This comes up about once a year.
If you have scurvy, vitamin C will cure you. This incontrovertibly shows that vitamins have an effect on the body.
A multivitamin isn't a panacea. It's just insurance in case you're deficient in any given vitamin.
If you're a lazy slob eating junk food, a multivitamin isn't going to protect against that lifestyle. If they're going to do a worthwhile study, they need to include the overall beginning health of the individuals at the beginning of the study. They also need to cover the quality of life for them.