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, such as DiMeIQx (2-amino-3,4,8-dimethylimidazo(4,5-f)quinoxaline).
Overall, study participants in the top 20% for red-meat intake were 79% more likely than those in the bottom 20% to develop esophageal squamous cell carcinoma.
Meanwhile, the risk of gastric cardia cancer was elevated among men and women with the highest estimated intake of heterocyclic amines (HCAs), which form when meat is cooked using high-temperature methods.
The findings, reported in the November issue of the American Journal of Gastroenterology, add to what has been an uncertain body of evidence on the positive association 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 case-control studies, not prospective trials, explained Dr. Amanda J. Cross, a researcher at the U.S. National Cancer Institute who led the new study.
In addition, earlier research didn’t really examine meat intake and different subtypes of esophageal and stomach cancers. That is important, Dr. Cross told Reuters Health, because the different subtypes seem to have different risk factors.
So for their study, Dr. 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 SCC; that included 28 cases among the bottom 20% for red-meat intake, and 69 cases in the top 20%.
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% more likely than those with the lowest intake to develop SCC of the esophagus.
Red meat itself wasn’t associated with gastric cardia cancer. But for one type of HCA, known as DiMelQx, men and women in the top 20% for intake had a 44% higher risk of gastric cardia cancer than those in the bottom 20%.
Red meat wasn’t clearly linked to esophageal adenocarcinoma or to non-cardia stomach cancers.
The different findings for different cancer subtypes are “not hugely surprising,” Dr. 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’s somewhat surprising, Dr. Cross said, that none of the HCA compounds the researchers assessed was related to esophageal SCC, 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, Dr. Cross said, is that further large, prospective studies are needed to see whether the relationship between red meat and the two cancers is real.