A bone mineral density (BMD) test measures the
mineral density (such as calcium) in your bones
using a special X-ray, computed tomography (CT)
scan, or ultrasound. From this information, an
estimate of the strength of your bones can be made.
Calcium is constantly being added to and taken away
from bone. When calcium is taken away faster than it
is added, the bones become lighter, less dense, and
more porous. This makes the bones weaker and
increases their risk of fracture.
Loss of bone mass occurs as part of the natural
process of aging. Bones naturally become thinner
(called osteopenia) as you grow older, because
existing bone is broken down faster than new bone is
made. As this occurs, the bones lose minerals,
heaviness (mass), and structure, making them weaker.
With further bone loss, osteopenia develops into
osteoporosis. The thicker your bones are, the longer
it takes to develop osteoporosis. Although
osteoporosis can occur in men, it is most common in
women older than age 65.
Regular X-rays cannot detect mild bone loss. A
bone must lose at least a quarter of its weight
before a regular X-ray can detect the problem.
