Thursday, November 1, 2012
Multiple concerns about multivitamins
My regular readers already know my deep skepticism about the benefit of vitamin supplements in well-nourished healthy people. My post last year summarized the available studies about many vitamins and ran under the headline "A Reminder to Dump Your Multivitamin." Thus far, large randomized studies about vitamins have tended to study a single vitamin at a time usually in fairly high doses. That makes a lot of sense. If you want to figure out if vitamin E prevents heart attacks, design a trial in which lots of people get either vitamin E or placebo. (It doesn't prevent heart attacks.)
Recently the Journal of the American Medical Association published the results of the first large randomized trial to study the effects of a multivitamin. The trial began in 1997 and enrolled 14,641 male U.S. physicians aged 50 years or older. It randomized the men to a daily multivitamin or a placebo.
The multivitamin used was the same formulation as the formulation of Centrum Silver at the time, which has 30 different vitamins and minerals. The men were followed for an average of 11 years. New diagnoses of cancer (except non-melanoma skin cancer) and deaths were counted for both groups.
It's important to note that this was part of a larger study to test the effects of a multivitamin on cancer, cardiovascular disease, eye disease and cognitive decline. The current results publish only the cancer findings. The effects on cardiovascular disease, eye disease, and cognitive decline will be published separately.
Especially to a skeptic like me, the results were interesting. The multivitamin group had slightly fewer new cancer diagnoses than the placebo group. The media is reporting the decrease as an 8% lower risk, which is true, but I don't think gives us a clear mental image of the magnitude of the benefit.
Imagine two groups each of 769 older men. If one group took the multivitamin for a year and the other group took the placebo for a year, the vitamin group would have 13 new cases of cancer and the placebo group would have 14. So for every 769 men taking a multivitamin for a year one new diagnosis of cancer is prevented.
Total mortality and mortality due to cancer were the same in both groups. The study was too small to detect differences in occurrence rates of specific types of cancers (i.e. lung cancer, colon cancer, etc.).
Two objections demand to be raised. First, why would you test 30 different vitamins and minerals together? It's conceivable that some of the ingredients have synergistic effects and work differently in combination than they do individually, but it seems that the scientific method suggests the opposite approach. First figure out the effects of each ingredient, then test some combination. The current results leave us completely mystified about which of the ingredients (or combination of ingredients) is responsible for the effect.
The authors state that the trial studied the effects of multivitamins because so many people take them, but I am left wondering whether the trial was designed to raise our understanding or increase Centrum Silver sales. (Pfizer, which sells Centrum Silver, supplied the placebo and the multivitamin for the trial, though it did not design or conduct the study. The study was funded by the NIH.)
The other objection is that the difference between the cancer incidences in the two groups barely rose to the level of statistical significance. Bear with me while I delve into the statistics briefly. Statisticians use a measure called a P value to decide whether a measured difference between two groups might have been due to chance alone and not due to the intervention being studied.
The P value answers this question: If the intervention being studied is actually irrelevant (in this instance, if the multivitamin and the placebo have equivalent health effects) how likely is it that the two groups would show such different numbers (in cancer incidence, in this case) by chance alone? By convention, any P value less than 0.05 is considered statistically significant.
That is an arbitrary choice agreed on by statisticians, but there is no math or science behind that number. We just need some cut-off point, so we decided that 0.05 is statistically significant and 0.06 is not. That still means that for all the randomized trials we do, if the null hypothesis is true (meaning, if the medicine is just like the placebo) 1 time in 20 we'll get a result that shows that the two are different in a statistically significant way, meaning we'll get a false result by chance. The P value in this trial for the difference in cancer incidence for the two groups was 0.04. Yes, that's statistically significant, but just barely.
So what can we conclude?
First of all, this teaches us nothing about multivitamins in women or in men under 50.
Second, the design of the trial is very solid. It was randomized and blinded. So we should take the result at face value, that for men over 50 taking a multivitamin daily makes a small decrease in the risk of cancer (but not in dying of cancer). This effect is much smaller than quitting smoking. So it makes a lot of sense to quit smoking before you try to figure out whether or not to take a multivitamin.
My suggestion for now is to wait for the rest of the results from the trial. For example, if the cardiovascular results are even slightly negative, suggesting that the multivitamin increases stroke or heart attack risk by a small amount, that may overwhelm the cancer benefit.
For the time being I'm still not recommending a multivitamin for healthy adults, or taking one myself.
Learn more:
Multivitamin Cuts Cancer Risk, Large Study Finds (Wall Street Journal)
Daily multivitamin appears to slightly lower cancer risk in older men (Los Angeles Times Booster Shots)
Multivitamin Use Linked to Lowered Cancer Risk (New York Times)
Multivitamins in the Prevention of Cancer in Men, The Physicians' Health Study II Randomized Controlled Trial (Journal of the American Medical Association)
A Reminder to Dump Your Multivitamin (my post from last year reviewing the current studies about vitamin supplements, with links to my prior posts about vitamins)
Albert Fuchs, MD, FACP, graduated from the University of California, Los Angeles School of Medicine, where he also did his internal medicine training. Certified by the American Board of Internal Medicine, Dr. Fuchs spent three years as a full-time faculty member at UCLA School of Medicine before opening his private practice in Beverly Hills in 2000. Holding privileges at Cedars-Sinai Medical Center, he is also an assistant clinical professor at UCLA's Department of Medicine. This post originally appeared at his blog.
Labels: Albert Fuchs, guest post, prevention, vitamins
posted by Albert Fuchs, MD at
9:00 AM
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Members of the American College of Physicians contribute posts from their own sites to ACP Internistand ACP Hospitalist. Contributors include:
Albert Fuchs,
MD
Albert Fuchs, MD, FACP, graduated from the
University of California, Los Angeles School of Medicine, where he
also did his internal medicine training. Certified by the American
Board of Internal Medicine, Dr. Fuchs spent three years as a
full-time faculty member at UCLA School of Medicine before opening
his private practice in Beverly Hills in 2000.
And Thus, It Begins
Amanda Xi, ACP Medical
Student Member, is a first-year medical student at the OUWB School
of Medicine, charter class of 2015, in Rochester, Mich., from which
she which chronicles her journey through medical training from day
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Zackary Berger, MD, ACP Member, is a primary care doctor and
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db's Medical Rants
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DrDialogue
Juliet K. Mavromatis, MD, FACP, provides a conversation about
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Matthew Mintz, MD, FACP, has practiced internal medicine for more
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Vineet Arora, MD, FACP, is Associate Program Director for the
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Ryan Madanick, MD, ACP Member, is a gastroenterologist at the
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Peter A. Lipson, MD, ACP Member, is a practicing internist and
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Also known as the Green Journal, the American Journal of Medicine
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The Public Library of Science's open access materials include a
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One of the most popular anonymous blogs written by an emergency
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