

Some things to keep in mind

It is important to keep in mind that, in research that has detected loss of bone with GAHT, some of these studies detect losses in bone mass by comparing an individual’s BMD before and after starting GAHT, with inadequate comparator groups (control groups) or by comparing the BMD of trans individuals using GAHT with cisgender people with the same sex recorded at birth (e.g. cisgender men and trans women), when it would be ideal to compare to both cisgender men and women comparator groups.

Additionally, it is important to understand that hormonal concentrations are not the sole factor that alters a person's bone mineralisation. Other biological and chemical considerations include vitamin D and calcium intake which can be affected by a wide variety of other things, including food intake, exercise, weather, and mental health. If you are worried about GAHT or other factors that might negatively impact your BMD, you should talk to your doctors about ways to monitor and increase your intake of these other important molecules, before altering your GAHT schedule.

There is no research that shows GAHT negatively impacting BMD to the point that the individual would be considered osteoporotic.

Overall, GAHT is safe and effective, and with careful monitoring can be commenced in those at risk of developing bone health issues. For those not at increased risk of bone health issues, routine monitoring similar to the general population is recommended.

Find more information about options for oestrogen, anti-androgens, and progesterone hormone therapy in Australia here.

Find more information about options for testosterone hormone therapy in Australia here.

Wanting to start GAHT but not sure where to start? Find information about accessing GAHT in Australia here.