Osteoporosis is a disease in which the density and quality of bone are reduced, leading to weakness of the skeleton and increased risk of fracture. Osteoporosis literally means "porous bone". When a bone has become osteoporotic or osteopenic (low bone mass), the risk of a fracture increases. The forearm, spine and hip are the most common fracture sites, accounting for more than 80 percent of all fractures. Osteoporosis and associated fractures are an important cause of mortality and morbidity. 20 percent of hip fractures lead to death within a year.

In many affected people, bone loss is gradual and without symptoms or warning signs until the disease is advanced. Osteoporosis is a global problem which is increasing in significance as the population of the world both grows and ages. For these reasons, osteoporosis is often referred to as the "silent epidemic". In the US alone, 44 million have either osteoporosis or low bone mass. These 44 million represent 55 percent of the population aged 50 and over. It is estimated that by 2010 the number of people with osteoporosis or low bone mass will have increased to 52 million in the US.

Many people think of osteoporosis as an "an old woman's disease". This is an old misconception. Bone loss in women can begin as early as age 25. Worldwide, the lifetime risk for a woman to have an osteoporotic fracture is 30-40 percent. In men the risk is about 13 percent. In the US, more than 14 million men have osteoporosis or low bone mass. This number is expected to increase by more than 20 percent to 17 million in 2010.

Osteoporosis is a widespread public health problem. The costs to national healthcare systems from osteoporosis-related hospitalization are staggering. In the US, the cost to the health care system associated with osteoporotic fractures is approximately $17 billion annually. This converts to more than $45 million a day! Each hip fracture represents an estimated $40,000 in total medical costs.