Vitamins and dietary supplements are a $37 billion business. Joshua Johnson takes them … maybe you do, too. How do you know what’s actually in that bottle? Does it even work? We hear from a skeptic, a lobbyist and a cancer researcher. | Want to support 1A? Subscribe to our podcast and give to your local public radio station at donate.npr.org/1A. Email the show at 1a@wamu.org.