Insulin-like Growth Factor 1, also known as IGF-1, is used as a biomarker for blood levels of human growth hormone. The blood level of IGF-1 appears to be more constant over 24 hours than more rapidly fluctuating growth hormone and is found to be related to growth hormone secretion as a by-product of gh. It is a hormone produced by the liver and other tissues which affects growth-promoting activities and glucose metabolism. Because IGF-1 is related to the production and secretion of growth hormone (HGH), many doctors use this measurement to assess growth hormone status. Most hormone doctors who are experienced with the GH axis and growth hormone peptides consider an optimal IGF-1 level to be between 225ng-450ng for "anti-aging" purposes. IGF-1 can fluctuate significantly in a person in relation to their sleep quality, blood sugar, insulin level, and activity level. For example, high blood sugar and insulin suppresses IGF-1 while exercise increases IGF-1.