Thanks for the paper (that's a lot of authors!). The complexity you mention makes it difficult to determine whether substance X (caffeine, alcohol, eggs, etc.) has a net positive or negative for any given person when it comes to health benefits. Coffee has been linked to some positive health effects, but maybe only for those people who don't get the jitters....that's the sort of thing that would be cool to know. Until then, I'm just going to listen to my body and minimize consumption.