New results published online today from the Physicians’ Health Study II (PHS II), showed that participants who took a daily multivitamin for 11 years had 8 percent fewer cancers compared to participants who took a daily placebo. The study is a large randomized controlled trial involving over 14,600 male physicians aged 50 and over.
The study is published in the Journal of the American Medical Association.
Though the reduction in incidence is relatively small, it is significant, and the PHS II is a large, rigorous and well-respected double-blinded randomized trial. (In the study, one group took a multivitamin and one group took a placebo; neither the subjects nor the doctors knew which was which.)
Yet at first blush, this new result seems to run counter to AICR’s recommendation not to rely on dietary supplements for cancer prevention. So what to make of it?
A Closer Look
Let’s dig a little deeper, into some of the other findings from the PHS II reported today. The observed reduction in incidence is for all cancers considered together — multivitamin use did not offer protection against site-specific cancers like those of the prostate, colorectum, lung and bladder. Neither did multivitamin lower risk for cancer death.
Also, subjects were men in middle-age and older, so even if future studies confirm these results, it still won’t be possible to generalize whether multivitamin use might offer similar protection in women, or in young men.
A Single Study
Studying cancer prevention in humans is a notoriously complicated affair, particularly with a clinical trial, because cancer can take so long to develop, and those aspects of a person’s lifestyle that influence cancer risk (diet, level of activity, etc.) continually shift from day to day. This is why any single study, however rigorous, must be considered alongside all of the research that has come before it. Scientific consensus can and does change when necessary, but only when necessary — and only with deliberate care.
And considering all of the evidence is exactly the task that AICR and WCRF have set for ourselves, with our Continuous Update Project (CUP). The CUP is a massive database of research linking lifestyle and cancer risk; new results are constantly being added and periodically reviewed.
This new study will be added to the numerous studies already in the CUP and will get assessed as part of the total body of evidence by our experts. Until that time, however, AICR continues to caution individuals to look to the whole diet, and not dietary supplements, for cancer protection. (Despite today’s finding, the research on supplements and cancer risk is conflicting, with some studies showing that high doses of certain supplements raise risk.)
The Whole (Food) Story
Whether or not these results are confirmed, we already know that we could prevent more than 8 percent of cancers — approximately 1/3, in fact — if we adopted healthier habits, including moving more and eating for a healthier weight. And we continue to recommend looking to a healthy, varied diet high in plant foods to lower your cancer risk. You can read all of our recommendations here.
Note that there’s a bit of nuance in AICR’s recommendation on dietary supplements. Whether you take a multivitamin or not is up to you and your doctor or registered dietitian. You may, for example, belong to one of the many groups who for a variety of reasons stands to benefit from a daily vitamin so as to avoid a nutritional deficiency. (For more information, see the National Institutes of Health Office of Dietary Supplements).
What AICR cautions against is relying on supplements to provide cancer protection. A multivitamin is no substitute for a balanced diet, because evidence shows that it’s whole foods, not individual or isolated food components, that lower risk. A diet rich in plant foods provides the vitamins and minerals found in multivitamins alongside fiber and water (which help you manage your weight, a major cancer risk factor) and phytochemicals that show anti-cancer potential.
Today’s results from the PHS II contribute to the discussion, and will become a part of the AICR/WCRF Continuous Update Project, and as such will help to shape AICR’s evidence-based advice in years to come.