Abstract

Insulin-like Growth Factor 1 is a hormone which can mediate cell growth and multiplication. In the context of muscle and cartilage growth, it is anabolic, most notably via an increase in the rate of protein synthesis.

There is some scientific research which suggests IGF-1 is the principal growth hormone and that it acts independently to pituitary GH as well as synergistically alongside it.

With respect to other health effects, research is in its infancy and a mixture of both positive and negative effects have been found. Nothing is conclusive at this stage.

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IGF-1: Insulin-like Growth Factor 1

IGF-1 is a hormone in the form of a protein which has a very similar structure to insulin. Proteins are coded by our genes and we have a specific IGF-1 gene which codes its protein.

Proteins, such as insulin and IGF-1 are like keys, and the genes that code them are like the key-cutters. Like keys, they fit a matching lock, and the locks are called receptors. The receptors tend to have very unoriginal names like Insulin-like Growth Factor 1 Receptor, or IGF1R.

The receptors can be found all throughout the body in different kinds of cells and tissues, and when proteins bind with them, their programmed behaviour can be exerted. As IGF-1 is very similar to insulin, it can actually fit the same lock as insulin, i.e. it can bind to Insulin’s receptor as well as its own, but it does so much more weakly than insulin does.

IGF-1 Binding Proteins – IGF1BP

There are several (current research indicates 7) binding proteins which modulate the availability of IGF-1 to the tissues it interacts with. Most (about 80%) of IGF-1 binds to IGFBP-3 which is regulated by pituitary GH, and to some degree IGF-1 itself.

Some supplement manufacturers develop products which inhibit the binding proteins – especially IGFBP-3 – in order to elevate the levels of free form IGF-1, the theory being that the binding protein itself inhibits the uptake of IGF-1 to the target cells.

Natural IGF-1 Production

IGF-1 is mainly produced in the liver, stimulated by Human Growth Hormone (HGH). A little is produced by other tissues. Several factors can inhibit its production and release, including poor nutrition, insensitivity to HGH and lack of the receptors.

As well as the liver, the cartilaginous cells secrete IGF-1 and it can be regulated in an autocrine (cell releases hormone and binds it to receptor on same cell to change it in some way) , paracrine (like autocrine but local cell to cell signalling) and endocrine (like paracrine but whole body wide) manner.

Supplement Industry Implications

Research into the exact behaviour of IGF-1 and its related components is always ongoing. The ergogenic supplement industry is manufacturing, promoting and marketing products based on results from first phase scientific studies.

If you are looking for an ironclad, placebo controlled, double blind, randomized studies with well trained humans, investigating the effects of something which might inhibit a binding protein of IGF-1, you are not going to find it.

Potential Health Effects

The effect of IGF-1 on cell multiplication and growth has excellent implications for someone building muscle. Research has led to further potential impacts on our health.

IGF-1 has been shown to improve the health of the digestive tract and is being investigated further as a possible treatment for bowel disease. However, some scientists have linked it with a few deleterious effects such as the proliferation of certain cancers and heart disease, the theory being that the cells it exerts growth activity toward are not always ‘good’ cells. An increased risk of diabetes has also been noted in one study, but another investigation implied it has beneficial effects on insulin sensitivity, therefore preventing diabetes. As you can see, more research is needed.

The takeaway point here is that IGF-1 is not even close to being fully understood, and it is early days yet with respect to the research. Our best advice is to ‘watch this space’ for now and see what develops in the world of IGF-1.

As for the currently marketed supplements which are advertising a boost in free IGF-1 levels, we cannot comment in a medical capacity on the benefits and risks of such products. However, we would find it difficult to believe the IGF-1 boost achieved from a supplement could be even in the same ballpark as the concentrations used in laboratory research.

Conclusion

IGF-1 is a growth hormone which can increase cell volume and replication, which translates to higher protein synthesis rates and anabolism in muscles. It appears to act both separately and in conjunction with Growth Hormone. Early research indicates that it may have both positive and negative effects on other aspects of health. Research is ongoing.

Final comment: These days, what can you ingest that doesn’t have research backing both negative and positive effects? Turmeric, maybe, off the top of my head, is a true superfood.

Alternative Names

IGF-1: aka – Somatomedin, sulfation factor
HGH: aka – GH, growth hormone, human growth hormone, Somatropin

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Sources

http://en.wikipedia.org/wiki/Insulin-like_growth_factor_1
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187088/
http://www.ncbi.nlm.nih.gov/pubmed/9402139
http://www.ncbi.nlm.nih.gov/pubmed/1381713
http://en.wikipedia.org/wiki/Autocrine_signalling
http://en.wikipedia.org/wiki/Paracrine_signalling
http://www.medscape.com/viewarticle/732476_3