Bone Density and Osteoporosis: What You Need to Know

Intro

Bone is living tissue that continuously remodels throughout life — old bone is broken down and replaced by new bone. In younger years, formation outpaces resorption, building towards peak bone mass. After midlife, the balance shifts, and bone density gradually declines.

Osteoporosis is a condition defined by low bone density and deterioration of bone microstructure, leading to increased fragility and fracture risk.

Osteoporotic fractures — especially of the hip, spine, and wrist — are a major cause of disability, loss of independence, and mortality in older adults. Hip fractures in particular carry a one-year mortality rate of around 20–30%.

Osteoporosis is largely preventable and treatable, but it is often undetected until a fracture occurs. Earlier identification and intervention can substantially reduce fracture risk.

Key Points

Peak bone mass is reached in the late 20s to early 30s; bone density then gradually declines with age.
Osteoporosis is diagnosed by DEXA scan using T-score thresholds.
Women lose bone rapidly in the years following menopause due to estrogen decline.
Fracture risk depends on both bone density and other clinical risk factors.
The FRAX tool calculates 10-year fracture probability using multiple risk factors.
Calcium, vitamin D, and weight-bearing exercise support bone health across life.
Bisphosphonates are the most widely prescribed first-line pharmacological treatment.

Background

Bone consists primarily of collagen fibers reinforced by calcium phosphate crystals, giving it both flexibility and hardness. Specialised cells called osteoblasts build bone, while osteoclasts resorb it. This remodeling cycle is regulated by hormones, mechanical loading, and nutritional factors.

Peak bone mass — the maximum density achieved during adulthood — is the single strongest predictor of bone density in later life. Genetics accounts for roughly 60–80% of peak bone mass variability. The remainder is influenced by physical activity, calcium and vitamin D intake, and other factors during childhood and adolescence.

Bone loss begins gradually in the mid-30s in both sexes. In women, the pace accelerates significantly in the first 5–10 years after menopause, driven by falling estrogen. Men lose bone more slowly and on average develop osteoporosis about 10 years later than women.

Causes and Risk Factors

Primary osteoporosis is age-related and includes postmenopausal osteoporosis and age-related (senile) osteoporosis.

Secondary osteoporosis arises from an underlying condition or medication:

Glucocorticoid (steroid) therapy — the most common drug cause
Hyperparathyroidism, hyperthyroidism
Celiac disease, inflammatory bowel disease (malabsorption)
Chronic kidney disease, liver disease
Hypogonadism in men (low testosterone)
Eating disorders, anorexia

Non-modifiable risk factors:

Female sex
Increasing age
White or Asian ethnicity
Family history of osteoporosis or hip fracture
Prior fragility fracture

Modifiable risk factors:

Low physical activity
Smoking
Excess alcohol (more than 3 drinks/day)
Low body weight
Low calcium or vitamin D intake
Falls risk (muscle weakness, balance problems, medications)

Diagnosis and Measurement

DEXA scan (dual-energy X-ray absorptiometry) DEXA is the standard method for measuring bone mineral density (BMD). It typically measures the lumbar spine and hip. Results are expressed as T-scores and Z-scores:

T-score: compares BMD to a young-adult reference population (same sex)
Z-score: compares BMD to age-matched peers

WHO diagnostic categories (based on T-score):

Normal: T-score above −1.0
Osteopenia (low bone mass): T-score between −1.0 and −2.5
Osteoporosis: T-score at or below −2.5
Severe osteoporosis: T-score at or below −2.5 plus a fragility fracture

FRAX tool The FRAX calculator (developed by WHO) estimates a person’s 10-year probability of a major osteoporotic fracture or hip fracture. It incorporates T-score, age, sex, BMI, prior fracture, parental hip fracture history, smoking, glucocorticoid use, rheumatoid arthritis, and secondary osteoporosis causes.

FRAX is widely used to guide treatment decisions, particularly in people with osteopenia.

Screening recommendations Most guidelines recommend DEXA screening for:

Women aged 65 and older
Younger postmenopausal women with risk factors
Men aged 70 and older, or younger men with significant risk factors
Anyone who has sustained a fragility fracture

Treatment and Prevention

Non-pharmacological

Weight-bearing and resistance exercise Physical activity — particularly weight-bearing exercise (walking, jogging, dancing) and resistance training — stimulates bone formation and slows bone loss. Balance training reduces falls risk.

Calcium intake Adequate dietary calcium is important throughout life. The recommended intake for adults is approximately 1000 mg/day, rising to 1200 mg/day for women over 50 and men over 70. Food sources are preferred over supplements where possible.

Vitamin D Vitamin D is required for calcium absorption. Deficiency is common in older adults, particularly those with limited sun exposure. Supplementation is generally recommended for older adults, with 800–2000 IU/day commonly suggested.

Smoking cessation and alcohol reduction Both smoking and heavy alcohol use are associated with lower bone density and higher fracture risk.

Fall prevention For older adults, reducing falls is as important as improving bone density. Strategies include home safety assessment, reducing sedating medications, exercise programs targeting balance and strength, and reviewing vision.

Pharmacological

Bisphosphonates The most commonly prescribed first-line treatment. They reduce osteoclast activity, slow bone resorption, and reduce fracture risk by around 40–70% at vertebral sites. Examples: alendronate, risedronate, zoledronic acid. Generally well tolerated; rare side effects include atypical femoral fractures and osteonecrosis of the jaw with very long-term use.

Denosumab A monoclonal antibody that inhibits osteoclast formation. Given as a subcutaneous injection every 6 months. Effective at reducing fracture risk. Bone density may fall quickly if discontinued without transitioning to another agent.

Hormone replacement therapy (HRT) Estrogen therapy prevents bone loss in postmenopausal women and reduces fracture risk. Its use for osteoporosis is balanced against other considerations such as cardiovascular and breast cancer risk; decisions should be individualised.

Teriparatide and romosozumab Anabolic agents that stimulate bone formation rather than simply reducing resorption. Used in severe osteoporosis or when antiresorptive agents have failed. More expensive and typically specialist-initiated.

Risks and Prognosis

Fragility fractures A fragility fracture — one occurring from a minor fall or without significant trauma — is itself a strong predictor of future fractures. Vertebral fractures are often silent and found incidentally on imaging.

Hip fractures Hip fractures are the most clinically serious osteoporotic fracture. Around 20–30% of patients die within one year. Many survivors experience lasting functional limitation.

Treatment response DEXA monitoring (typically every 1–2 years during treatment) allows assessment of response. Gains in bone density reduce fracture risk, but fracture reduction may occur even before large changes in T-score are seen.

Long-term drug use Bisphosphonates accumulate in bone and may be effective for extended periods. Drug holidays are sometimes considered after 3–5 years of treatment in lower-risk individuals; higher-risk patients typically continue treatment.

FAQ

Q: Is osteopenia the same as osteoporosis? A: No. Osteopenia refers to bone density that is lower than average for a young adult but not yet in the osteoporosis range. It indicates increased risk but does not always require medication — decisions depend on overall fracture risk.

Q: Can you develop osteoporosis if you’ve always exercised and eaten well? A: Genetics has a strong influence on peak bone mass. Some people develop osteoporosis despite good lifestyle habits, particularly if they have secondary causes or a strong family history.

Q: Are calcium supplements safe? A: For most people, moderate calcium supplementation is safe. Some studies have raised questions about cardiovascular risk from high-dose supplements, though evidence is mixed. Dietary calcium is generally preferred.

Q: Does dairy consumption prevent osteoporosis? A: Dairy is a good dietary source of calcium, and adequate calcium intake supports bone health. However, high dairy consumption alone does not guarantee protection from osteoporosis, especially if other risk factors are present.

Q: At what age should I get a DEXA scan? A: Most guidelines recommend screening for women at 65 and men at 70. Earlier screening is appropriate if significant risk factors are present, including prior fragility fracture, long-term steroid use, or family history.

Q: Can osteoporosis be reversed? A: Treatment can increase bone density and substantially reduce fracture risk, but it rarely normalises T-scores to the young-adult range. The goal is fracture prevention and preservation of function.