Osteoporosis is an age-related condition characterized by decreased bone mass and increased susceptibility to fractures. It does affect men but is more common in women after the menopause, predisposing older women particularly to fractures of the wrist, spine and hip (see ‘Menopause and postmenopause’). Osteoporosis is considered a major health problem and is increasing in prevalence due to changes in lifestyle, increasing longevity and the greater proportion of older people in the population. The prevalence of osteoporosis in women in the UK was 8.1% in 2002. Therefore, approximately 2.6 million women in England and Wales would have osteoporosis (NICE, 2004) and in the United States this figure would reach at least 20 million women (Turner et al., 2003).

Osteoporosis is usually defined, somewhat arbitrarily, by bone density measures (BDM) of bone mass lower than age-matched norms (typically BDM below −2.5 SD). However, fractures may not develop until the seventieth decade. Peak bone mass occurs at the age of 35, after which time bone repair becomes gradually less efficient. After the menopause, bone is lost more rapidly for about 3 to 5 years, and then slows down again. In women over 50 the risk of osteoporosis is estimated to be about one in three and approximately one in six for hip fracture. Risk factors for osteoporosis include low body mass index, current smoking, early menopause, family history of maternal hip fracture and long term systemic corticosteriod use and conditions affecting bone metabolism.