October 19, 2010 — Drinking coffee is associated with a 36% reduction in the risk for cancer of the oral cavity and pharynx, according to Italian investigators who performed a meta-analysis of observational studies.
These findings echo those published earlier this year by the same group of researchers, and reported by Medscape Medical News at that time. However, the scope of the new study is larger and includes other aerodigestive tract cancers, including those of the esophagus.
The researchers did not find any association between coffee drinking and the risk for laryngeal and esophageal cancers.
Just how many cups a day is protective against oral and pharyngeal cancer could not be precisely determined from the analysis, say the investigators, led by Federica Turati, MD, from the Istituto di Ricerche Farmacologiche in Milan, Italy.
The meta-analysis concluded that the relative risk for cancer of the oral cavity and pharynx was 0.64 (95% confidence interval [CI], 0.51 - 0.80) for "highest" vs "lowest" coffee drinking. The analysis involved 2633 cases of these cancers, which came from 1 cohort and 8 case–control studies.
The authors point out that they could not assess the relation of cancer risk to the number of cups of coffee because the original studies used a variety of ways to quantify intake.
Nevertheless, "a favorable effect of coffee at moderate/high doses is suggested" by the studies included in the analysis, most of which compared drinkers of 3 or more cups to drinkers of less than a cup a day, they write.
So what is the biological explanation for the effect?
"There are no definite biological mechanisms of the potential favorable role of coffee on [oral cavity and pharynx] cancer," the authors write in their paper, which was published online October 13 in the Annals of Oncology.
However, coffee has "many chemicals with antioxidant and antimutagenic activities," they say. The concentration of these chemicals varies, "depending on type of coffee power (Arabica or Robusta), roasting, and preparation," the authors add.
A number of compounds found in coffee, such as chlorogenic acids, cafestol, and kahweol, have been shown to reduce the genotoxicity of several carcinogens, they explain.
The authors also point out that coffee drinking has been inversely related to liver cirrhosis, liver cancer, endometrial cancer, and colorectal cancer.
The study has limitations, including the bugaboo of all observational studies — the possibility of confounders. However, the meta-analysis only included studies that reported risk estimates adjusted for smoking and alcohol intake, the 2 major risk factors for cancer of the oral cavity and pharynx. A "slightly stronger" inverse association might exist in smokers, they say, but it was "difficult to quantify."
In addition, the original studies did not detail the cup size, type of coffee, or brewing methods, the Italian authors note about other limitations.
Greater Risk Reduction Seen in US and Europe
The meta-analysis was needed because the results of epidemiologic studies to date on the subject are "scattered and largely inconclusive," say the authors.
The original studies in the analysis came from around the world, so the authors also analyzed risk according to region.
The relative risks were 0.61 (95% CI, 0.41 - 0.89) for European, 0.58 (95% CI, 0.36 - 0.94) for American, and 0.74 (95% CI, 0.48 - 1.15) for Asian studies. The fact that the inverse relation was stronger in the United States and Europe and weaker in Asia, where less coffee is consumed, was suggestive of a protective effect, note the authors.
The study authors were unable to compare coffee drinkers with nondrinkers.
In the various original studies, no information was available on human papillomavirus (HPV), which is related to oral and pharyngeal cancer. However, the authors write, "there is no reason to suppose that coffee consumption is associated with or modified by HPV infection."
The study was funded by the Italian Association for Cancer Research. The researchers have disclosed no relevant financial relationships.
Ann Oncol. Published online October 13, 2010. Abstract
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