My first comment is that I think this is why we have placebo-controlled double-blind studies.

My second is that I took a multi-vitamin for many years and I recommend caution in their use. For much of that time, when I went to the doctor for my yearly physical I would have elevated AST and ALT liver enzymes which is a marker of liver damage. All tests for typical causes of this (hepatitis, others) came up negative.

Finally my doctor asked if I took a multivitamin. I said yes and she told me to stop taking it. That was about 15 years ago and I have never had elevated liver enzymes since then.