Hugh Pickens writes:
Scott Adams of Dilbert fame writes on his blog that science's biggest fail of all time is 'everything about diet and fitness':
I used to think fatty food made you fat. Now it seems the opposite is true. Eating lots of peanuts, avocados, and cheese, for example, probably decreases your appetite and keeps you thin. I used to think vitamins had been thoroughly studied for their health trade-offs. They haven’t. The reason you take one multivitamin pill a day is marketing, not science. I used to think the U.S. food pyramid was good science. In the past it was not, and I assume it is not now. I used to think drinking one glass of alcohol a day is good for health, but now I think that idea is probably just a correlation found in studies.
According to Adams, the direct problem of science is that it has been collectively steering an entire generation toward obesity, diabetes, and coronary problems. But the indirect problem might be worse: It is hard to trust science because it has a credibility issue that it earned. "I think science has earned its lack of credibility with the public. If you kick me in the balls for 20-years, how do you expect me to close my eyes and trust you?"
It's not a question of it being a BAD thing. It's a question of whether it in fact is a GOOD thing.
Multiple long-term studies [annals.org] have found essentially zero long-term health or survivability benefits from daily multivitamin usage compared to people who don't take them.
While the theory around multivitamins is good, and your point of "how could they NOT be doing something?" is an intuitive one, the numbers don't bear out them having any significant health benefits over taking a daily placebo.
"It's not a question of it being a BAD thing...."
Or maybe it is...
Vitamins and Supplements Linked to Higher Risk of Deathhttp://healthland.time.com/2011/10/11/vitamins-and-supplements-linked-to-higher-risk-of-death-in-older-women/ [time.com]