Breast Cancer Treatment: Diet
Before we can get into detailed discussion of natural products proposed to help prevent cancer, we must first discuss some fundamental issues regarding the nature of medical evidence.
It is rather difficult to prove that taking a certain supplement will reduce the chance of developing cancer. One really needs enormous long-term, double-blind, placebo-controlled studies in which some people are given the supplement while others are given placebo. However, relatively few studies of this type have been performed.
For most supplements, the evidence that they help prevent cancer comes from observational studies, which are much less reliable. Observational studies have found that people who happen to take in high levels of certain vitamins in their diets develop a lower incidence of specific cancers. However, in such studies it is very difficult to rule out other factors that may play a role. For example, individuals who take vitamins may also exercise more, or take better care of themselves in other ways. Such confounding factors make the results of observational studies less reliable.
Although this may sound like a theoretical issue, it has very practical consequences. For example, based primarily on observational studies, hormone replacement therapy was promoted as a heart-protective treatment for post-menopausal women. However, when placebo-controlled studies were performed, hormone replacement therapy proved to increase the risk of heart disease.
It is now thought that apparent benefits of hormone replacement therapy were due to the fact that woman who used it belonged to a higher socioeconomic class than those who did not use it. (For a variety of reasons, some of which are obscure, higher income is associated with improved health.)
Only a few supplements have any evidence from double-blind trials to support their potential usefulness for cancer prevention, and even that evidence is weak. For all other supplements, supporting evidence is limited to observational studies, as well as preliminary evidence from animal and test tube studies.
However, it is important to keep in mind that most placebo-controlled and double-blinded studies are seeking to prove the efficacy of a single substance (like a particular drug, vitamin, substance or intervention), but it is often thought that the interaction among certain vitamins or of vitamins within diet (and not simply in an extrapolated pill form) is what makes it effective. So while many double-blind studies have not been "successful" this may be more a product of trying to prove a supplement's efficacy with an inadequate test.