Meat And Colorectal Cancer Risk: Scientists Suggest Potential Mechanisms

I don't really look for stuff that shows meat is bad for you, but I stumbled across this article then dug up some bits of research because it covered something I'd come across before.
This study showed that 3 things appeared to be carcinogenic in red meat & processed meats:
nitrate/nitrite
heterocyclic amines
heme iron

The first 2 are not new to me, but I hadn't heard that heme iron was a likely contender for being a cancer forming product. Animals produce heme iron, plants produce non-heme iron. You can overdose on heme iron, you can't from non-heme iron as the body regulates assimilation. That is old news, but hearing it could well be cancer causing was news to me.
I'll add the article below, but basically it appears to confirm that red meat & processed meat does increase your chances of colon cancer. I'll also add the abstract of the original research that inspired the article & an older bit of research about heme iron & it's effect on the body as well.

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The original article I read

Meat And Colorectal Cancer Risk: Scientists Suggest Potential Mechanisms
rate icon Featured Article
Main Category: Colorectal Cancer
Also Included In: Nutrition / Diet; Cancer / Oncology; GastroIntestinal / Gastroenterology
Article Date: 10 Mar 2010 - 9:00 PST


Scientists in the US who undertook a large study to investigate what biological mechanisms might be behind the already established link between colorectal cancer and consumption of red and processed meat, confirmed that such a link exists and suggested the main players are three compounds: heme iron, nitrate/nitrite, and heterocyclic amines.

You can read a paper on the research behind these findings in the published online first 9 March issue of Cancer Research. Most of the research team members, including corresponding author Dr Amanda J Cross, were from the Division of Cancer Epidemiology and Genetics, at the US National Cancer Institute (NCI) in Rockville, Maryland.

The authors noted that although the link between consumption of red and processed meat and colorectal cancer has been demonstrated in several studies, few have explored the underlying mechanisms.

Cross and colleagues undertook a large prospective study that counted colorectal cancer cases in a cohort of over 300,000 men and women who filled in detailed questionnaires about the types of meat they consumed and how it was cooked.

In their analysis they linked the questionnaire data to information kept in scientific databases about the levels of compounds present in meat cooked at different temperatures. The compounds they were interested in were heme iron, nitrate, nitrite and certain mutagens. (Mutagens are compounds that can alter DNA or other genetic material, thus increasing the rate of rogue cell production which can trigger cancer).

In their analysis the researchers arranged the cohort data in "quintiles". That is they grouped it into five bands: the bottom quintile contained the data on those who ate the least meat and the top quintile contained data on those who ate the most.

They then compared the hazard ratios (HR) of the top quintile with the bottom quintile: thus working out how much extra risk of developing colorectal cancer was represented in the 20 per cent of the cohort that ate the most meat compared to the 20 per cent that ate the least.

The results showed that:

* After 7 years of follow up, there were 2,719 cases of colorectal cancer in the cohort.

* Comparing the top quintile (the 20 per cent that ate the most meat) with the bottom quintile (the 20 per cent that ate the least meat) for both red and processed meat showed a significantly higher risk of developing colorectal cancer.

* The HR for red meat was 1.24 (24 per cent higher risk) and for processed meat it was 1.16 (16 per cent higher risk).

* The potential mechanisms for this that showed statistical significance were intakes of heme iron (HR 1.13), nitrate from processed meats (HR 1.16) and heterocyclic amines (HR 1.19).

* In general, the elevated risk was higher for rectal cancer than colon cancer, with the exception of two heterocyclic amines (MeIQx and DiMeIQx), which were only linked to colon cancer.

The researchers concluded that they found:

"A positive association for red and processed meat intake and colorectal cancer; heme iron, nitrate/nitrite, and heterocyclic amines from meat may explain these associations."

Studies have shown that cooking certain meats at high temperatures produces chemicals that are not present in meats that are uncooked.

Some of these chemicals, such as heterocyclic amines, form when muscle meat is cooked (eg from beef, pork, fowl and fish). HCAs are made when creatine (a chemical found in muscle tissue) combines with amino acids at high temperature.

According to the NCI, scientists have found 17 different heterocyclic amines in cooked muscle meat that may pose a cancer risk in humans.

"A Large Prospective Study of Meat Consumption and Colorectal Cancer Risk: An Investigation of Potential Mechanisms Underlying this Association.
Amanda J. Cross, Leah M. Ferrucci, Adam Risch, Barry I. Graubard, Mary H. Ward, Yikyung Park, Albert R. Hollenbeck, Arthur Schatzkin, and Rashmi Sinha.
Cancer Research, Published online first on March 9, 2010
DOI:10.1158/0008-5472.CAN-09-3929

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Abstract the article is based on

A Large Prospective Study of Meat Consumption and Colorectal Cancer Risk: An Investigation of Potential Mechanisms Underlying this Association
Amanda J. Cross1, Leah M. Ferrucci1, Adam Risch4, Barry I. Graubard2, Mary H. Ward3, Yikyung Park1, Albert R. Hollenbeck5, Arthur Schatzkin1 and Rashmi Sinha1

Authors' Affiliations: 1 Nutritional Epidemiology Branch, 2 Biostatistics Branch, and 3 Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, Rockville, Maryland; 4 Information Management Services, Inc., Silver Spring, Maryland; and 5 AARP, Washington, District of Columbia

Corresponding Author: Amanda J. Cross, 6120 Executive Boulevard, Rockville, MD 20852. Phone: 301-496-4378; Fax: 301-496-6829; E-mail: crossa@mail.nih.gov.

Although the relation between red and processed meat intake and colorectal cancer has been reported in several epidemiologic studies, very few investigated the potential mechanisms. This study examined multiple potential mechanisms in a large U.S. prospective cohort with a detailed questionnaire on meat type and meat cooking methods linked to databases for estimating intake of mutagens formed in meats cooked at high temperatures (heterocyclic amines, polycyclic aromatic hydrocarbons), heme iron, nitrate, and nitrite. During 7 years of follow-up, 2,719 colorectal cancer cases were ascertained from a cohort of 300,948 men and women. The hazard ratios (HR) and 95% confidence intervals (95% CI) comparing the fifth to the first quintile for both red (HR, 1.24; 95% CI, 1.09–1.42; Ptrend < 0.001) and processed meat (HR, 1.16; 95% CI, 1.01–1.32; Ptrend = 0.017) intakes indicated an elevated risk for colorectal cancer. The potential mechanisms for this relation include heme iron (HR, 1.13; 95% CI, 0.99–1.29; Ptrend = 0.022), nitrate from processed meats (HR, 1.16; 95% CI, 1.02–1.32; Ptrend = 0.001), and heterocyclic amine intake [HR, 1.19; 95% CI, 1.05–1.34; Ptrend < 0.001 for 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and HR, 1.17; 95% CI, 1.05–1.29; Ptrend <0.001 for 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (DiMeIQx)]. In general, the elevated risks were higher for rectal cancer than for colon cancer, with the exception of MeIQx and DiMeIQx, which were only associated with colon cancer. In conclusion, we found a positive association for red and processed meat intake and colorectal cancer; heme iron, nitrate/nitrite, and heterocyclic amines from meat may explain these associations. Cancer Res; 70(6); 2406–14

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Another heme study

Haem, not Protein or Inorganic Iron, Is Responsible for Endogenous Intestinal N-Nitrosation Arising from Red Meat
Amanda Jane Cross, Jim R. A. Pollock and Sheila Anne Bingham1

Medical Research Council, Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Cambridge CB2 2XY [A. J. C., S. A. B.], and Pollock and Pool Ltd., Reading RG5 4DX [J. R. A. P.], United Kingdom

Many N-nitroso compounds (NOC) are carcinogens. In this controlled study of 21 healthy male volunteers, levels of NOC on a high (420 grams) red meat diet were significantly greater (P = 0.001) than on a low (60 grams) meat diet but not significantly greater when an equivalent amount of vegetable protein was fed. An 8-mg supplement of haem iron also increased fecal NOC (P = 0.006) compared with the low meat diet, but 35-mg ferrous iron had no effect. Endogenous N-nitrosation, arising from ingestion of haem but not inorganic iron or protein, may account for the increased risk associated with red meat consumption in colorectal cancer.