False-colour X-ray of the deformed thoracic spine of a woman suffering from osteoporosis. Osteoporosis describes a reduction in bone density, resulting in an increase in brittleness and a greater risk of fractures, particularly of the vertebrae, hip or arm. The condition arises through an imbalance between formation & resorption of bone, most commonly occurring with increasing age. The incidence is greater in women than in men and is attributed to a decline in hormone production following the menopause. Osteoporosis may be prevented and treated by hormone replacement therapy (HRT) using various preparations of female sex hormones.