Despite all the research on vitamins and health, we have only a handful of rigorous scientific studies on the benefits "true" multivitamin: a pill that provides essential vitamins and minerals at the relatively low levels that the body normally requires.
The Physicians' Health Study II is the best study completed so far. It was the first and only large-scale randomized clinical trial to test a commonly taken multivitamin like the ones most people take, containing the daily requirements of 31 vitamins and minerals essential for good health.