Causes & risk factors

Menopause & estrogen loss

Estrogen restrains the bone-resorbing osteoclast. As long as estrogen is present, it holds resorption in check and keeps remodeling balanced. When estrogen falls at menopause, that brake comes off: resorption accelerates, formation can't keep pace, and bone is lost rapidly — a study estimated women lose bone about 6× faster during the menopausal transition than in the 25 years before it. This is why postmenopausal osteoporosis is the most common form of the disease and why women reach a lower peak bone mass and carry a higher lifetime fracture risk than men.

The loss is fastest in the first several years around the final period, then continues more slowly. This early, rapid phase is part of why bone health deserves attention at menopause, not decades later after a fracture. (For hormone therapy's role, see Treatment; for the wider hormonal picture, our sister site MenoExperts covers menopause in depth.)

Aging & bone loss

Independent of menopause, bone is lost with age in both sexes. Remodeling becomes less efficient, osteoblast function declines, calcium absorption falls, vitamin D status often drops, and falls become more likely. The result is a steady rise in fracture risk: after age 50, the risk of an osteoporotic fracture roughly doubles every 7 to 8 years. Low body weight (a low BMI) is one of the most consistent predictors of fracture across all ages.

Osteoporosis in men

Osteoporosis is not only a women's disease. Up to 1 in 4 men over 50 will break a bone because of it. In men, sex-hormone decline is more gradual — and, notably, falling estradiol (produced in men from testosterone) correlates with bone loss even more strongly than falling testosterone itself. Fragility fractures climb in men about a decade later than in women, but their consequences are at least as serious.

The bigger problem is neglect. Men are screened for osteoporosis far less often, are less likely to be tested even after a hip fracture, and are less likely to be treated afterward. In one comparison, osteoporosis screening after hip fracture occurred in about 12% of women but only 5% of men. A fragility fracture in a man deserves the same urgent evaluation it would prompt in a woman. (For low testosterone specifically, see our sister site TestoExperts.)

Secondary causes & medications

A substantial share of osteoporosis is secondary — caused or worsened by another condition or a medication rather than by menopause and aging alone. Identifying these matters, because treating the underlying cause is part of the fix, and because unexplained or unusually severe bone loss should trigger a workup.

Glucocorticoid-induced osteoporosis

Steroids (glucocorticoids such as prednisone) are the most common medication cause of osteoporosis — and one of the most under-treated. Fractures occur in roughly 30–50% of people on long-term oral glucocorticoids. The damage is fast and front-loaded: bone loss is most rapid in the first few months of therapy, because steroids both suppress bone formation (they shorten osteoblast and osteocyte lifespan) and, early on, increase resorption.

Two features make steroid-related bone loss especially dangerous. First, it preferentially weakens cortical bone and raises fracture risk beyond what density alone shows — fractures happen at higher (less abnormal) T-scores than the usual −2.5 threshold, so a "not-quite-osteoporosis" DXA is falsely reassuring. Second, risk tracks dose and duration, but susceptibility varies between individuals. FRAX can be adjusted for glucocorticoid dose to avoid underestimating risk.

Management: calcium and vitamin D for everyone on glucocorticoids, use the lowest effective steroid dose for the shortest time, and add a bone-protecting drug in those at risk. Bisphosphonates are first-line and most widely used; denosumab and the anabolic teriparatide are effective alternatives, and anabolic therapy is reasonable for the highest-risk patients. Encouragingly, some of the bone loss is partly reversible once glucocorticoids are stopped (see Treatment).

Post-transplant osteoporosis

Organ transplantation saves lives — and it is hard on bone. People awaiting a transplant often already have low bone mass from their end-stage organ disease, and then the medications that prevent rejection accelerate bone loss: glucocorticoids plus immunosuppressants (such as calcineurin inhibitors). Bone loss and fracture risk are highest in the first 6–12 months after transplant, and they differ by organ type.

This matters because a post-transplant fracture is an independent predictor of death in these patients, and bone mass often stays below normal long-term. Two strategies help: optimize bone before transplant where possible, and start protection early afterward — calcium and vitamin D, the lowest feasible steroid dose, and an antiresorptive (bisphosphonate or denosumab) or, in selected high-risk patients, an anabolic agent. Anyone who has had, or is listed for, a solid-organ or bone-marrow transplant should have their bone health assessed deliberately rather than left to chance.