The September 5, 2006 issue of the Annals of Internal Medicine reports on a NIH Conference on the use of multivitamins/mineral supplements (MVMs) and chronic disease prevention.
...the present evidence is insufficient to recommend either for or against the use of MVMs by the American public to prevent chronic disease."
A major reason for the panel's inability to make a firm recommendation is the lack of randomized clinical trials.However, the panel interestingly also states that "multivitamin trials are unlikely to lead to generalizable knowledge".
This is because a distinction between the effects of the individual components is unlikely to be made for several reasons including 1)the placebo group is likely to take vitamins anyway, 2)a very large sample size would be required making funding and execution of the trial problematic and 3)results would be likely outdated as the composition of the commonly used MVMs tend to change. Further, there is reason to believe that some subgroups may benefit from a given component while another subgroup might be harmed.
So what are we hearing? We cannot say if MVMs should be taken by everyone to prevent chronic disease or cancer because of the lack of RCTs and it is unlikely that even if we could the related RCTs they probably would not answer the question anyway. Should we withhold judgment if there is no randomized trial directly addressing the issue? Are we unnecessarily limiting ourselves by punting every question if RCTs are not available? That does appear to be the modus operandi of the public health community and yet in that context there is justification for withholding judgment until the evidence is quite strong. To make policy decisions sound evidence is required. Individual physicians have to often make decisions with the data they have not the evidence they wished they had. Of course, physicians do not have to tell everyone what to do , just the patient on the other side of the desk.