Supplements are the new obsession, even as doctors stay wary. I went inside one of the industry's biggest factories.

Kenzie Goer, senior vice president of planning and distribution at Thorne, showed us around the supplement company's newest warehouse in Summerville, South Carolina. Henry Taylor for BI As soon as I stepped inside the supplement factory, the sweet smell of red berries filled the air. It reminded me of being a kid and gorging on chewable multivitamins — a not-quite-natural "mixed berry" scent that was both nostalgic and vaguely medicinal. As factory tour smells go, it could have been much wor...