An interesting debate on On Point tonight regarding taking vitamin and mineral supplements. They had two scientists (both legitimate experts on nutrition) but one was in favor and one was against taking them. Unfortunately, because of what we know about behavioral science, they are both right.
It is true that many of our diets are crap. And even if they are decent, there is good chance they are short of something important. Who knows what has phosphorous or manganese? So a multivitamin is a good insurance policy.
But here is where behavioral science comes in. As soon as you take your multivitamin, you feel overconfident that you have enough of everything. So for the rest of the day, you are going to put less attention on eating a good diet. So ironically taking a multivitamin increases the likelihood that you will need one. And because of the way our bodies digest food, it is better to get vitamins and minerals from food than from pills. So we are not doing ourselves any favors relying on our insurance policy.
It would be like someone with good car insurance driving faster and riskier because they are not worried about the crashes. Or someone with good health insurance refusing to quit smoking because the insurance will pay for any cancer treatment they might need. Why bother eating right when I can pop a multivitamin and go to BK?
So it is better NOT to take a multivitamin and concentrate on eating a good diet. If your diet sucks, it is better to take a multivitamin. But taking a multi-vitamin might make your diet suck rather than the other way around.