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Vlees en de kans op darmkanker*
Uit een studie onder 300.000 personen blijkt dat het regelmatig eten van vlees de kans op darmkanker duidelijk kan verhogen. Het blijkt vooral het (heem)ijzer, de nitraten en nitrieten en de heterocyclische aminen te zijn die hiervoor verantwoordelijk zijn. (Eiwitten in het vlees vormen bij (te) hoge temperaturen wel 17 verschillende heterocyclische aminen, HCA's) Zij die het meeste vlees aten in de studie bleken 24% meer kans te hebben op darmkanker dan zij die het minste vlees aten. Voor bewerkt vlees was dat percentage 16%. Heemijzer bleek 13% meer kans te geven, nitraten en nitrieten 16% en de heterocyclische aminen 19%.
Meat And Colorectal Cancer Risk: Scientists Suggest Potential Mechanisms
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 in 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, DOI:10.1158/0008-5472.CAN-09-3929
(Mei 2010)


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