What Is Osteoporosis?
Osteoporosis is a skeletal disease characterised by reduced bone density and deterioration of bone microarchitecture, leading to increased bone fragility and fracture risk. Bone is living tissue, constantly remodelled through a balance of osteoclast activity (bone breakdown) and osteoblast activity (bone formation). Osteoporosis occurs when bone resorption chronically exceeds formation — either because peak bone mass was never reached, because bone loss accelerated (particularly after menopause), or both.
Approximately 200 million people worldwide are affected by osteoporosis. It causes an estimated 8.9 million fractures annually. Hip fractures carry the most serious consequences: 20–30% of patients die within one year; 50% never regain their prior level of independence.
Risk Factors
Non-Modifiable
- Female sex (4× higher prevalence than men)
- Postmenopausal status — oestrogen maintains bone density; its loss accelerates bone resorption
- Age — bone density peaks at 25–30 and declines thereafter
- White or Asian ethnicity (lower peak bone mass)
- Family history of osteoporosis or fragility fracture
- Prior fragility fracture (strongest predictor of future fracture)
- Early menopause (<45 years) or primary hypogonadism in men
Modifiable
- Low calcium and vitamin D intake
- Physical inactivity — weight-bearing exercise maintains bone density
- Smoking — directly toxic to osteoblasts
- Excessive alcohol (>3 units/day)
- Low body weight (BMI <19)
- Falls risk factors (poor balance, muscle weakness, medications causing dizziness)
Secondary Causes (Diseases and Medications)
- Long-term glucocorticoid use (prednisolone ≥5 mg/day for ≥3 months) — most common drug cause
- Rheumatoid arthritis
- Coeliac disease and inflammatory bowel disease (malabsorption of calcium/vitamin D)
- Chronic kidney disease
- Hyperparathyroidism
- Type 1 diabetes
- Proton pump inhibitors (long-term use modestly increases fracture risk)
- Aromatase inhibitors (breast cancer treatment) and androgen deprivation therapy (prostate cancer)
Diagnosis: DEXA Scan and T-Scores
Dual-energy X-ray absorptiometry (DEXA) measures bone mineral density (BMD) at the hip and lumbar spine. Results are reported as T-scores — the number of standard deviations above or below the mean BMD of a young healthy adult:
- T-score ≥ −1.0: Normal
- T-score −1.0 to −2.5: Osteopenia (low bone density; increased fracture risk)
- T-score ≤ −2.5: Osteoporosis
- T-score ≤ −2.5 with prior fragility fracture: Severe osteoporosis
DEXA alone does not capture all fracture risk. The FRAX tool (fracture risk assessment tool; freely available online) integrates BMD with clinical risk factors to calculate the 10-year probability of hip fracture and major osteoporotic fracture — guiding treatment decisions.
Prevention: The Evidence Base
Calcium
Adequate calcium intake is essential throughout life. Recommended daily intakes: 1,000 mg/day for adults, 1,200 mg/day for women >50 and men >70. Dietary sources are preferable to supplements — dairy products, fortified plant milks, sardines, kale, almonds. High-dose calcium supplements (>1,000 mg/day) may slightly increase cardiovascular risk; supplements should fill dietary gaps rather than replace food sources.
Vitamin D
Vitamin D is essential for calcium absorption. Deficiency is widespread, particularly in northern latitudes, dark-skinned individuals, and the elderly. The UK recommends 400 IU/day for the general population; 800–1,000 IU/day is recommended in osteoporosis management guidelines. A meta-analysis shows that combined calcium and vitamin D supplementation (not D alone) reduces hip fracture risk by approximately 15–18% in older adults.
Exercise
Weight-bearing exercise (walking, jogging, dancing, resistance training) maintains and modestly increases bone density. Resistance training has the strongest evidence — particularly hip and spine exercises. Exercise also reduces falls risk through improved muscle strength and balance. Tai Chi is specifically recommended for fall prevention in older adults.
Pharmacological Treatment
Treatment is generally recommended for postmenopausal women and men >50 with:
- T-score ≤ −2.5
- Prior hip or vertebral fracture
- FRAX 10-year hip fracture risk ≥3% or major osteoporotic fracture risk ≥20%
- Long-term glucocorticoid use
Bisphosphonates (First-Line)
Alendronate (weekly oral), risedronate, zoledronic acid (annual IV infusion). Inhibit osteoclast activity; reduce vertebral fractures by 40–70% and hip fractures by 40%. Well-tolerated; rare risk of atypical femoral fracture and osteonecrosis of the jaw with very long-term use. Drug holidays (after 3–5 years) are considered in low-to-moderate risk patients.
Denosumab (RANKL Inhibitor)
Subcutaneous injection every 6 months; highly effective; does not accumulate in bone so must not be stopped abruptly — discontinuation causes rapid bone loss and rebound vertebral fractures. Requires transition to a bisphosphonate when stopping.
Anabolic Agents (Severe Osteoporosis)
- Teriparatide (PTH analogue) — daily subcutaneous injection for up to 2 years; stimulates new bone formation; reserved for severe cases; followed by antiresorptive therapy
- Romosozumab (sclerostin inhibitor) — monthly injections for 1 year; dual action (builds bone and reduces resorption); used in very high fracture risk; caution in cardiovascular disease