Osteoporosis: Prevention, DEXA Scores, and Treatment Options

50 Percent of Women Over 50 Will Fracture a Bone Because of This Disease

Osteoporosis affects an estimated 200 million people worldwide and causes approximately 8.9 million fractures annually — one every three seconds. In the United States, 10.2 million Americans have osteoporosis and another 43.4 million have low bone mass (osteopenia), according to 2020 National Osteoporosis Foundation data. The lifetime fracture risk for a 50-year-old white woman is 50 percent — higher than her combined risk of breast cancer, uterine cancer, and ovarian cancer combined. Yet fewer than 20 percent of women who sustain an osteoporotic fracture receive appropriate bone-strengthening therapy afterward.

What DEXA T-Scores Mean

Bone mineral density (BMD) is most accurately measured by dual-energy X-ray absorptiometry (DEXA), typically at the lumbar spine (L1–L4) and proximal femur (femoral neck and total hip). The T-score compares a patient's BMD to the mean peak bone mass of a healthy 30-year-old of the same sex:

The Z-score compares BMD to age-matched peers — useful for identifying secondary causes of bone loss in younger adults. A Z-score below -2.0 warrants investigation for secondary osteoporosis (hyperparathyroidism, celiac disease, glucocorticoid excess, etc.).

DEXA has limitations. It measures areal bone density (g/cm²) rather than true volumetric density, meaning larger people appear to have higher BMD partly due to bone size. Vertebral fractures, scoliosis, and aortic calcification can artificially inflate lumbar spine T-scores, leading to underdiagnosis.

Peak Bone Mass: The Foundation Laid by Age 25–30

Approximately 90 percent of peak bone mass is acquired by age 18 in girls and age 20 in boys; the final 10 percent accrues through the mid-20s to early 30s. This peak determines lifelong fracture risk more than any other single factor. A 10 percent increase in peak bone mass delays osteoporosis onset by approximately 13 years. Factors that impair peak bone mass accrual include:

• Calcium and vitamin D deficiency during adolescence
• Low body weight or eating disorders in teenage years
• Glucocorticoid use (e.g., for asthma or inflammatory conditions)
• Amenorrhea (from any cause, including athletics or stress)
• Physical inactivity — impact loading is the primary mechanical stimulus for bone formation

The FRAX Tool: Absolute Fracture Risk

T-scores alone do not determine treatment decisions. The FRAX (Fracture Risk Assessment) tool, developed by the WHO Collaborating Centre at the University of Sheffield (2008), calculates 10-year probability of major osteoporotic fracture (spine, hip, forearm, humerus) and hip fracture alone. It integrates 12 clinical risk factors with or without BMD data:

• Age, sex, body mass index
• Prior fragility fracture
• Parental hip fracture history
• Current smoking and alcohol (>3 units/day)
• Glucocorticoid use (>5 mg prednisone for >3 months)
• Rheumatoid arthritis
• Secondary osteoporosis causes

In the United States, the National Osteoporosis Foundation recommends initiating pharmacotherapy when FRAX 10-year major fracture risk exceeds 20 percent, or hip fracture risk exceeds 3 percent, even in patients without T-scores meeting the -2.5 threshold.

Calcium Absorption: The Nuance

Calcium supplementation guidelines require more nuance than "take 1,000 mg daily." The body can only absorb approximately 500 mg of elemental calcium at one time — doses above this in a single serving are largely excreted. Total daily calcium needs for adults are 1,000 mg (ages 19–50), rising to 1,200 mg for women over 50 and all adults over 70. This should ideally come from dietary sources (dairy, fortified foods, leafy greens, sardines with bones), with supplements filling the gap only if diet is insufficient.

Calcium carbonate (the cheapest supplement) requires stomach acid for absorption and should be taken with food. Calcium citrate is absorbed independently of stomach acid and is preferred for individuals taking proton pump inhibitors or with reduced gastric acid. The 2013 U.S. Preventive Services Task Force found insufficient evidence that calcium plus vitamin D supplementation prevents fractures in community-dwelling adults without documented deficiency — and some data suggested possible cardiovascular risk signals with supplemental calcium above dietary needs. The practical message: prioritize dietary calcium first, supplement conservatively if necessary.

Bisphosphonate Drug Holidays: A Genuine Concern

Bisphosphonates — alendronate, risedronate, zoledronic acid, ibandronate — are first-line pharmacotherapy for osteoporosis. They bind hydroxyapatite in bone matrix and inhibit osteoclast-mediated resorption, increasing BMD and reducing fracture risk. Alendronate reduces hip fracture risk by 51 percent and vertebral fracture risk by 48 percent in clinical trials.

However, bisphosphonates accumulate in bone and suppress remodeling for years after discontinuation. Prolonged use (beyond 5 years) is associated with two rare but serious adverse effects:

Current guidelines (ASBMR 2022) recommend reassessing after 3–5 years of oral bisphosphonate therapy or 3 years of IV zoledronic acid. Low-risk patients (FRAX <3% hip, no prior vertebral fracture) can be considered for a drug holiday of 2–3 years while BMD and FRAX are monitored. High-risk patients should continue, switch, or extend with alternative agents (denosumab, romosozumab, teriparatide).

This article is for informational purposes only. Consult a qualified healthcare professional.