Another important factor I think is something that Robert Sapolsky's research has brought to light.[1]. Inequality and poverty itself causes significant health burden. That is to say, even when one accounts for the material disadvantages of the poor, different lifestyle patterns and so on, stratification itself contributes to adverse health outcomes in lower classes.

>"Psychologist Nancy Adler has demonstrated that how people rate how they are doing, relative to others, is at least as predictive of health or illness as are any objective measures such as actual income level, and research by epidemiologists Richard Wilkinson and Kate Pickett has shown that by just about every health indicator—infant mortality, overall life expectancy, obesity, you name it— inequality can be even worse than poverty. In the Whitehall studies, Marmot found a fourfold difference in rates of cardiac disease mortality between the lowest and highest rungs of the British Civil Service, despite the fact they were all paid a living wage"

All of the outcomes based effects on death in this article are of course real, but it's astonishing that, according to the research of Sapolsky and others, inequality itself can cause stress and inflammation responses that can account for up to half of perceived difference in health outcomes.

American society by and large is simply significantly more stressed and it has real impact on the biology of the population.

[1]https://newrepublic.com/article/153870/inequality-death-amer...