GHK Cu vs AHK Cu: Which Copper Peptide Is More Effective? GHK Cu is a naturally occurring tripeptide in human plasma. Levels average 200 ng ml at age 20 and drop to 80 ng ml by age 60 (Pickart et al., 2020). That decline tracks with 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, OBM Geriatrics The Effect of the Human Plasma Molecule GHK Cu on Stem Cell Actions and Expression of Relevant Genes The Human Tripeptide GHKCu in Prevention of Oxidative Stress and Degenerative Conditions of Aging: Implications for Cognitive Health Pickart 2012 Oxidative Medicine and Cellular Longevity Wiley Online Library