ABSTRACT
Osteoporosis is a condition of reduced bone density that is associated with micro-architectural changes that reduce bone quality, which leads to an increased risk of fracture. The process of bone loss begins after attaining peak bone mass around the age of 25-30 years. A gradual decline then occurs in all people as they age, mediated by a relative excess of bone resorption compared to bone formation (Figure 16.1). The definition of when this is a pathological condition is based on bone mineral density (BMD) measurements. A BMD of less than 2.5 standard deviations (SD) below the normal value for a person of the same sex aged 25 is defined as osteoporosis, and between 1.0 and 2.5 SD below the norm is termed 'osteopaenia'. Using this definition, around 30% of post-menopausal women are classified as having osteoporosis. 1 This data is derived from studies looking at Caucasian women, and their applicability to other groups is uncertain. People who fulfil this definition may have either failed to reach a normal peak bone mass, have a condition that has accelerated bone loss or have simply lived long enough for their bone density to have declined below this arbitrary level.
