Part 1: Understanding Osteoporosis

Bone is a living, growing tissue. It consists of a matrix of fibers of the tough protein collagen, hardened with calcium, phosphorus and other minerals. Two types of architecture give bones strength. Surrounding every bone is a tough, dense compact outer layer of cortical bone. Inside is spongy-looking trabecular bone which is porous and forms the internal support system. Found in greater concentrations in flat bones such as the pelvis, vertebrae and ends of long bones, this trabecular bone is active metabolically. Its interconnecting structure provides much of the strength of healthy bone, but is especially vulnerable to osteoporosis.

The skeleton is not just a framework that supports the body and doesn't do much else. Every bit as dynamic as other tissues, bone responds to the pull of muscles and gravity, repairs itself, and constantly renews itself. Besides protecting internal organs and allowing us to move about, bone is also involved in the body's handling of minerals.

Of the 2 to 4 pounds of calcium in the body, nearly 99 percent is contained in the bones and teeth. The remaining 1% plays a critical role in blood clotting, nerve transmission, muscle contraction (including heartbeat), and other functions. The body keeps the blood level of calcium within a narrow range. When needed, bones release calcium. A complex interplay of many hormones balances the activity of the two types of cells--osteoclasts and osteoblasts--responsible for the continuous turnover process called remodeling. Osteoclasts consume old and worn bone, and osteoblasts manufacture new bone tissue.

Throughout a person's lifetime, old bone is resorbed and new bone is deposited to the skeleton in a process called remodeling. During childhood and adolescence, new bone is deposited faster than old bone is resorbed. Consequently, bones will become larger, heavier and denser. This bone formation continues at a pace faster than resorption until a person's peak bone mass (maximum bone density and strength) is reached in their 20's. Typically, by about 22 years of age, the average woman has acquired 99% of her bone density. Typically, by the age of 30, resorption will slowly begin to outpace deposition and density will decline. If someone didn't reach their peak bone mass during their critical bone-building years, they are much more likely to develop osteoporosis.

The skeleton is like a retirement account, but in our skeletal "account" we can deposit bone only during our first three decades. After that, all we can do is try to postpone and minimize the steady withdrawals. Osteoporosis is the bankruptcy that occurs when too little bone is formed during youth, or too much is lost later, or both.