Corticosteroids act on a host of nuclear receptors Intracellular receptor proteins that bind to hydrophobic signal molecules (such as steroid and thyroid hormones) or intracellular metabolites and are thus activated to bind to specific DNA sequences which affect transcription. , activating some and inactivating others. For example, cortisol has an affinity for the glucocorticoid receptor, and aldoesterone has an affinity for the mineralocorticoid receptor. Corticosteroids also bind to other key receptors including the Vitamin D Receptor, PPAR-alpha, PPAR-gamma, and others.
Osteoporosis is particularly common in smokers, postmenopausal women, the elderly, underweight or immobile, and patients with diabetes or lung problems. Osteoporosis may result in fractures of the spine, ribs or hip joint with minimal trauma. These occur after the first year in 10–20% of patients treated with more than mg prednisone daily. It is estimated that up to 50% of patients on long-term prednisone will develop bone fractures. Vertebral fractures are more common in patients on steroids, even in those with normal bone density.