Women's Health Initiative
Also called: WHI study
What it means
The Women's Health Initiative, or WHI, was a major 2002 study on hormone therapy in postmenopausal women that found real but often misreported risks, alongside a clear reduction in fractures.
This study is one of the clearest pieces of evidence that hormone therapy can meaningfully protect bone, including the hip, which matters as you think through your own bone health options with your doctor.
The Women's Health Initiative, often called WHI, was a large randomised trial that gave postmenopausal women either estrogen plus a progestin or estrogen alone, to see how hormone therapy affected their health. It was stopped early in 2002 after researchers reported that combined hormone therapy raised the risk of breast cancer and heart disease. News of this spread fast, and prescriptions for hormone therapy dropped sharply worldwide.
Looking closer at the numbers tells a more nuanced story. The actual increase in breast cancer cases in the combined-therapy group was small in absolute terms, even though it was reported mainly as a relative risk, which sounds much bigger than it is. Women who took estrogen alone, after having a hysterectomy, did not show an increase in breast cancer, and over longer follow-up actually showed a reduction. It also mattered that the average participant was 63, over a decade past menopause.
The one result that has never been disputed is that both forms of hormone therapy significantly reduced fractures, including hip fractures, even in women who weren't selected for having osteoporosis. This makes the Women's Health Initiative an important reference point for understanding how estrogen affects bone, though any decision about starting or stopping hormone therapy belongs with your prescriber, who can weigh your personal health history.
How sure is this?
Graded Strong Clinical Evidence: Supported by multiple well-designed clinical studies in humans. Read each study with its grade in mind. One study is a piece of the picture, not the whole of it.
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Questions people ask about this
Whether hormone therapy is right for your bones is a decision only you and your prescriber can make, based on your personal history — but it's worth knowing the evidence on hormones and bone is actually strong and has often been misrepresented, which is likely why your doctor is being careful. The caution usually traces back to one 2002 trial that was widely misreported; since then, the understanding has shifted considerably, especially around a woman's age and timing when therapy starts.
Read the full answer →Related words
Hormone replacement therapy (HRT) replaces oestrogen, often with a progestin, after menopause and has been shown to…
Estrogen is a hormone that protects bone by keeping bone-removing cells in check. Falling estrogen, especially at…
Menopause is when your periods stop and estrogen levels drop sharply, which speeds up bone loss because the cells…
The timing hypothesis is the idea that when a woman starts hormone therapy, relative to her menopause, strongly…
A hip fracture is a break at the femoral neck, the narrow part of bone connecting the hip joint ball to the thigh…
A fragility fracture is a broken bone caused by a fall or bump that normally wouldn't break a healthy bone, often at…
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
