Anorexia nervosa, hyperprolactinemia, insulin-dependent diabetes, Cushing's syndrome, gastrectomy, osteogenesis imperfecta, mastocytosis, rheumatoid arthritis, long-term parenteral nutrition, hemolytic anemia, hemochromatosis and thalassemia, ankylosing spondylitis, multiple myeloma, Vitamin D deficiency, Paget's disease, primary hyperparathyroidism, hyperthyroidism, hypothyroidism, any cancer or any other major illness.