My first reaction to such flip-flops is that we should not be too surprised. After all, such about-faces are par for the course in nutritional research.
Who amongst us has not tired of hearing about the alleged benefits of a Mediterranean diet, or a Vegan diet, or a low-fat diet, or a low-carbohydrate diet, or a low-protein diet?
Psychologists, as well as physicians, have long known that a “medicine” can be helpful even if it contains no active ingredient and this now includes vitamins. This is the placebo effect according to which a patient who received just a sugar pill often evinces a remarkable recovery.
The Placebo Effect
Although doctors used to laugh amongst themselves about administering placebos, the joke is on them for several reasons. First, the placebo effect can be quite strong (1). Second it can be “real” in the sense that it produces physiological effects that can be prevented by experimental administration of opiate blockers or other drugs. Third, most active medicines are accompanied by a placebo effect that must be controlled for in drug research. Fourth, although drug manufacturers don't like this to be widely known, the placebo effect of a drug is often as big, or bigger, than that of the active ingredient. Fifth, placebos do not have adverse side effects as many prescription drugs do.
All of these issues were thoroughly aired in connection with anti-depressant drugs.
A 2002 study analyzed FDA data on the 6 most widely-prescribed antidepressants (1). It found that placebos had about 80% as much effect as the drugs themselves, suggesting that “the pharmacological effects of antidepressants are clinically negligible.” A large dose had no more effect than a smaller one.
A widely-read 2010 JAMA article (2) went so far as to say that most people taking anti-depressant drugs do no better than if they had received a sugar pill. Needless to say, these papers incited a great deal of controversy about the size of placebo effects and whether they apply to objective measures of illness as opposed to self-reports used in studies of depression.
The Placebo Effect and Vitamins
In contrast to many FDA approved drugs, vitamins would appear to be generally harmless. If taking any pill can unlock a placebo effect, then users of vitamin supplements might prove less vulnerable to common illnesses.
If vitamins are considered as placebos, they could potentially have beneficial effects for general health and longevity. When researchers first investigated the health impact of vitamins, they did so from the perspective of antioxidant properties of vitamin C but their scientific rationale is unimportant. What matters is the results. Unfortunately, there is no evidence that Vitamin C prevents colds in the general population (although it may reduce the cold's duration in some populations such as endurance athletes 3).
Whatever about coping with colds, perhaps vitamins contribute to general health, making people less vulnerable to aging. If this were true, then users of multivitamins would enjoy greater longevity. Once again, the evidence could not be more disappointing. Vitamin users live exactly as long as nonusers according to a meta-analysis combining many different studies (4). When the researchers looked at the better-conducted studies, they found that vitamin users lived shorter lives.
Why do Vitamins not Yield a Placebo Benefit?
So we can be fairly confident that vitamin users are not healthier, or more long-lived, than others. This means that vitamins do not yield a placebo benefit. Why not?
There are a limited number of plausible reasons. Perhaps vitamins are taken mostly to counteract dietary deficiencies and without any expectation that they will minimize infections such as the common cold. There is no placebo effect because there is no expectation that any specific health problem will improve.
Another obvious possibility is that placebos don't work if they are self-administered. In other words, the placebo effect is an inherently social phenomenon with a child's sore spot relieved by its mother's kiss, or a patient's illness improved by doctor-prescribed medicine. The point is that another person takes responsibility for the problem.
So vitamins may provide clues about the placebo effect even if they don't produce one.
2 Fournier, J. C., et al. (2010). Antidepressant drug effects and depression severity. JAMA, 303, 47-53.
3 Hamila, H., and Chalker, E. (2012). Vitamin C for preventing and treating the common cold. The Cochrane Library. Http://www.thecochranelibrary.com/view/o/index.html
4 Pagannini-Hill, A., Cawas, C. H., and Corrada, M. M. (2015). Antioxidant vitamin intake and mortality: The Leisure World Cohort Study. American Journal of Epidemiology, 181, 120-126.