Does HRT prevent osteoporosis? About a quarter fewer fractures

HRT does prevent osteoporosis where it counts, which is broken bones rather than a better scan result. Osteoporosis means bone that has lost enough density and internal structure to break under force that would not normally break it [1][8]. In the Women's Health Initiative, 16,608 postmenopausal women aged 50 to 79 took either oestrogen plus a progestogen, a synthetic version of progesterone included to protect the lining of the womb, or a placebo for an average of 5.2 years. The hormone group had about a third fewer hip fractures and about a quarter fewer fractures overall [13].

A Cochrane review published in 2025 pooled 24 randomised trials of hormone therapy lasting at least a year, covering 45,660 women, with close to 70% of the data coming from the Women's Health Initiative and one other large trial [14]. It found about 22% fewer fractures of all kinds on combined oestrogen and progestogen, and about 27% fewer on oestrogen alone in women who had had a hysterectomy, surgery to remove the womb, both rated moderate certainty, the second-highest confidence grade the review gives [14].

Those percentages sound bigger than the counts behind them. Spread across the trial population, the hormone group had 5 fewer hip fractures and 6 fewer bowel cancers for every 10,000 women each year, against 8 more breast cancers, 8 more strokes, 8 more blood clots in the lung and 7 more heart events over the same period [13]. The trial was stopped in 2002, short of its planned 8.5 years, because the breast cancer count crossed a pre-set safety limit [13].

The two kinds of therapy do not carry the same risks. In the oestrogen-only trial, 10,739 women who had had that surgery were followed for about seven years, and the Cochrane reading of it is that oestrogen on its own probably makes little or no difference to breast cancer risk or to heart events, while probably raising the risk of stroke and of gallbladder disease needing surgery [14].

Osteoporosis guidelines do not put oestrogen first. The North American Menopause Society's 2021 position statement lists it among the therapies available to prevent bone loss in women at high risk, naming perimenopausal women, meaning those in the years around their last period, with low bone density and other risk factors as the clearest candidates, and for women who already have osteoporosis it points to bisphosphonates and newer drug classes instead [12]. Bisphosphonates, a class of tablets and infusions that slow the removal of bone and the most widely used of those options, reduce fracture rates by roughly half [2]. An Endocrine Society guideline makes the same underlying point: several drug classes cut fracture rates at acceptable risk, and the choice should start from a woman's own fracture risk, worked out with a tool calibrated to her country [4].

Bone is rebuilt constantly. Osteoclasts are the cells that dissolve old bone, osteoblasts are the cells that lay down new bone, and in a healthy adult the two roughly balance [2][8]. Oestrogen's job in that cycle is restraint: it holds back the production of osteoclasts, so fewer demolition sites are open at any one time, probably by way of signalling chemicals in the bone marrow called cytokines [7].

When oestrogen falls at menopause, the brake comes off. Removal speeds up and outpaces replacement, and the damage is structural rather than only a matter of quantity. In the spongy bone inside the vertebrae, the internal struts are not merely thinned but drilled through, which wrecks the local architecture and leaves tiny fractures behind; in the dense outer shell of the long bones, loss starts on the inner surface, and the shell itself later turns more porous [7]. Less bone, arranged worse, breaks more easily.

Hormone therapy puts the brake back on. Oestrogen reverses the raised bone turnover that follows menopause and prevents the bone loss that comes with it [3]. That also marks the limit of the approach, because oestrogen deficiency is one cause of fragile bone among several: too little calcium or vitamin D, overactive parathyroid glands, the four small glands in the neck that govern calcium, and how much bone a person built during growth all feed the same outcome [8].

The trials carrying this evidence were not designed around bone, and it shows. The Women's Health Initiative was built to test heart disease prevention, with breast cancer as its main safety outcome, and it ended at an average of 5.2 years rather than the planned 8.5, so nothing in it describes what happens to fracture rates over decades [13].

Who was studied matters too. Most participants were American women over 60 with at least one other health condition, and only about 30% were aged 50 to 59 at the start - the group most likely to be weighing up hormone therapy in the first place [14]. The therapy tested was an oral tablet of conjugated equine oestrogens with medroxyprogesterone acetate, the combined preparation most used in the United States at the time [13], and the Cochrane authors say plainly that these numbers may not describe the patches, gels and other preparations in use now [14].

How long any protection lasts is unsettled. A 1997 review, written before those randomised results arrived, noted that the size of the fracture reduction at the spine, hip and wrist had never been pinned down accurately, and that holding on to maximum protection may require treatment to continue rather than stop [3].

The evidence above does not apply to:

• men, who were in none of these trials
• premenopausal women
• transgender people on gender-affirming hormone therapy, which no trial here tested
• bone loss driven by long-term steroid tablets, which has its own mechanism and its own literature [6]

Hormone therapy is a prescription medicine. Whether the bone benefit is worth what comes with it depends on a person's own fracture risk and medical history, which is a conversation with a doctor rather than something to read off a trial average [4][12].

Hormone optimisation sits on the service list at many longevity clinics, usually beside blood panels and body composition scans. A first visit is normally a medical history, a blood draw to measure hormone levels, and a conversation about symptoms.

Where bone is the actual worry, though, the measurement the guidelines run on is not a hormone level. It is bone mineral density, the amount of mineral packed into a given area of bone, which clinics measure with a DEXA scan, a low-dose X-ray that compares your bones with a young adult average. Density is what identifies who is at risk of fracture and what therapy decisions are monitored against [1], and it is fed into a fracture risk tool calibrated to the country you live in [4]. That way of combining bone density with other risk factors to estimate fracture risk was set out in a 1994 World Health Organization report [5].

So the question worth taking into any clinic that offers hormone therapy for bone is which number is being treated, and what the randomised trials found sitting alongside the fracture reduction [13][14].