It is a common misconception that bone is a hard, lifeless structure.  Actually, bone is a complex, living tissue whose growth is affected by diet and exercise. The body is constantly building new bone tissue while breaking down or resorbing old bone. Until around age 30, the body builds and stores bone efficiently and total bone density is increasing or constant. Later in life, the body's bones begin to break down faster than new bone can be formed. In women, bone loss accelerates after menopause, when the ovaries stop producing estrogen, a hormone that helps maintain bone density. Bone is living tissue that is continually damaged by osteoclasts (cells responsible for destroying bone) and rebuilt rebuilt by osteoblasts (cells responsible for bone repair).  If this destruction/reconstruction process is unbalanced and bone loss is severe women may experience symptoms of osteoporosis.

Bone density and strength can change at an alarming rate.

• People who are bedridden for long periods of time can easily sustain fracture from minor activity such as walking. This is due to a weakening and loss of bone that occurs when patients do not receive adequate weight bearing activity.
• Astronauts who are in space for an extended period may experience bone loss due to the lack of gravitational pull and weight bearing on their body and bones.
• Computed tomography (CT) imaging has shown that tennis players have a larger bone cross section in the humerus of their playing arm than in the humerus of their non-playing arm. The larger, stronger humerus in the playing arm results from the added force applied to the bone from swinging the racket repeatedly.

Updated: April 7, 2008

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