In a recent editorial in the British Medical Journal, several experts from the University of Bristol in England write about the substantial and still growing body of evidence implicating insulin-like growth factor-I (IGF-1) in cancer.
They note that the role of IGF-1 in promoting cancer has been investigated for many years, but recently the quality and quantity of evidence has increased
They note that several prospective studies have used stored blood collected up to 14 years before the onset of cancer have shown associations between IGF-1 and prostate cancer, premenopausal breast cancer, and colon cancer.
According to the editorial, "The risk of cancer is higher among people with raised concentrations of insulin-like growth factor-I".
In addition, "it is lower among those with high concentrations of insulin-like growth factor binding protein-3 (the main binding protein)."
Research suggests that the observed relation between cancer and IGF-1 is not due to the release of the growth factor by the cancer itself.
"The effects are sizeable and stronger than the effects seen in relation to most previously reported risk factors" they state.
In addition to the increasing direct epidemiological evidence, there is a significant amount of circumstantial evidence.
Acromegaly, in which high concentrations of growth hormone stimulate production of high concentrations of IGF-1, has been associated with an increased risk of colorectal cancer and breast cancer in some studies and less consistently with prostate, thyroid, and hematological malignancies. In many studies anthropometric markers of the activity of insulin-like growth factor-I, such as height and leg length, are associated with cancer incidence, particularly with the cancers for which risk increases with rising concentrations of insulin-like growth factor-I. In animals, calorie restriction reduces the risk of cancer primarily by reducing the circulating concentrations of insulin-like growth factor-I" the editorial notes.
Acromegaly, in which high concentrations of growth hormone stimulate production of high concentrations of IGF-1, has been associated with an increased risk of colorectal cancer and breast cancer in some studies and less consistently with prostate, thyroid, and hematological malignancies.
In many studies anthropometric markers of the activity of insulin-like growth factor-I, such as height and leg length, are associated with cancer incidence, particularly with the cancers for which risk increases with rising concentrations of insulin-like growth factor-I.
Some of the potential mechanisms of the way in which IGF-1 increases cancer risk are as follows:
IGF-1 could be a surrogate for the activity of sex steroid hormones, which in turn influence the risk of cancer. IGF-1 may increase cell turnover and the susceptibility of cells to malignant transformation both directly and by modulating the effects of sex steroids. IGF-1 might increase the risk of cancer by preventing the programmed death of cells that have been transformed, thus interrupting an important process, which retards the development of cancer.
IGF-1 could be a surrogate for the activity of sex steroid hormones, which in turn influence the risk of cancer.
IGF-1 may increase cell turnover and the susceptibility of cells to malignant transformation both directly and by modulating the effects of sex steroids.
"Given the increasing evidence of the risk of cancer, caution should be exercised in the exogenous use of either insulin-like growth factor-I or substances that increase concentrations of it," they state.
British Medical Journal October 7, 2000;321:847-848
It is also interesting to note that the growth hormone that is so strongly promoted by many anti-aging clinicians may in fact have adverse effects by raising insulin-like growth factor-I. It is probably best for most to avoid the use of growth hormone and rely on more proven and less risky interventions, like a good diet which reduces insulin levels and also weight training which can increase growth hormone.
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