Fans of magic bullets were cheered by this week's headlines proclaiming that a daily multivitamin supplement can cut our cancer risk.
Not so fast, people! Although the study appears to be methodologically sound, its results may have been skewed by several factors, including the selection of its participants and its source of funding.
But first, the study: In a large clinical trial of nearly 14,641 older male doctors who were followed for 11 years, that those taking a daily multivitamin experienced 8% fewer cancers than the subjects taking placebo (dummy) pills. This was a randomized, double-blinded, placebo-controlled clinical trial, the kind of study considered the most reliable.
And yet, for a number of reasons its results should be interpreted with caution.
First, past multivitamin studies have yielded mixed results and this may be just one more in a long string of contradictory investigations.
In the Cancer Prevention Study II, which followed up more than 1 million U.S. adults beginning in the early 1980s, multivitamin use was not associated with cancer mortality (1). The Women’s Health Initiative found that multivitamins had little or no relationship with the risk of breast, colon, or other cancers in more than 160 000 women followed up for a mean of 8 years (2).
More damning still, among 35 000 Swedish women, multivitamin use was associated with a 19% increased risk of breast cancer during a 10-year period compared with women not using these vitamins (3).
Second, the numbers aren’t as exciting as the headlines suggest. A reduction in overall cancer risk of 8% is actually pretty paltry when compared with the 35% reduction in the incidence of the most common cancers that accrues from eating a healthy diet, exercising and having a healthy weight — preventability estimates the World Cancer Research Fund never tires of repeating. Smoking accounts for roughly another 30% of cancers. Put together, these healthy lifestyle habits are substantially more cancer-protective than the modest benefits of a multi revealed by this study.
Moreover, the study found no benefits of multivitamins in prostate cancer, the most common cancer among the participants in the study. It did find a 12% reduction in the risk of death from cancer, but those findings were not strong enough to be statistically significant. (In fact, even the 8% finding was only just statstically significant with its p-value of 0.04. Statisticians typically say a result is significant if its p-value is less than 0.05.)
Third, no women or younger men participated in this trial, so its findings apply to perhaps a quarter of the population, probably less. Moreover, the men studied here – all of them retired doctors – are not representative even of older males: very few of them smoked, most ate a healthy diet and were generally in good health. (In less-well-nourished populations a multivitamin supplement might actually bring about greater benefit – but that’s only a hypothesis which this study does not address.)
Finally, the study was supported by chemicals company BASF (who manufactures vitamins), while pharmaceuticals giant Pfizer provided the multivitamins and placebo pills used in the study, in addition to grants from the National Institutes of Health.
Understandably, both companies would have been keen for a positive outcome to this study. Indeed, a Pfizer spokesman noted that the company is “very pleased” that the researchers chose their multi for the study.
Of course, the study’s authors insist that the sponsors did not influence the study design, data analysis or manuscript preparation. Nonetheless, it’s been shown repeatedly that the source of a scientific study’s funding can significantly influence its outcome.
Thus, drug research sponsored by pharmaceutical companies is considerably more likely to favor the drug under consideration than studies sponsored by government grants or charitable organizations (4). Similarly, nutrition research financed by the food industry is more likely to end up favoring the food under consideration than independently funded research (5). So when I see a study shining a positive light on its sponsors’ products, I’m wary.
My final misgiving is that casual readers of the study (and I’m sure some didn’t read past the headlines before rushing to the drug store) will conclude that healthy eating is a waste of time and all they need to do is take a multivitamin supplement. As the product’s name states, it should be a supplemental measure to an already healthy diet and lifestyle, not a substitute for it; but for many, this is just irksome small print.
I for one remain convinced that a diet that’s packed with fresh, nutrient-dense foods and free from toxins, unhealthy additives and processed junk provides many more cancer-fighting nutrients than the best-quality supplement ever will.
Sure – take a multi if it makes you feel better; it may even help out on the days when you don’t have the time to eat a decent meal. But don’t expect a supplement to provide the quality, quantity and synergies of fresh foods brimming with vitamins, minerals, healthy fats, fiber, bioactive plant chemicals and vital energy.
(Apologies to my regular readers that the recent series of daily anti-cancer recipes was recently disrupted by technical problems and this news story; I'll be back soon with a recipe so nutritious it would put any multivitamin to shame!)
(1) Watkins ML, Erickson JD, Thun MJ, Mulinare J, Heath CW Jr. Multivitamin use and mortality in a large prospective study. Am J Epidemiol. 2000;152(2):149-162
(2) Neuhouser ML, Wassertheil-Smoller S, Thomson C, et al. Multivitamin use and risk of cancer and cardiovascular disease in the Women’s Health Initiative cohorts. Arch Intern Med. 2009;169(3):294-304
(3) Larsson SC, Akesson A, Bergkvist L, Wolk A. Multivitamin use and breast cancer incidence in a prospective cohort of Swedish women. Am J Clin Nutr. 2010;91(5):1268-1272
(4) Als-Nielson, B., W. Chen, C. Gluud, and L.L. Kjaergard. 2003. Association of funding and conclusions in randomized drug trails: A reflection of treatment effect or adverse events? Journal of the American Medical Association 290:921-928.
(5) Lesser, L.I., C.B. Ebbeling, M. Goozner, D. Wypij, and D.S. Ludwig. 2007. Relationship between funding source and conclusion among nutrition-related scientific articles. Public Library of Science Medicine 4:41-46.