Osteoporosis is a disorder that causes bones to become porous, weak and brittle. It usually affects older adults and occurs when low levels of calcium, phosphorus and other minerals cause bones to lose mass. The early stage of decreased bone density is called osteopenia.

In most cases, osteoporosis does not cause pain. However, it can lead to fractures – most often in the spine, hip or wrist - that cause sudden, searing pain. Falls or minor events such as coughing, bending over or sneezing can break osteoporotic bones.

There are two main types of osteoporosis, according to the National Institutes of Health:

• Primary. Caused by aging (senile osteoporosis) or by unknown factors (idiopathic osteoporosis).
  
  
• Secondary. Caused by another disease, a medical treatment or lifestyle factors.

Osteoporosis is most common in women during and after menopause because lower levels of the hormone estrogen weaken bones. However, the disease also affects men and – in rare cases – children. In addition to aging, other contributors to osteoporosis include endocrine and many other disorders, a diet low in calcium and vitamin D, lack of weight-bearing exercise and use of certain drugs, such as corticosteroids taken by mouth for extended periods.

An estimated 44 million Americans are at risk for osteoporosis, or 55 percent of the population over age 55, according to the National Osteoporosis Foundation (NOF). Ten million Americans, 80 percent of them women, have been diagnosed with the disease.

One in two women and one in four men over the age of 50 will suffer an osteoporotic  fracture during their lifetime, according to the NOF. Osteoporosis is responsible for more than 1.5 million fractures in the United States each year, including about:

• 700,000 vertebral fractures
• 300,000 hip fractures
• 250,000 wrist fractures
• 300,000 fractures at other sites