That flip-flop from such a prestigious institution contributed greatly to the public distrust of the science of epidemiology and the widespread perception that “one day they say something is good for us and the next day they say it is bad.”
Today's news seems pretty clear. Men who drank the most coffee, six cups or more daily, had a 60 percent lower risk of developing lethal prostate cancer — and 20 percent lower risk of developing any form of the disease, according to the study published in the online edition of the Journal of the National Cancer Institute.
Even lighter consumption — up to three cups daily — was associated with a 30 percent lower risk of lethal prostate cancer.
Because the results were the same whether the coffee was regular or decaffeinated, it's not the jolt of the java that provided the protection, researchers said. Instead, the benefit is likely linked to other compounds in coffee that act as antioxidants, reduce inflammation and regulate insulin.
The new research studied nearly 50,000 U.S. men who reported their coffee consumption every four years from 1986 to 2008. It backs up previous studies that found coffee consumption was associated with lower risk of a wide range of diseases including Parkinson's, type 2 diabetes and liver cancer.
Taken together, they support the notion that a wicked coffee habit actually may be good for your health.
Complex and changing So, what happened in the last three decades? For one thing, the science of epidemiology — the study of health-related events or disease, including public health research — has matured a lot since then and researchers have learned not to make too much of findings that may be later disproved.
It is never easy to study human beings who live in a complex, ever-changing environment. Humans are not lab rats where everything can be controlled. Still, even with the limitations, some kinds of epidemiological studies provide far better evidence than others.
According to Dr. Meir Stampfer, now the chief of epidemiology at Harvard School of Public Health and a co-author of today’s coffee paper "the main difference between (the new study) and the discredited pancreas finding is that ours is prospective, so there is no issue with recall bias."
What does that mean? The first pancreas cancer trial was what is called a “case control trial.” The scientists questioned 369 patients with pancreatic cancer and asked them about their dietary and other habits. Then they asked 644 healthy people the same question. The use of coffee jumped out so much that the authors came to the frightening conclusion that coffee use might account for a substantial proportion of the cases of this disease in the United States.
It sounds scary, but “recall bias” can affect the outcome of a study. People with a terrible disease like pancreatic cancer often wonder why they got it, even though there can be no answer. If they learn that the scientists are interested in coffee as a possibility, they are far more to remember every cup they ever drank than the normal controls. That's where the bias occurs.
The current research is called a prospective trial, which follows participants over a period of time. For the course of the trial, the volunteers have been filling out forms about their dietary and other habits, includin PU POST /post-create.do HTTP/1.1
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