Colorectal (colon) cancer is the most common type of cancer in the Western Countries. In the United States, there are a reported 140,000 people diagnosed with colon cancer, and about 50,000 of these will succumb to the disease.
Several factors may contribute to the development of colorectal cancer, including an existing presence of polyps, family history, and diet. As more research has been done, there is increasing evidence linking high iron intake with the development of colon
cancer. This theory has been developed on the basis of the epidemiological evidence showing an association between high meat intake and cancer of the colon and rectum.
One major animal study analyzed a possible correlation between unrealistically high concentrations of iron and cancer development. This study was specifically designed to test whether chronic exposure to high levels of iron fortification affects the free radical generation capacity of the luminal contents, mucosal lipid peroxidation and crypt cell proliferation.
In the study, rats were fed with 29mg/kg or 102 mg/kg of elemental iron over a span of six months. While there was no recorded increase in crypt cell proliferation rate in either the colon or cecum, there was an increase in free radical generating capacity in the colon and increased lipid peroxidation, particularly in the cecum. Initial results from a study conducted by the National Health and Nutrition Examination Survey, a prospective study of over 10,000 people in the United States, showed that men who had developed colon cancer over the past 10 years had significantly higher levels of transferrin saturation (excessive amounts of iron present in the blood).
The role of iron in colon cancer
Several studies and investigations over the past decades have shown iron has the ability to favor neoplastic (abnormal cell) growth. Iron itself is carcinogenic due to its catalytic effect on the formation of hydroxyl radicals, suppression of the activity to host defense cells and promotion of cancer cell multiplication. In humans, and even in animals, primary neoplasm (tumor development) may develop in the body where excessive iron deposits are found. This part of the body may attempt to withhold iron deposits from cancer cells in newly formed ferritin (a protein that stores iron and releases it in a controlled fashion. In humans, ferritin acts as a buffer against iron deficiency and iron overload). The host will then endeavor to withdraw the metal from cancer cells via macrophage synthesis of nitric oxide.
What do the experts say?
Red meat: red meat contains what is called heme iron. People who eat high amounts of red meat have higher rates of colon cancer and lung cancer, as opposed to individuals who avoid red meat.
Tumour cells and bacteria: both rely on iron to grow. When iron is added to neoplastic cells, they tend to grow at a much faster rate. In 1988, several studies began to surface showing the iron was indeed a risk in common forms of cancers including colon, lung, and breast cancer. A study in the New England Journal of Medicine (Oct 1988) by Dr. Richard Stevens showed that as iron saturation levels increase, cancer rates go up.
Estrogen connection: Karen Collin, a dietitian and nutritionist for the American Institute for Cancer Research, wrote an article showing that heme iron may interacts with estrogen in promoting hormone related cancer. She also indicates that heme iron may damage the lining of the colon, later leading to colon cancer.
External factors leading to colon cancer: in Exogenous Factors in Colonic Carcinogenesis, 2003, W. Scheppach and M. Scheurlen state that “iron is directly linked to an increased risk of colorectal cancer”, and:
– high dietary iron intake will lead to a high availability of iron in the gut lumen – in fresh red meat, iron is bound mostly to myoglobin which is preferentially absorbed by the human body
So, while iron is an important mineral necessary for our blood cells to function properly, it’s important to understand that both iron deficiency and iron overload can pose serious health risks.