April 15, 2016

What is IGF-1?

IGF-1 (Insulin-Like Growth Factor) is a small polypeptide1,2 that is produced primarily in the liver in response to signals originating from the pituitary gland. IGF-1 synthesis can also be induced in other tissues in response to signals produced by nearby cells.1-3   IGF-1 plays a critical role in normal overall childhood growth, as well as in the proper regulation of adult cellular growth in almost all tissue types.*1-3  In addition, IGF-1 production can indicate nutritional status by signaling the availability of nutrients.*2,3

Is IGF-1 absorbed in the GI Tract?

Studies suggest that IGF-1 is stable and can be absorbed in the GI tract by neonates but clinical studies on adults are inconclusive. Two clinical studies4,5 reported that supplementation increased serum IGF-1 in healthy adults, but other studies were inconclusive. One reason could be that there are no standard pharmacokinetic studies evaluating the absorption of external supplementation with IGF-1 versus the IGF-1 synthesized in the body. These studies would need to be performed to confirm absorption

In which foods is IGF-1 normally found?

IGF-1 is typically found in dairy products, as well as in other foods of animal origin, such as meat and liver. 6,7

What is the source of NOW Foods IGF-1 available in spray and lozenge forms?

The IGF-1 used in NOW Foods products is extracted from deer antler velvet and comes from New Zealand.

Are there any specific precautions or contraindications associated with supplementary IGF-1?

NOW® IGF-1 products are intended for use by adults only and should be kept out of reach of children. These supplements are not meant for administration to pets. Do not use if you are pregnant or nursing; if you are taking medication or have a medical condition, consult your physician before using any of these products.

If you are a competitive athlete who is regularly tested, please check with your sanctioning body for the status of IGF-1. 


1. Nussey SS, Whitehead SA. Endocrinology: an integrated approach. Chapter 7: The Pituitary Gland. Taylor & Francis; 2001. 
2. Livingstone C. Clinical Science. 2013;125(6):265-280. 
3. Bartke A, Dominici F, Turyn D, Kinney B, Steger R, Kopchick J. Biogerontology. 2003;4(1):1-8. 
4. Mero, A, Kähkönen, J, et al. Journal of Applied Physiology. 2002;93(2):732-739.
5. Mero, A, Miikkulainen, H, et al. Journal of Applied Physiology.1997;83(4):1144-1151.
6. Ma J, Giovannucci E, Pollak M, et al. Journal of the National Cancer Institute. September 5, 2001 2001;93(17):1330-1336. 
7. Kang S, Kim J, Kim Y, et al. ASIAN AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES. 2007;20(1):119.