The bones of the skeleton become thinner and weaker as a normal part of the aging process. The bone-building activity of the body begins to slow down between the ages of 30 and 40. Women lose roughly 8 percent of their skeletal mass every decade. Men lose about 3 percent per decade. Not all parts of the skeleton are equally affected. The vertebrae, jaws, and the area near the ends of bones (at the "growth plate") lose more bone tissue than other bones, resulting in a loss of height, loss of teeth, and limbs prone to fracture.