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Osteoporosis is a disease in which bones become fragile and more likely to break. Literally meaning "porous bone," it results in an increased loss of bone mass and strength. The disease often progresses without any symptoms or pain. If not prevented or if left untreated, osteoporosis can progress painlessly until a bone breaks. These broken bones, also known as fractures, occur typically in the hip, spine, and wrist; hip and spinal fractures in particular can have serious consequences.

Though osteoporosis occurs in both men and women, women are four times as likely to develop the disease than men. More than 24 million women in the United States are affected by this disease.

Thankfully, there are steps you can take to prevent osteoporosis from ever occurring. And if you have the disease, treatments—including prescription medications—can also slow the rate of bone loss.

This section has more information on:

  • Need-to-know anatomy
  • Causes
  • Risk factors
  • Need-to-know anatomy

    Our bones provide structural support for muscles, protect vital organs, and store calcium and other minerals. Bones are made of living, growing tissue. They're made mostly of collagen, a protein that provides a soft framework, and calcium phosphate, a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bones strong yet flexible to withstand stress. More than 99 percent of the body's calcium is contained in the bones and teeth. (The remaining 1 percent is found in the blood.) An outer shell of cortical or dense bone encases trabecular or spongy bone.

    When the body needs calcium, it breaks down and rebuilds bone. This process, called "bone remolding," supplies the body with needed calcium while keeping the bones strong. Bones are constantly changing; they can heal and may be affected by diet and exercise. When osteoporosis occurs, the "holes" in the spongy bone tissue grow larger and more numerous, weakining the internal structure of the bone.

    Think of your bones as a savings account. There is only as much bone mass in your account as you deposit.


    The critical years for building bone mass are from prior to adolescence to about age 30. Then, after about 35, as part of the natural aging process, your bones begin to break down faster than new bone can be formed. In women, bone loss accelerates after menopause, when the ovaries stop producing estrogen—the hormone that protects against bone loss. Osteoporosis develops when bone resorption occurs too quickly or if replacement occurs too slowly. It is more likely to develop if you did not reach optimal bone mass during your bone-building years.

    Men who have low testosterone levels, take prednisone, drink heavily or smoke a lot, or who have other medical conditions such as kidney stones (which are associated with calcium loss in the urine) are at risk for osteoporosis.

    When osteoporosis occurs, the "holes" in the "sponge" grow larger and more numerous as bone mass is lost at an accelerated rate, weakening the internal structure of the bone. That sets the stage for fractures.

    Risk factors

    Some risk factors for osteoporosis, such as advancing age, can't be changed. For more on these, see below. For those risk factors you can change, such as calcium intake, see our section on prevention.

    Gender: Women over the age of 50 have the greatest risk of developing osteoporosis. Women experience rapid bone loss during and five to 10 years after menopause, since menopause decreases the production of estrogen, a hormone that protects against excess bone loss. Osteoporosis is less common in men, but 20 percent of all hip fractures do occur in men.

    Age: Your risk for osteoporosis increases as you age.

    Race: Caucasian and Asian women are more likely to develop osteoporosis.

    Bone structure and body weight: Petite and thin people (body weight less than 127 pounds) have a greater risk of developing osteoporosis because they have less bone to lose than people with more body weight and larger frames.

    Family history: If your parents or grandparents have had any signs of osteoporosis, such as a fractured hip after a minor fall, you may have a greater risk of developing the disease.

    Medications: Certain drugs, including some corticosteroids and anticonvulsants, result in side effects that may damage bone and lead to osteoporosis.

    Testosterone: Men with low levels of this hormone are more likely to develop osteoporosis.

    Last reviewed on 12/12/2006

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