Bone densityBone mineral density · BMD

Bone mineral density measures how much mineral is present per unit of bone, usually by DEXA scan at the hip and spine. Results are reported as a T-score against a young adult reference: below −1 is osteopenia, below −2.5 osteoporosis.

It matters because low density is the main modifiable predictor of fragility fracture, and a hip fracture in later life carries a serious mortality and independence cost. Density peaks in the late twenties and declines from there, with a sharp acceleration in women around menopause as oestrogen falls.

In practice bone responds to load. Resistance training and impact activity stimulate the osteoblasts that build bone, while swimming and cycling — excellent for other things — provide little of that signal. Adequate protein, calcium and vitamin D are the nutritional half of the picture.