The word osteoporosis literally means "porous bones." It occurs when bones lose an excessive amount of their protein and mineral content, particularly calcium. Over time, bone density, and therefore bone strength, is decreased. As a result, bones become fragile and break easily. Even a sneeze or a sudden movement may be enough to break a bone in someone with severe osteoporosis.
Bone is a living tissue that is constantly being renewed and broken down throughout your life. During childhood and early adulthood, more bone is produced than removed, reaching its maximum mass and strength by the mid-30s. After that, bone is lost at a faster pace than it is formed, so the amount of bone in the skeleton begins to slowly decline.
The disease can affect any bone, but the most common locations are the hip, spine and wrist. Breaks in the hip and spine are of special concern because they almost always require hospitalisation and major surgery.
Osteoporosis occurs most often in older people and in women after the menopause. It affects nearly half of men and women over the age of 75. Women are about five times more likely than men to develop the disease. They have smaller, thinner bones than men and they lose bone mass more rapidly after the menopause (usually around the age of 50), when they stop producing estrogen, which is a bone protecting hormone. In the five to seven years following menopause, women can lose about 20% of their bone mass. By the age of 65 or 70, though, men and women lose bone mass at the same rate. So as you get older, bones become more fragile and are more likely to break.