Editing Insulin-like growth factor 1 (section)

== Synthesis and circulation ==
{{see also|Neurobiological effects of physical exercise#IGF-1 signaling}}
The [[polypeptide hormone]] IGF-1 is synthesized primarily in the [[liver]] upon stimulation by [[growth hormone]] (GH). It is a key mediator of anabolic activities in numerous tissues and cells, such as growth hormone-stimulated growth, [[metabolism]] and protein translation.<ref name="cardiometabolic">{{cite journal | vauthors = Larsson SC, Michaëlsson K, Burgess S | title = IGF-1 and cardiometabolic diseases: a Mendelian randomisation study | journal = Diabetologia | volume = 63 | issue = 9 | pages = 1775–1782 | date = September 2020 | pmid = 32548700 | pmc = 7406523 | doi = 10.1007/s00125-020-05190-9 }}</ref> Due to its participation in the GH-IGF-1 axis it contributes among other things to the maintenance of muscle strength, muscle mass, development of the skeleton and is a key factor in brain, eye and lung development during fetal development.<ref name="Guo 1824–1830">{{Cite journal | vauthors = Guo J, Xie J, Zhou B, Găman MA, Kord-Varkaneh H, Clark CC, Salehi-Sahlabadi A, Li Y, Han X, Hao Y, Liang Y |date=2020-04-01 |title=The influence of zinc supplementation on IGF-1 levels in humans: A systematic review and meta-analysis  |journal=Journal of King Saud University - Science |volume=32 |issue=3 |pages=1824–1830 |doi=10.1016/j.jksus.2020.01.018 |issn=1018-3647}}</ref>

Studies have shown the importance of the GH/IGF-1 axis in directing development and growth, where mice with a IGF-1 deficiency had a reduced body- and tissue mass. Mice with an excessive expression of IGF-1 had an increased mass.<ref name="muskrats">{{cite journal | vauthors = Xie W, Tang Z, Guo Y, Zhang C, Zhang H, Han Y, Yuan Z, Weng Q | title = Seasonal expressions of growth hormone receptor, insulin-like growth factor 1 and insulin-like growth factor 1 receptor in the scented glands of the muskrats (Ondatra zibethicus) | journal = General and Comparative Endocrinology | volume = 281 | pages = 58–66 | date = September 2019 | pmid = 31121166 | doi = 10.1016/j.ygcen.2019.05.014 | s2cid = 163168020 }}</ref>

The levels of IGF-1 in the body vary throughout life, depending on age, where peaks of the hormone is generally observed during puberty and the [[postnatal period]]. After puberty, when entering the third decade of life, there is a rapid decrease in IGF-1 levels due to the actions of GH. Between the third and eighth decade of life, the IGF-1 levels decrease gradually, but unrelated to functional decline.<ref name="Guo 1824–1830"/> However, protein intake is proven to increase IGF-1 levels.<ref>{{cite journal | vauthors = Levine ME, Suarez JA, Brandhorst S, Balasubramanian P, Cheng CW, Madia F, Fontana L, Mirisola MG, Guevara-Aguirre J, Wan J, Passarino G, Kennedy BK, Wei M, Cohen P, Crimmins EM, Longo VD | title = Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population | journal = Cell Metabolism | volume = 19 | issue = 3 | pages = 407–417 | date = March 2014 | pmid = 24606898 | pmc = 3988204 | doi = 10.1016/j.cmet.2014.02.006 }}</ref>[[Image:IGF-1.GIF|thumb|right|3-d model of IGF-1]]