Glucocorticoids, the type of steroids prescribed for inflammation (prednisone, prednisolone, dexamethasone), weaken bones through several simultaneous mechanisms. They suppress the cells that build new bone, ramp up the cells that break it down, and disrupt your body’s ability to absorb calcium. Fracture risk rises at doses as low as 2.5 mg of prednisone per day, and bone loss begins within the first few months of treatment.
Steroids Shut Down Bone-Building Cells
Your skeleton constantly remodels itself. Specialized cells called osteoblasts lay down new bone while osteoclasts break old bone down. Under normal conditions, these two processes stay roughly in balance. Glucocorticoids tip the scale decisively against bone formation.
At pharmacological doses, steroids suppress the genes that drive osteoblast maturation and function. They reduce production of collagen (the protein scaffold of bone), block growth factors that stimulate bone-building cells, and interfere with a critical signaling system called the Wnt pathway. This pathway acts like a green light for bone formation. Steroids dim that signal by suppressing key molecules, including one called Wnt16. In animal studies, restoring Wnt16 reversed the steroid-induced drop in bone formation, confirming it as a central target. Steroids also promote premature death of osteoblasts and osteocytes (the mature cells embedded in bone that sense mechanical stress and coordinate repair). The net result is that your body loses its ability to replace bone as fast as it’s being removed.
Bone Breakdown Accelerates at the Same Time
While bone formation slows, steroids simultaneously increase bone resorption. They do this by changing the chemical signals that osteoblasts send to osteoclasts. Osteoblasts normally produce two opposing signals: one that activates osteoclasts (RANKL) and one that blocks them (OPG, a decoy receptor). Steroids suppress OPG production while boosting RANKL. Prednisolone, for example, can increase RANKL expression roughly sevenfold in osteoblast cell lines. With less OPG to act as a brake, osteoclasts become more numerous, more active, and longer-lived. The bone dissolves faster than it can be rebuilt.
Calcium Balance Shifts Against You
Steroids also attack bone indirectly by disrupting calcium metabolism. They reduce calcium absorption in the intestines and increase calcium loss through the kidneys. This double hit creates a negative calcium balance, meaning your body is losing more calcium than it takes in. When blood calcium drops, your parathyroid glands respond by releasing more parathyroid hormone, which pulls calcium out of bone to restore blood levels. This secondary hyperparathyroidism adds yet another layer of bone loss on top of the direct cellular effects.
In some cases, high-dose steroid therapy can trigger outright hypocalcemia, with symptoms like muscle cramps, particularly in people who are already low in vitamin D.
Bone Loss Is Fastest in the First Year
The damage is front-loaded. Bone density drops most rapidly in the first three to six months of steroid therapy, driven primarily by the surge in osteoclast activity. In the first year alone, up to 20% of trabecular bone can be lost. After that initial period, the rate of loss slows but continues as long as steroids are taken, shifting to a pattern dominated by suppressed bone formation rather than excessive resorption.
Trabecular bone, the spongy, lattice-like tissue found inside vertebrae, the pelvis, and the ends of long bones, is hit hardest because it has a much higher surface area exposed to osteoclasts. This is why steroid users are especially vulnerable to vertebral compression fractures and hip fractures. Cortical bone (the dense outer shell of bones) is affected too, but more slowly.
Even Low Doses Raise Fracture Risk
There is no truly safe long-term dose. Fracture risk increases significantly at doses as low as 2.5 mg of prednisolone per day, and it climbs with both dose and duration. Current guidelines recommend that anyone taking the equivalent of prednisone 2.5 mg or more daily for three months or longer should be assessed for fracture risk. That assessment typically includes a bone density scan, a check for existing vertebral fractures (which can occur silently), and a fracture risk calculation for people over 40.
Importantly, steroids increase fracture risk partly independent of bone density. The disruption to osteocyte networks and bone quality means fractures can occur at bone density levels that wouldn’t normally be considered high risk. This is one reason steroid-induced osteoporosis is sometimes called a “bone quality” disease, not just a “bone quantity” disease.
Protecting Your Bones During Steroid Therapy
Prevention starts with calcium and vitamin D. The American College of Rheumatology recommends 1,000 to 1,200 mg of calcium per day (ideally from food, supplemented if needed) and 600 to 800 IU of vitamin D daily for anyone on long-term steroids. These don’t prevent bone loss on their own, but they correct the calcium deficit that steroids create and give medications a foundation to work with.
Lifestyle factors matter too: weight-bearing exercise, resistance training, maintaining a healthy weight, limiting alcohol, and not smoking all support bone density. Fall prevention becomes especially important since steroid-related muscle weakness (steroid myopathy) compounds fracture risk.
For people at moderate to high fracture risk, prescription treatment is strongly recommended. The main options are bisphosphonates (oral or intravenous), denosumab (an injection that blocks RANKL directly), and parathyroid hormone analogs (which stimulate new bone formation). Head-to-head comparisons between bisphosphonates and denosumab show similar fracture rates in the short term, though denosumab tends to produce slightly greater gains in bone density. For people at very high fracture risk, bone-building (anabolic) agents may be recommended as a first-line treatment rather than starting with bisphosphonates. The choice depends on your individual risk profile, other medical conditions, and how long you expect to be on steroids.
The single most effective strategy, when medically possible, is reducing the steroid dose or switching to a steroid-sparing treatment. Even modest dose reductions can meaningfully lower fracture risk, since bone loss is dose-dependent. If steroids are stopped, some bone density recovery is possible, though the rebound is often incomplete, particularly after prolonged use.