In "The Vitamin Myth: Why We Think We Need to Take Supplements," Dr. Paul Offitt tries to shed light on the origins of why we take vitamins, and highlights some recent studies showing vitamins are correlated with an increased risk of cancer and other health problems. He wrote a similar, shorter piece in The New York Times as well. The message is clear: vitamins are harmful, not helpful.
The basic premise is that your body absorbs synthetic vitamins differently than it does natural vitamins. Thanks to Linus Pauling, many people believe the myth that Vitamin C can cure the common cold and prevent other diseases (like cancer), and therefore the vitamin industry thrives on peoples' ignorance-- to our own detriment.
Offitt has impressive credentials, but I've looked at a few critiques of his pieces and wanted to post them here as well. The Linus Pauling Institute (no vested interest there!) argues that Offitt is cherry-picking the studies he quotes and misrepresents Pauling's positions. Since 40% of Americans are vitamin-deficient in their diets, it's better they get supplements than not enough vitamins, they say.
Paul Jaminet, a Harvard astrophysicist-turned-dietician and relational economist(!) writes a more scathing critique of the Offitt piece. He attacks the statistical techniques used in one of the studies Offitt cites. I'm sympathetic to this critique as I have "fit a curve" or two in my day as well. (Jaminet has some "halo effect" for me though because of his background and devotion to Ronald Coase.)
I tend to agree with this James Hamblin piece, on The Atlantic's website in June, that "(Vitamins) could shorten or extend your life; at this point, taking vitamins randomly is metabolic roulette." This is similar to Jaminet's conclusion that "nutrient needs differ among persons depending on their health and age, and whether a person will benefit from a nutrient depends on whether the rest of the diet is deficient in that nutrient. So any given supplement is going to be harmful in some circumstances, beneficial in others" (emphasis mine).
As Offitt and others point out, vitamins are not recommended for "otherwise healthy people." I make sure I eat a "ranbow on my plate" and keep track of my estimated nutrient intakes by entering everything I eat into myfitnesspal.com. I'm confident I'm getting the vitamins and balanced diet I need-- mostly through natural sources like the plants I'm consuming. So, I've given up my multivitamin. I know of other very health-conscious eaters and vegans who seem to supplement with vitamins "just in case." The studies cited in the articles above seem to show the "just in case" might mean too much, and harmful.
If you're taking a multivitamin, why are you taking it?