Roughly 10 million people in the United States suffer from osteoporosis. Postmenopausal women are the most commonly affected individuals; however, men also face an increased incidence of the disease as a result of advancing age.

Fractures due to osteoporosis are deadly. Mortality rates are increased more than 7-9 times normal after osteoporosis related fractures of the hip or spine. And of those people who survive, more than half lose the ability to function normally and 25% end up in nursing homes.

Risk factors for osteoporosis include: female gender, advancing age, family history of the disease, Caucasian or Asian race, small body structure, chronic kidney disease, poor health, lack of mobility, alcoholism, cigarette smoking, high caffeine intake. Other risk factors include low calcium intake or reduced calcium absorption from the intestine, chronic steroid or blood thinner use, and history of falls.

The major determinant of risk of fracture is the strength of bone. Bone strength is a function of both the quantity as well as quality of bone.

Bone formation starts as the fetus develops and continues throughout childhood and adolescence. Peak bone mass is achieved in early adulthood, around the age of 30.

Bone is a living tissue that is continually being renewed. Old bone is removed and new bone takes its place. The structure of bone can be viewed as being like a house. A framework, called the matrix, is filled in with "bricks" consisting of minerals such as calcium and phosphorus.

In healthy adults the rate of removal of old bone is matched by the laying down of new bone. With aging, though, the amount of new bone formation slows and there is a net loss of bone mass over time.

Osteoporosis occurs when there is an excessive amount of bone removal so that the bone develops small cavities. This leads to a loss of bone strength and increased risk for fracture.

The diagnosis and treatment of osteoporosis will be discussed in other articles.