Positive Health Online

We all know that there are certain white products that we really ought not to include in our diet. Salt and sugar come top of the list. And then there is white flour, white rice and white pasta.

Several studies now indicate that another white substance, milk, should also be on the 'white list' of dietary no-nos. Current research has linked Insulin-like Growth Factor 1 (IGF-1) which is found in milk, to prostate cancer, [1,2] premenopausal breast cancer[2] and colon cancer.[2] It has further been argued that increased risks of contracting these cancers may be programmed from early life.3 Indeed some authors like Professor Jane Plant4 argue that all dairy should be cut entirely from the diet.

So just what is IGF-1, and why is milk thought to be linked to certain cancers?

IGF-1 (there is also IGF-2) is one of the most highly concentrated of the protein hormones in the blood. It has profound effects on stimulating growth and metabolism and influencing many aspects of our health. IGFs, for example, mediate the effects of growth hormone on childhood growth. Milk contains several hormones and growth factors and this includes IGF-1. IGF-1 is one of the most important hormone signallers in the body, but circulating levels in the blood have to be right. Too little, for example if you are on a restrictive diet that excludes animal fats and protein, and there is the increased risk of cardiovascular disease, type-2 diabetes, osteoporosis and cognitive decline. Too much, because of a diet containing a high intake of dairy perhaps, and the risk of breast, colon and other cancers are increased.

When we drink milk most of the hormones and growth factors within the milk are digested, with only a small amount, protected in the gut by the milk protein casein, passed to the blood.

However, by drinking milk, and due to the very makeup of the small proteins, hormones and amino acids found in milk, we stimulate the production of IGF in our bodies, resulting in increased blood levels of IGF-1.

This link between IGF-1 and cancers has been shown through population studies, which show a correlation between average milk consumption in the population and the occurrence of cancers. For instance there are 68.8 cases of breast cancer among every 100,000 woman in England and Wales compared with just 11.2 per 100, 000 in rural China where dairy is not included in the diet. Other research has compared blood samples from men diagnosed with prostate cancer with that of aged-matched controls.[1] Findings show that men with high IGF-1 levels had more than four times the risk of prostate cancer than men with the lowest scores.[5] Such research also shows an association between blood levels of IGF-1 and Prostate Specific Antigen (PSA), a prostatic marker which increases in cases of prostate cancer.[4]

The likely mechanism is that high IGF-1 levels keep prostate cells alive and growing regardless of whether the cells are normal or cancerous. The usual body mechanism gets rid of damaged cells by a process called apoptosis, or programmed cell death. IGF-1 seems to interfere with this mechanism.[6] By stimulating cell growth and preventing cells from dying off, IGF-1 keeps damaged cells alive, thus increasing the risk of cancer.

Other research though has shown that this anti-apoptic activity can be counterbalanced by the activity of insulin-like growth factor binding protein-3, the major binding protein. However, given the growing evidence for the link between high levels of IGF-1 and the increased risk certain cancers, one should be cautious about the amount of dairy in the diet. More alarming perhaps is that IGF-1 is easily available in the form of anti-ageing formulas that are widely used by athletes, body builders and those seeking the fountain of youth.

Of course, the variance of IGF-1 levels within the population is partly due to our genes and partly due to our diet. We can do little about the genes, but there is always something that we can do to improve our diet. Attention to childhood nutrition may provide a good long-term strategy for reducing cancer incidence, although there does seem to be some evidence that some of the nutritional markers associated with the increased risk of cancers are also associated with a decreased risk of insulin resistance and cardiovascular disease in later life.[2] Dietary intervention then should be treaded with caution and a balance sought. From current evidence though it seems that a prudent means of reducing the risk of contracting certain cancers would be to modify sources of dairy and re-balance the diet. Obtaining protein, vitamin D and minerals from alternative food sources such as fish, seeds, nuts and beans before reducing the intake of milk and dairy would be a good solution.

References

1. Holmes MD, Pollak MN and Hankinson SE. Lifestyle Correlates of Plasma Insulin-like Growth Factor 1 and Insulin-like Growth Factor Binding Protein 3 Concentrations. Cancer Epidemiology Biomarkers & Prevention. 11: 862-867. 2002.
2. Smith DG, Gunnell D and Holly J. Cancer and insulin-like growth factor-1. BMJ. 321: 847-948. 2000.
3. Holly JMP, Gunnell DJ and Smith GD. Growth hormone, IGF-1 and cancer. Less intervention to avoid cancer? More intervention to prevent cancer? Journal of Endocrinology. 162: 321-330. 1999.
4. Plant J. Prostrate Cancer - Understand, Prevent and Overcome. Cygnus Books. 2004.
5. Chan JM, Stampfer MJ, Giovannucci E, Gann PH, Ma J, Wilkinson P, Hennekens CH and Pollak M. Plasma Insulin-Like Growth Factor-I and Prostate Cancer Risk: A Prospective Study. Science. 279: 563-566. 1998.
6. Moschos SJ and Mantzoros CS. The Role of the IGF System in Cancer: From Basic to Clinical Studies and Clinical Applications. Oncology. 63: 327-332. 2002.