Bone mineral density (BMD)

Bone mineral density is the amount of mineral — primarily hydroxyapatite — per unit area (g/cm²) or volume of bone tissue, most commonly assessed at the lumbar spine and femoral neck by DEXA. The T-score compares an individual's BMD to the young-adult mean peak reference; WHO criteria define osteopenia (T-score −1.0 to −2.5) and osteoporosis (T-score ≤ −2.5), the latter roughly doubling hip fracture risk per SD reduction. BMD declines with age, accelerating in women post-menopause; resistance and impact-loading exercise, adequate dietary calcium and vitamin D, and estrogen-related hormonal status are the principal modifiable determinants. Hip fracture in older adults carries ~20–30% one-year mortality, making BMD preservation a direct longevity target.