TCS Daily

Coffee Causes Cancer! Oops, This Just In! Coffee Prevents Cancer!

By Elizabeth M. Whelan - February 25, 2005 12:00 AM

Recent headlines claimed that drinking coffee can reduce our risk of liver cancer. A study of some 90,000 Japanese found that people who drank coffee daily or nearly every day had half the liver cancer risk of those who never drank coffee. The study was published in the Journal of the National Cancer Institute.

As I pondered these headlines, I recalled a morning in 1981 when I turned on the Today show at 7 a.m. and was greeted with grim news: drinking coffee caused pancreatic cancer. The messenger delivering this news right at the top of the show was Dr. Brian MacMahon, a professor of epidemiology at Harvard (a former professor of mine) who had just published a study "Coffee and Cancer of the Pancreas" in the New England Journal of Medicine. Dr. MacMahon opined that drinking even three cups of coffee a day increased the risk of pancreatic cancer threefold -- and that coffee may have caused nearly half the pancreatic cancers in the United States.


Years later, it became evident that other studies did not confirm a causal link between coffee and pancreatic cancer -- and by year 2000, the American Cancer Society formally dismissed any causal link here.


Was the MacMahon study poorly done, resulting in inaccurate and misleading results? Not necessarily.


What this example demonstrates is that one study does not a conclusion make. Science is a process of exploration, requiring examination, reassessment, and replication. Only when there exists a large, consistent body of evidence demonstrating that some factor is linked to disease -- whether it has a harmful or protective effect -- can a credible association be established. Is there now such a credible association established for coffee protecting us from liver cancer? Should we all step up our coffee consumption just in case?


Clearly the answer to both questions is "no." Consumers must be constantly skeptical of studies linking variable A with disease B, whether the news is potentially good (as was the coffee/liver cancer link) or just plain scary (many people in the early 1980s made a concerted effort to wean themselves from their coffee habit after the coffee/pancreatic cancer headlines appeared).


It may be unrealistic to ask the media to refrain from reporting isolated findings -- particularly when those findings appear in prestigious medical journals. But surely journalists could put such reports in context by adding a commentary noting that the findings reported are from one study, that they have yet to be confirmed in other research, and that there is no reason for consumers to modify their behavior based on one report -- no matter where it was published.


Without such a clarification, consumers will understandably become numb over the constant warnings and "new findings," confusing purely hypothetical disease causes with well-established ones.


Dr. Elizabeth M. Whelan is president of the American Council on Science and Health (


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