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 can lead to blood clots or pneumonia, both of which can have fatal consequences.
Osteopenia is a term used to describe bone density that is somewhat lower than normal -- but not low enough to be diagnosed as osteoporosis. Osteoporosis is a condition in which thinning bones become so fragile that they are prone to fracture easily. A person who has osteopenia is at risk for osteoporosis and may benefit from treatments to strengthen bone.
Of the estimated 8.9 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 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 mid to late 20s.
Bone loss -- where bone breakdown goes faster than bone buildup -- usually begins 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 five to seven 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 hip fracture 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 or parathyroid, can also lead to osteoporosis. Glucocorticoids, also known as steroids, also increase bone loss. Anti-seizure drugs and prolonged immobility due to paralysis or illness can also cause bone loss.