Frontiers Growth hormone insulin like growth factor I axis in health and disease states: an update on the role of intra portal insulin By age 30, your skin produces about 25% less collagen. By 40, that number can reach 40%. This decline affects more than just how your skin looks. It changes how it heals, The GH IGF 1 axis in ageing and longevity Nature Reviews Endocrinology GH and IGF 1 Regulation of Three Metabolic Pathways. GH inhibits Download Scientific Diagram