IGF1 and osteoporosis: The hepatocyte response to GH produces IGF-1, the primary active form of GH action, and increased IGF-I levels are associated with tumors, whereas decreased levels are associated with the development of various diseases, such as type 2 diabetes, hypoglycemia, osteoporosis, cognitive decline, and coronary artery disease, thus demonstrating the complexity of the role of the human IGF axis.