Drinking two cups of strong coffee a day may protect habitual cigarette smokers from developing advanced colon cancer, according to a population-based study of Singapore Chinese, funded by the National Cancer Institute and conducted by researchers from the University of Minnesota. The study was published in the March-April edition of the Nutrition and Cancer journal (U.K.) and appeared online Jan. 26, 2010. This study, however, should not be construed to show that people can continue smoking tobacco and avoid disease if they drink coffee, caution the authors.
“Singapore Chinese prepare coffee in a way that likely preserves the putative chemoprotectants, cafestol and kahweol, that have been the primary focus of basic science investigations of coffee and cancer prevention,” said Sabrina Peterson, Ph.D., assistant professor of Foods and Health, Department of Food Science and Nutrition, University of Minnesota.
Singaporeans primarily drink coffee made by boiling ground dark roasted coffee beans with water in a pot, letting the grounds settle, and then pouring the liquid through muslin cloth filters to strain. Due to significant trapping of cafestol and kahweol found in the cloth filters, Peterson’s team assumed that these two compounds are present in significant amounts in common Singapore coffee, and may protect frequent coffee drinkers against the development of advanced colorectal cancer.
Colorectal cancer is the third most common malignant cancer worldwide. There has been little improvement in survival for patients with advanced stage disease, despite advances in surgical techniques and therapy. While younger adults can develop colorectal cancer, the chances of developing colorectal cancer increase markedly after age 50. More than 90 percent of people diagnosed with colorectal cancer are older than 50.
Peterson and her colleagues reviewed health information on over 60,000 middle-aged or older Chinese men and women who were enrolled in the Singapore Chinese Health Study. They investigated if coffee consumption was associated with decreased risk of colorectal cancer in frequent cigarette smokers and if the stage of disease was modified by the association.
To achieve their goal, the team assessed baseline dietary exposures through in-person interviews, using a food frequency questionnaire, followed by blood collection and lipid measurement. The relationship between coffee consumption and colorectal cancer risk was assessed through statistical analysis that compared distributions of selected variables across different levels of coffee consumption, as well as factors such as cigarette smoking (never, light, heavy), and the age smokers started.
Of the 60,000 study participants, 961 colorectal cancer cases occurred during the first 12 years of study follow up. Among the 961 colorectal cancer cases, 591 were colon and 370 were rectal cancer cases.
The scientists noted that among a subset of ever-smokers (at least one cigarette each day for one year), the consumption of two or more cups of coffee a day was associated with a statistically significant reduction in the risk of advanced colon cancer (Dukes C and D, or stages III and IV), but not for localized cancer (Dukes A and B, or stages I and II), which is usually early stage disease.
A similar analysis for rectal cancer found no association between coffee intake and the risk of rectal cancer in all subjects or those stratified by smoking status. Coffee drinking was not associated with either localized or advanced stages of rectal cancer.
Coffee May Mitigate the Toxicity of Cigarette Smoking
The method of coffee preparation can significantly influence the levels of potentially chemoprotective components in coffee. Instant, filtered, and percolated coffee have negligible amounts of cafestol and kahweol; whereas espresso has intermediate amounts and Turkish and Scandinavian-type boiled coffee—the the method used by Singaporeans—have large amounts.
Further, coffee and its components, specifically cafestol and kahweol, have been found to mitigate the toxicity of heterocyclic aromatic amines (HAA, sometimes referred to as simply heterocyclic amines, HCA), compounds that have been implicated in the development of colorectal cancer in animal studies. Meats cooked at high temperatures are typically considered primary HAA sources, and the main source of HAA exposure in North American or European Whites, according to current epidemiologic data.
But studies by collaborators at the University of Minnesota and New York State Department of Health found that cigarette smoking, not diet, was a major source of HAA exposure in Chinese people.
In light of the predominance of coffee and colorectal cancer data from studies of Caucasians, and identification of cigarette smoking as a major source of HAA in Chinese, the team investigated the coffee and colorectal cancer association of smokers enrolled in the Singapore study.
They found ever-smokers only had a positive association between coffee intake and protection against advanced colon cancer.
Coffee and Colon Cancer Association Strengths and Limitations
There are several strengths to this study, according to the scientists. Information on coffee consumption and other dietary and lifestyle factors were collected prior to cancer diagnosis, thus ruling out the possibility of recall bias and reverse causality, especially when there was a strong coffee and colon cancer association with longer, rather than with shorter, follow-up. Subgroup analyses in ever-smokers were biologically driven given the recent identification of cigarette smoking as a more likely source of HAA than diet in Chinese people. Finally, the study population is genetically homogeneous and free of potential confounders that may be widely studied in various White populations.
One limitation of the study was the relatively small sample sizes in subgroup analysis. Therefore, the findings of this study should be interpreted with caution and need to be confirmed in future studies, according to the scientists.
In addition, future studies that not only assess the amounts of coffee consumed, but also the type of coffee, the method of preparation of the coffee, and contents of cafestol and kahweol are warranted to shed light on the role of coffee in the protection against colon cancer.
Reference: Peterson S et al., Coffee Intake and Risk of Colorectal Cancer Among Chinese in Singapore: The Singapore Chinese Health Study. Nutrition and Cancer, United Kingdom, March-April 2010, DOI: 10.1080/01635580903191528.Print This Post