This is new to me. So, apparently, it was long known (or believed) to be that there were/are people who eat white arsenic to become immune to certain diseases or to get healthier! Stories of these people were told in several parts of the world including Europe and several novels, poems etc. are based on these people.
In this interesting article, you can read whether this phenomenon is real or not. The author mentions as many of these literature examples as possible and like a detective, he tries to find the truth. I think it is a really good read if you enjoy history of chemistry.