Freakonomic made it clear there can be subtle and unexpected correlations.
Here are two I will suggest:
1. Much of the difference between men and women in longevity has to do with the fact that men retain more serum iron. When we eat red meat, it accumulates. Too much iron causes a variety of health problems that women–who menstruate much of their lives–do not have.
I have seen few talk about this.
2. Part, at least, of the difference in overall health outcomes between white people and African Americans particularly, has to do with the greater difficulty the latter have in creating Vitamin D from sun exposure. Vitamin D is good for nearly everything, but folks with darker skin have a harder time creating it.
This is what I read, in any event.
It’s an odd and unexpected thing, and I don’t doubt for a moment that socioeconomic status and education play roles as well. But it’s still something I haven’t seen said.