This episode on the pellagra epidemic focuses on its prevalence in the U.S. in the early 20th century. Some of the scientific work done to understand it involves self-experimentation, and some of it is ethically problematic by today’s standards.
Research:

Behind the Scenes Minis: Paddles and The British Museum
31:02

Ashurbanipal
37:29

Six Impossible Episodes: Back-to-Court
41:15