Much of the promise for cancer prevention comes from observational research studies. “Prevention trials test new approaches, such as medications, vitamins, or other supplements, that doctors believe may lower the risk of developing a certain type of cancer. Most prevention trials are conducted with healthy people who have not had cancer. Some trials are conducted with people who have had cancer and want to prevent recurrence (return of cancer), or reduce the chance of developing a new type of cancer.” - National Cancer Institute (NCI)
Examples of prevention trials include the benefits of green tea and foods containing polyphenols.
While we wait for this evidence, the safe thing to do is practice good health habits. However, we know how frustrating it is to read conflicting stories on what to eat or do to prevent cancer.
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These prevention studies are called epidemiological studies and are best suited to exploring links between modifiable lifestyle factors or environmental exposures and specific cancers.
Once this link is found in epidemiology studies, researchers move to interventional clinical trials to determine whether these links can be modified by some intervention. (add or subtract some behavior like food, exercise, vitamins).
In typical clinical trials, half the participants do one thing (i.e., the experimental or interventional group) and the other half of participants do nothing different than usual (e.g., the control group).
Evidence is now emerging from randomized controlled trials designed to test whether interventions suggested by the epidemiologic studies, as well as leads based on laboratory research, result in reduced cancer incidence and mortality.
