Senior author John Witte, from the Department of Urology, the Department of Epidemiology and Biostatistics, and the Institute for Human Genetics, Helen Diller Family Comprehensive Cancer Center, at UCSF, and colleagues, describe how they arrived at this conclusion in a paper published on 23 November in the online journal PLoS ONE.
The researchers embarked on the study because although established, the link between meat consumption and prostate cancer was not clear, and they wondered if this inconsistency reflects an effect whereby different types of tumors are linked to different types of meat preparation, due to different cancer-causing compounds, or carcinogens.
For their case-control study, between 2001 and 2004 they enrolled 470 men with aggressive prostate cancer and 512 matched controls who did not have prostate cancer. All the men had completed questionnaires that enabled the researchers to assess not only their meat intake for the previous 12 months, but also what type of meat and how it had been prepared, including "doneness level" from rare to well-done. The participants were recruited from major clinics and hospitals in Cleveland, Ohio.
The researchers used the National Cancer Institute's CHARRED database, which contains the mutagen content for each type of meat by cooking method and doneness. This data, together with the intake quantities given by the respondents, meant they could estimate participants' consumption levels of chemicals that have the potential to transform into cancer-causing compounds or carcinogens, such as heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs).
Then, using statistical tools, they analyzed the assembled data to look for associations "between overall and grilled meat consumption, doneness level, ensuing carcinogens and aggressive prostate cancer".
They found that:
- Higher consumption of any ground beef or processed meats was positively linked with aggressive prostate cancer, with ground beef showing the strongest association.
- The main driver of this link was intake of grilled or barbecued meat, with more well-done meat tied to a higher risk of aggressive prostate cancer.
- Men who ate high levels of well or very well cooked ground beef had twice the odds of developing aggressive prostate cancer compared to men who ate none. Low consumption raised the odds to 1.5.
- In contrast, no such link was found between consumption of rare or medium cooked ground beef and aggressive prostate cancer.
- Looking at the potential carcinogens produced by cooking meat at high temperatures, they detected an increased risk of aggressive prostate cancer tied to MelQx and DiMelQx, such that comparing the top 25% of intake with the lowest 25% of intake, the odds were 1.69 for MelQx and 1.53 for DiMelQx.
"Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are chemicals formed when muscle meat such as beef, pork, fish or chicken are cooked by high temperature methods such as pan frying or cooking over an open flame."
For instance, cooking meat on an open flame causes the fat and juices to drip into the fire, this produces the PAHs, and they get coated back onto the meat when it is licked by the flames.
The researchers conclude their findings show that high consumption of meat, especially grilled meat, and well or very well done red meat in particular, is positively linked with an increased risk of aggressive prostate cancer.
"Although certain mutagenic compounds, such as MelQx and DiMelQx, may play a role in this process, other molecules may also be involved and further studies are required to better characterize the potential role of these compounds in prostate carcinogenesis and to see whether these compounds may be targeted for chemoprevention of prostate cancer," they write.
Grants from the National Institutes of Health helped pay for the study.