Insulin-like growth factor 1 is so-called because its structure resembles that of insulin. Created in the liver under direction of growth hormone, IGF-1 is a nicely anabolic hormone for pretty much every cell in the body, especially muscle. If you need a quick primer on vitamin D, check out the article Sun, sea and sex drive. As noted above, the study that article is based on found a correlation between sufficient vitamin D intake and serum androgen levels in men.
Some new research coming out of the University of Pisa, Italy is showing the same effect on IGF-1 levels. The subjects with vitamin D deficiency had lower levels of IGF-1 than those with adequate, or almost adequate, vitamin D levels. This highlights another reason why you should be regularly getting yourself into the sunshine as much as possible, especially with it being summer time in the Northern hemisphere right now! Alternatively, get yourself a reputable brand of Vitamin D3.
The research is due to be published in the Journal of Endrocrinological Investigation soon.
Source: Bogazzi F, Rossi G, Lombardi M, Tomisti L, Sardella C, Manetti L, Curzio O, Marcocci C, Grasso L, Gasperi M, Martino E. VITAMIN D STATUS MAY CONTRIBUTE TO SERUM IGF1 CONCENTRATIONS IN HEALTHY SUBJECTS. J Endocrinol Invest. 2010 Jul 29. [Epub ahead of print]