Can that be right? I'm dubious. So I checked to see what these "biomarkers of stress" are:
diastolic and systolic blood pressure, triglycerides, and cholesterol (cardiovascular risk), creatinine (kidney function), and albumin (liver function)The authors say these are commonly used markers of stress, but they look to me more like general indications of health. On the other hand rich people today report being healthier than poor people used to, so that isn't quite right, either.
I don't know what to make of this. But if it's really true that whatever is making poor and middle class people less healthy than rich people has gotten much worse since the 1970s, that could explain a lot.