Understanding Osteoporosis - The Basics

What Is Osteoporosis?

Osteoporosis, which means "porous bones," is a condition that causes bones to gradually thin and weaken, leaving them susceptible to fractures. About 1.5 million fractures occur each year due to osteoporosis.

Although all bones can be affected by the disease, the bones of the spine, hip, and wrist are most likely to break. In elderly people, hip fractures can be particularly dangerous because the prolonged immobility required during the healing process often leads to blood clots or pneumonia, both of which can be fatal.

Of the estimated 10 million Americans affected by osteoporosis, at least 80% are women. Experts believe women are more susceptible because their bones tend to be lighter and less dense, and because women's bodies experience hormonal changes after menopause that appear to accelerate the loss of bone mass.

What Causes Osteoporosis?

Although the exact cause of osteoporosis is unknown, the process by which bone becomes porous is well understood. Early in life, bone is broken down and replaced continuously, a process known as bone remodeling. Bone mass usually peaks in a person's late 20s.

Bone loss -- where bone breakdown is outpacing bone buildup -- occurs in the mid-30s. Bones begin to lose calcium -- the mineral that makes them hard -- faster than they can replace it. Less bone remodeling takes place, and the bones begin to thin.

For women, the loss of bone density speeds up during the first 5 to 7 years after menopause and then slows down again. Scientists believe that this rapid postmenopausal increase in bone loss is caused by a sharp decline in the body's production of estrogen, which appears to help keep calcium in the bones.

Although some loss of bone density is a natural part of aging, certain women are at higher risk for developing the very porous bones and bone fractures associated with osteoporosis. Women who are thin or have a small frame are at higher risk, as are those who smoke, drink more than moderately, or live a sedentary lifestyle. Women with a family history of osteoporosis and those who have had their ovaries removed, especially before age 40, are also more prone to the condition. White and Asian women are more frequently affected than African-American and Hispanic women.

Certain medical conditions that increase bone breakdown, such as kidney disease, Cushing's syndrome, and an overactive thyroid, can also lead to osteoporosis. Glucocorticoids, which are strong anti-inflammatory drugs used to treat conditions such as rheumatoid arthritis and asthma, also increase bone loss. Anti-seizure drugs and prolonged immobility due to paralysis or illness can also cause bone loss.