NEW YORK (Reuters Health) - Red-meat lovers may have a greater likelihood of developing certain cancers of the throat and stomach than people who limit their intake of steaks and hamburgers, a new study suggests.
Researchers found that among nearly 500,000 older U.S. adults followed for a decade, only a small number developed cancers of the esophagus or stomach. However, the risks were relatively greater among those who ate a lot of red meat, or certain compounds generated from cooking meat.
Overall, study participants in the top 20 percent for red-meat intake were 79 percent more likely than those in the bottom 20 percent to develop esophageal squamous cell carcinoma — a cancer that arises in the lining of the upper part of the esophagus.
Meanwhile, the risk of a type of cancer in the upper portion of the stomach near the esophagus (gastric cardia) was elevated among men and women with the highest estimated intake of one form of heterocyclic amine (HCA). HCAs are compounds that form when meat is cooked using high-temperature methods, such as grilling over an open flame; they have been found to cause cancer in lab animals.
The findings, reported in the American Journal of Gastroenterology, do not prove that red meat promotes the two cancers, the researchers emphasize.
But the results add to what has been an uncertain body of evidence on the link between red meat and esophageal and stomach cancers.
A 2007 research review by the World Cancer Research Fund and American Institute for Cancer Research, both non-profit groups, concluded that red and processed meats were associated with a “limited suggestive increased risk” of esophageal cancer.
The report also said there was a similar level of evidence for a link between processed meats and stomach cancer, and insufficient data on whether red meat intake is connected to the cancer at all.
However, most of the studies considered in the report were so-called case-control studies, where researchers ask patients with a given disease about their past lifestyle habits and other health factors, then compare them to a group of healthy individuals.
That type of study design can offer only limited evidence about whether a particular exposure — like red meat in the diet — is related to a disease risk, explained Dr. Amanda J. Cross, a researcher at the U.S. National Cancer Institute who led the new study.
Studies with prospective designs, which follow initially healthy people over time, provide stronger evidence.
In addition, most earlier research did not look at meat intake and different subtypes of esophageal and stomach cancers. That is important, Cross told Reuters Health, because the different subtypes seem to have different risk factors.
So for their study, Cross and her colleagues prospectively followed 494,979 U.S. adults ages 50 to 71 over roughly 10 years. At the outset, participants completed detailed questionnaires on their diets — including the methods they typically used for cooking meat, and the usual level of “doneness” they preferred — as well as other lifestyle factors.
Over the next decade, 215 study participants developed esophageal squamous cell carcinoma; that included 28 cases among the bottom 20 percent for red-meat intake, and 69 cases in the top 20 percent.
Another 454 men and women were diagnosed with gastric cardia cancer. There were 57 cases among participants with the lowest red-meat intake, and 113 in the group with the highest intake.
When the researchers accounted for other factors — like age, weight, smoking and reported exercise habits — participants who ate the most red meat were 79 percent more likely than those with the lowest intake to develop squamous cell carcinoma of the esophagus.
Red meat itself was not associated with gastric cardia cancer. But for one type of HCA, known as DiMelQx, men and women in the top 20 percent for intake had a 44 percent higher risk of gastric cardia cancer than those in the bottom 20 percent.
Red meat was not clearly linked to esophageal adenocarcinoma — a cancer that arises in glandular cells in the lower esophagus, and is the more common form seen in the U.S. — or to cancers in other parts of the stomach (non-cardia stomach cancers).
The different findings for different cancer subtypes are “not hugely surprising,” Cross said, since they may differ in their underlying causes. She noted, for instance, that smoking and heavy drinking appear to be stronger risk factors for esophageal squamous cell cancer compared with adenocarcinoma, while obesity seems to be a greater factor in adenocarcinoma risk.
It is somewhat surprising, Cross said, that none of the HCA compounds the researchers assessed was related to esophageal squamous cell cancer, even though red-meat intake was. It is thought that, if red meat does contribute to the cancer, HCA exposure would be one reason why.
The bottom line, Cross said, is that further large, prospective studies are needed to see whether the relationship between red meat and the two cancers is real. She pointed out, though, that many health authorities already recommend that people limit their consumption of red and processed meats for the sake of their overall health.
The American Cancer Society estimates that about 21,000 cases of stomach cancer and 16,640 cases of esophageal cancer will be diagnosed in 2010.
SOURCE: link.reuters.com/vuv93q American Journal of Gastroenterology, online October 26, 2010.