I’m often blown away by the fact that the posts I think are the least controversial are the ones I spend the most time discussing. Last week, I wrote about a large RCT that showed that supplementation with multivitamins in older males (physicians in this case) resulted in a reduced risk of getting cancer. Way more of you than I might have expected took exception to those findings. Your comments, however, were the kind we love here – chock full of evidence, data, and thoughtful questions. Therefore, I want to spend a few minutes addressing some of the larger points we can learn from this:
1) There’s a world of difference between supplementation with a multivitamin and mega-doses of vitamins. I’ve made this point in comments, but it’s worth repeating. Take food: just because eating too much is unhealthy doesn’t mean that you shouldn’t eat just enough. Or, take drugs: just because an overdose of a drug is harmful doesn’t mean that the correct dose isn’t a good idea. Dosing is important!
2) I’m totally against mega-doses of any one vitamin. There are some that are known to be harmful. Vitamin A, for instance, should be avoided in really large amounts. Your body often isn’t able to use more than it needs, meaning that all you’re doing – even if you’re not harming yourself – is creating really expensive, supplemented urine.
3) There’s a big difference between a cohort study and a RCT. If the study is retrospective, it is subject to huge recall biases. People who get cancer often report things more often as they search for a cause. Even prospective cohort studies can’t prove causality. So even if there’s an association, it doesn’t mean there is causation. A well-designed cohort study that shows an association merits a good RCT to see if there is causation. That’s what was done here!
4) Generalizability is always an issue. But you need to weigh your need for perfection against the greater good. Do you really believe other groups wouldn’t see a benefit? Do you really believe they’d see a harm. From a multivitamin?
5) Speaking of the greater good, I encourage you to always look at results holistically. MVIs are known to provide a nutritional benefit to people who aren’t getting the recommended supply of vitamins. They also now seem to prevent cancer, even if just a little. That’s the plus side. The down side? They cost something, but it’s very little in the scheme of things. That’s pretty much it. There are no real proven major side effects.
So when I look at that calculation, I think it’s probably worth it. For me. And, if asked, I’d make the same case to others. But I’m not saying that insurance should cover it – I’d need more analyses to determine that. I’m also not saying this should be mandated, or that people who don’t take them are crazy.
We should recognize, though, that studies like this are extremely expensive. They aren’t going to get repeated. There likely won’t be another decade-spanning study of multivitamin supplementation and cancer risk, perhaps ever. So this is as good as it gets. We can take research like this and accept the results, or we can ignore it. But often, we’re dismissing it because we don’t like the results more than because we know it to be flawed. That’s counter-productive, close-minded, and a waste of good money and time.