The only area I've played in there has been dating and it is super competitive. I never did white label stuff and almost all my traffic came from buying it and sending it directly to the dating sites. Starting from scratch in most any arena, I'd think potentially hundreds if not thousands of hours to start making much money.
While supplements and things like that are also competitive if that is your passion and you are knowledgeable about that topic I'd suggest starting there. There is money to be made and it will be a lot easier to create content about that (because you have an interest in it) than to come up with enough dating material to get people to sign up for dating websites.
Just about every market is saturated these days and the income is limited only by how much time, research, development and testing can be done. Be prepared to spend hundred of hours without making a dime of this is your first venture into the affiliate marketing arena.