Growth Hormone, Not IGF-1 Is the Key Longevity Regulator in Mammals

There are extraordinary examples of evolutionary conservation in biology, one of which is revealed in aging biology. A robust case in point are three interrelated endocrine systems that have been linked to longevity: the growth hormone (GH), insulin (INS), and insulin-like growth factor (IGF) pathways. As far down the evolutionary ladder as yeast, there is strong evidence that a carbohydrate regulatory system exists and that if perturbed, life-span extension is observed. Growth hormone is a pituitary-derived hormone that has both somatic and metabolic functions. Growth hormone has profound effects on lipid metabolism by promoting lipolysis and thus reducing fat mass; and the impact of GH on adiposity is distinct from that of IGF-1.