Multivitamins are affordable, convenient, and offer some reassurance when our diet falls short of ideal. However, a recent study involving nearly 400,000 people over 20 years found that they did not contribute to a longer lifespan and may even be associated with a 4% higher risk of mortality. Ian Sample consults JoAnn Manson, a professor of medicine at Harvard Medical School, to explore what the evidence reveals about the health benefits of multivitamins and how consumers can effectively navigate this complex market.