I wonder how much this effect is due to lifetyle (e.g. diet) and how much is due to preventative healthcare? Certainly poorer people in the U.S. would be less likely to see a doctor due to the substantial costs involved and thus not get early treatment for preventable diseases.
This suggests it's not due to healthcare effects: though healthcare for the rich is surprisingly bad in the US, I don't think it's so bad as to be on par with the poorest Western European groups. It suggests that the cause is something else, like living far from extended family or eating synthetic imitations of food.
