Multivitamins and cancer: a mixed bag

A major new study published this week in the Journal of the American Medical Association (JAMA)  came to the surprising conclusion that

"daily multivitamin supplementation modestly but significantly reduced the risk of total cancer."

The report included some caveats, such as the fact that all 14,641 participants were healthy male physicians.

But the result is still surprising, because other recent studies, some of them even larger, have concluded that vitamin supplements do not provide any significant health benefits.  On the contrary, some studies found that supplements could actually be harmful.  As I wrote last year, a very large study of 38,772 older women, who were followed for 25 years, showed that the risk of death INCREASED with long-term use of multivitamins, vitamin B6, folic acid, iron, magnesium, zinc, and copper.  That's death, not just cancer.  The authors of that study, Jaakko Mursu and colleagues, concluded that there is

"little justification for the general and widespread use of dietary supplements."

The new study, PHS II (Physicians' Health Study II) looked at overall death rates as well as cancer, and found that men on a daily multivitamin had fewer deaths, but too few to be statistically significant.

So we have a large study in men showing that multivitamins seem to reduce overall cancer, and maybe even death, but an even larger study in women showing the opposite effect.

A second study from last year, in 35,533 men, looked at vitamin E and selenium supplements. That study, also published in JAMA, found that risk of cancer INCREASED for men taking vitamin E, selenium, or both.

The media reports aren't helping to clarify things.  The NY Times proclaimed "Multivitamin use linked to lowered cancer risk, and the Wall St. Journal reported that "Multivitamin cuts cancer risk, large study finds."  Bloomberg News went right for the business angle, announcing that "Pfizer multivitamin reduces cancer 8% in men, study finds."

Compared to Bloomberg news, Pfizer's own website was remarkably restrained, saying only

"Centrum Silver was part of the recently published landmark study evaluating the long-term benefits of multivitamins."  

No claims about reducing the risk of cancer - surprisingly, the independent media made far stronger statements than Pfizer.  Not true of supplement manufacturer GNC, which was flashing a pop-up headline that "Taking a daily multivitamin could cut cancer risk", linking to a news article at the Boston Herald.

So what do we make of this new study?  Are multivitamins good for you after all?

The new JAMA study appears to be very well done.  It's a double-blind, placebo-controlled study in which half of the physicians received a daily multivitamin, Centrum Silver, and half received a placebo.  The participants didn't know if the pill they were taking was a vitamin or a sugar pill.  The authors report some minor conflicts of interest, but none of them work for or received major funding from Pfizer (PFE, the manufacturer of Centrum).  So how to explain the seeming contradiction with two larger studies published only a year ago?

To answer this question, we must look at the details of the study itself.  This study looked at 21 different types of cancer risk.  For most cancers - colon cancer, prostate cancer, lung cancer, pancreatic cancer, lymphoma, leukemia, melanoma, and others - multivitamins did not provide a benefit.  But when all the numbers were added up, the effect was just large enough to be "significant", at a level of p=0.04.  More on that in a moment.

Here are the raw numbers: among the 7,317 men who took a daily multivitamin, there were 1,290 cases of cancer over the 11-year study.  Among the 7,324 men who took a placebo pill, there were 1,379 cases.  That's about 1.2% more - far less than the 8% reported by Bloomberg News. The statistical analysis showed that this difference had a p-value of 0.04, a result the authors considered significant. When the authors looked only at men with no history of cancer, the effect was smaller, and not statistically significant.

One explanation of the new finding is that the effects were indeed due to chance. Let's look at that p-value of 0.04. In much of the scientific literature, any p-value below 0.05 is considered "significant," but this has been widely criticized, in part because it encourages binary "true, false" thinking that is not the way scientists actually think. Also, the "0.05 threshold actually represents evidence much weaker than the number "0.05" suggests. A back-of-the-envelope Bayesian calculation shows that if the cancer-preventing power of multivitamins was a 50:50 proposition before this study, then after this study there is still a 10-26% chance that the cancer prevention claim is wrong. If we thought that prior evidence made this effect less than 50:50, (say 25:75), then the study has roughly a 25-50% chance of being wrong.* Either way, I won't be stocking up on Centrum Silver anytime soon.

Looking at this small effect, and at the contradictory results from other studies, neurologist Steven Novella writes in his blog that

"About the only thing we can say with a high degree of confidence is that there is no large risk or benefit from taking a multivitamin. There may be a small benefit, no benefit, or even a small harm."

That's a good summary.  So should men take a multivitamin?  Well, it's your money, but if you don't have a vitamin deficiency, it's probably not worth it.  Should women?  The evidence still says no.

*Thanks to Stanford biostatistician Steven Goodman (formerly of Johns Hopkins University) for crunching some numbers to produce Bayes factors.

What do the Presidential candidates think about science?

ScienceDebate.org recently posed 14 questions to President Obama and Republican presidential nominee Mitt Romney, and just a few days ago, the candidates answered all 14.  Can we learn what they actually think about science from these answers?  Well, maybe just a little bit.  

My first inclination, on going to the ScienceDebate2012 website, was to look for the candidates' positions on the two biggest scientific topics in the political arena today: evolution and global warming.  Somehow, ScienceDebate2012 only asked about one of these, which I'll get to in a minute.

The ScienceDebate2012 organization calls its list "the top American science questions: 2012", but the questions themselves are a disappointment.  They're what you'd expect from a committee: lots of nice-sounding, polite questions, but nothing that really challenges the candidates.  I guess SD2012 was afraid that the candidates might get all offended, or maybe that fewer scientists would sign their petition.  But if you read the answers, you'll see that the candidates just answered the question they wanted to hear, as politicians love to do.  Most of the answers describe policies we already know (for those who are paying attention to the campaigns), but an interesting surprise popped up: Mitt Romney has no fondness for NASA.  Jump to the bottom to learn more.

Most of the questions are big fat softballs, starting with the first one: "What policies will best ensure that America remains a world leader in innovation?" http://www.sciencedebate.org/debate12/   Good tough question, guys!  We only have 14 questions, and you waste one on this?  Unsurprisingly, the answers to this one just repeated campaign talking points.

Before looking at some real answers, let's start with the howlingly obvious question that ScienceDebate2012 failed to ask.  

The Un-asked Question: do you believe that evolution should be taught in public schools, and that it should be presented as the only explanation for how species arose?  

This question has only one right answer, as any biologist worthy of the name knows.  Evolution is the foundation of all of modern biology, genetics, infectious disease research, you name it.  And the U.S. is one of the few advanced countries where a significant number of its citizens don't accept evolution, opting instead for an archaic religious position that claims Earth is only a few thousand years old.  

We should know the candidates' answers.  In 2008, ten Republican presidential candidates were asked if they believe in the theory of evolution.  Only 7 said yes--but one was Governor Romney.  Back in 2007, he told the New York Times that "the science class is where to teach evolution," and that intelligent design was "for the religion class or philosophy class."  President Obama also supports evolution, and opposes teaching creationism in the science classroom. 

So the candidates agree on this one - at least they did in the past.  But Romney's fellow Republicans don't all agree. In particular, we need to ask Governor Romney: do you support the crazy religious extremism of your fellow Republican, Congressman Paul Broun from Georgia, who just announced that evolution, embryology, and the Big Bang theory are

 "lies straight from the pit of hell"?  

And Broun also stated that the Bible - and his wacko interpretation of it - should be used to run our government.  Any candidate for president should denounce this call for theocratic rule.

And by the way, if a Democratic Congressman said anything like this, I'd throw the same question at President Obama.

Now on to one of the real questions, on global warming. ScienceDebate2012 posed the question this way:

"The Earth’s climate is changing and there is concern about the potentially adverse effects of these changes on life on the planet. What is your position on cap-and-trade, carbon taxes, and other policies proposed to address global climate change—and what steps can we take to improve our ability to tackle challenges like climate change that cross national boundaries?"  

Obama's short answer acknowledges that "climate change is one of the biggest issues of this generation," and goes on to say he will "continue efforts to reduce our dependence on oil and lower our greenhouse gas emissions."  Vague generalities, and nothing he hasn't said before, but consistent at least.

Romney's answer, though, tries to have it both ways.  He first says that global warming is indeed happening and then says, basically, we need more research because it's controversial.  Here's how his lengthy answer begins: 

"My best assessment of the data is that the world is getting warmer, that human activity contributes to that warming, and that policymakers should therefore consider the risk of negative consequences."  

But then he pivots in the very next sentence and claims 

"there remains a lack of scientific consensus on the issue ... and I believe we must supported continued debate and investigation within the scientific community."  

So there you go: yes, global warming is a problem, but let's study it rather than do something.  At the end of his answer, Romney recovers a bit by saying he supports "robust government funding for research on efficient, low-emissions technologies."  So it appears he would support some action on global warming.  But his answer offers a troubling false claim about a lack of scientific consensus: the consensus is rock solid.

Now, I promised one surprise: a bit of new information.  Question 12 covers space exploration and is another softball: 

"What should America's space exploration and utilization goals be in the 21st century and what steps should the government take to help achieve them?" 

I expected some vague answers about how great America is (and both candidates did indeed deliver on that), but Romney surprised me with his answer.

Here's the surprise: Romney comes right out and says he will probably cut the NASA budget.  What he actually said in his answer was: 

"A strong and successful NASA does not require more funding, it needs clearer priorities."

In Washington-speak, this means "NASA has too much money and I will probably cut it."

So at least we know where Romney stands on space exploration.  He wants to downsize it and, apparently, outsource it to other countries.  Here's how he puts it later in his answer: 

"Part of leadership is also engaging and working with our allies and the international community. I will be clear about the nation’s space objectives and will invite friends and allies to cooperate with America in achieving mutually beneficial goals."  

If I worked for NASA, I'd be worried.