WHO defines osteoporosis as a marked reduction in bone density, to differentiate it from osteopenia which refers to mild reduction in bone density. In osteoporosis, the bone density is more than 2.5 standard deviations below the young normal mean (T scale <-2.5).

Osteoporosis is often known as the silent thief because bone loss occurs without symptoms.

True osteoporosis causes bone pain and or spontaneous fractures of the spine,hip and wrist.
Osteoporosis is usually asymptomatic until fracture develops.
Older persons with a fracture, especially spontaneous fracture of the spine, wrist or femur should be investigated for osteoporosis.

Prevalence
One in four women over the age of 50 has osteoporosis. One in eight men over 50 also has the disease. However, the disease can strike at any age.
More women die each year as a result of osteoporotic fractures than from breast and ovarian cancer combined.
A fifty-year-old woman has at least a 40 per cent risk of an osteoporotic fracture during the remainder of her life. Up to 20 per cent of individuals who fracture a hip, die as a result of complications. Fifty per cent of those who survive remain permanently disabled.