I will admit that this is somewhat compensated by lower-level workers having to worry more about making ends meet, but I don’t think this comes close to making up for work-related stress - at least not in first-world countries where low-level workers are relatively well-off.

As for the possibility of decreased CHD resulting from a switch to fish from meat, I really wonder whether those in the occupied countries had much access to fish. However, I haven’t seen any data on this. I haven’t heard that those in unoccupied countries like Britain had lower CHD rates.

“The social gradient” is an observation, not a theory — it can’t be “put to rest” unless the data turns out to be false. As for its explanation, sure, IQ could be important, especially in controlling what job you end up getting. Whether IQ remains important after degree of control over one’s job has been accounted for remains to be seen.

A study that equates IQ across the groups being compared is the famous study of London transit workers in the 1950s that found that drivers of double-decker buses had a higher rate of heart attacks than the ticket takers on those buses. The first explanation was that the ticket takers got more exercise (presumably up & down the stairs); I have suggested they got more sunlight and stood much more so they slept better; others have suggested that driving in London traffic is stressful. No one has proposed that the crucial difference is IQ.

Robert Levenson’ and other emotion researchers find that if you have subjects watch a disturbing video of an arm amputation and are told to keep a poker face and show zero emotion in response to it, they have 2x the cardiovascular stress in heart rate and blood pressure as subjects who watch it and respond naturally. And generally, suppressing any emotion, positive or negative, causes much added cardio stress.

Perhaps immigrants, especially from radically different cultures, must suppress a lot of emotion, or feel cognitively overwhelmed, and that causes heart disease. The depression research is showing great increases in heart disease among depressives, based on correlational studies — again more guessing, but interesting. Stress hormones like cortisol are tied to depression and heart disease.

When you don’t know what you don’t know, you have to be very careful about making causal claims — it should be written on wind and running water!

As for the “social gradient” theory of CHD, I think that has been definitively put to rest be Deary and Gottfredson: Childhood IQ is moderately strongly correlated with adult socioeconomic position. Lower IQ is also associated with increased rates of all-cause mortality (1, 2), cardiovascular
disease (2–4), hypertension (5), contact with psychiatric services (6), and other negative health outcomes (7). These associations
remain after controlling for socioeconomic position in early life. http://www.udel.edu/educ/gottfredson/reprints/2005scienceletter.pdf See also Gottfredson’s “Intelligence: Is it the epidemiologists’ elusive ‘fundamental cause’ of social class inequalities in health?” http://www.udel.edu/educ/gottfredson/reprints/2004fundamentalcause.pdf

Further, as to “stress”, heart disease rates in German-occupied Europe during WW2, in The Netherlands and Norway for example, went down, exactly the opposite of what one would expect if stress were a cause.