Osteoporosis is a disorder that causes weak bones. The word osteoporosis means bone (osteo) that is porous or filled with holes (porosis). If you have osteoporosis, the holes and spaces in your bones are much bigger than in healthy bone. This means your bones have lost density or mass. As your bones become less dense, they become weaker, increasing your risk of fracture. Any bone can be affected with these fractures, but they most typically occur in the hip, spine and wrist.

For some people affected by the disease, simple activities such as lifting a child, bending down to pick up a newspaper, bumping into furniture or even sneezing can cause a bone to break.

To understand how osteoporosis occurs, it’s important to understand the normal life cycle of bone. Bone is a living tissue; its cells die and are replaced regularly in a process called bone turnover. From childhood into young adulthood, your body produces more than enough cells to replace those that die, resulting in stronger, denser bones.

By the time you are 25, your bones are as strong as they will ever be (called peak bone mass). Your bone turnover remains fairly stable for several years. Then, at about age 40, bone cells start to die at a more rapid rate than new cells are produced. This starts a slow decline in bone mass.

After menopause, a drop in estrogen levels in women results in a rapid decline in bone mass. Men, too, experience a decline in bone mass as sex hormone levels decline, but this decline is typically less rapid and less severe. According to the National Osteoporosis Foundation, women are four times more likely than men to develop the disease. By age 80, women have lost about 40 percent of their peak adult bone mass, and men have lost about 25 percent.

The weak bones may lead to a hump in the upper back (dowagers hump), loss of height and increased risk of fractures (broken bones). The spine, hips, ribs and wrists are the most common fractured bones, although osteoporosis-related breaks can occur in almost any bone in the body. Osteoporosis itself is painless, but the fractures that may accompany it are not.

Osteoporosis is different from osteoarthritis (OA), a common form of arthritis in which joint cartilage – the rubbery material that covers the ends of bones – erodes. Eventually the bone ends rub together, causing joint pain and stiffness.