 While many people take multivitamins hoping to prevent chronic diseases and live longer, researchers didn't find evidence to back up any of those beliefs. They followed almost 400,000 American adults for more than 20 years. Now that's a thorough study. Participants came from diverse backgrounds and regions across the country. By comparing multivitamin users to non-users over this extended period, the researchers aimed to uncover any long-term benefits. What they found was surprising.