Now, there is something controversial for me to say, of all people. But a couple of thing recently have made me think. First of all there was a book, a really interesting one that I wold actually recommend to life course researchers called "Biological Consequences of Socio-economic Inequalities" (BCSI)edited by Barbara Wolfe and colleagues: https://www.russellsage.org/publications/biological-consequences-socioeconomic-inequalities
We noticed that the editorial group was made up to psychologists and economists. When I read the various chapters of the edited collection I was surprised to find hardly anything about how health inequality is 'endogenous'. This idea is often put forward by economists and as far as I understand it, it means that health inequality is a result of individual characteristics that sort people destined for poor health into less advantaged social and economic circumstances. At one time, my (highly valued) economics colleagues seemed to think these characteristics were genetic. A position rather similar to that of Boris Johnson's Margaret Thatcher Memorial Lecture (or whatever it was). I do not think they meant congenital diseases (or at least not once we had finished discussing how rare such diseases are). Rather it seemed that there was an idea about individual preferences that arose from the genes (what a social epidemiologist would call 'indirect selection' rather than 'direct selection'). A preference for hard work and self denial, for example, would tend to result in both good health and high income.
In the last few years it has become increasingly unlikely that 'genetics' would be able to explain such highly complex characteristics as preferences with any precision. So I wondered if that was one reason for the remarkable consensus between the psychologists and the economists who edited and wrote the chapters for BCSI. Instead, the theory being put forward was based around early life experiences and their consequences for later health. The idea is that early adverse experiences 'get under the skin' by a number of biological pathways: by influencing inflammatory responses, immune responses and, most exciting of all to some people, by 'epigenetic' mechanisms.
The epigenetic mechanism, as I understand it (again) is the way in which the environment (by which people mean everything from the next door cells to the neighbourhood) 'tells' certain genes whether or not to turn on the proteins for which they can act as a template. A gene which doesn't do anything much in most children, for example, may, in abused children, become 'myelinated' and turn on a protein that has a harmful effect. Furthermore, it seems that once this change to the workings of the gene has happened, it not only persists throughout life but even may be passed on to the next generation. So for example, the fact that the children of smokers are known to be far more likely to smoke themselves. Child abuse seems to be similarly 'hereditary' (though I never heard anyone suggest that this was epigenetic).
I am sure people can see where this kind of thing is going. Instead of blaming the individual for their poverty and poor health, we can just blame their parents! There is indeed a lot of evidence in the tradition of 'family stress theory' research to show that, not surprisingly, people find it harder to be 'good parents' under conditions of poverty. The problem is, there are such powerful inter-relations between material adversity, psycho-social adversity and poor health right across life. A person whose childhood was marked by low parental wages and poor housing will have started off with higher exposure to factors that produce inflammation (frequent infections for example) . They may well have done worse in school due to difficulties in studying. So they have a high risk to find themselves in a hazardous occupation and poor housing in their own adult lives. Until these different exposures are isolated from each other and from the child's relationships to its parents we should not jump to conclusions.
Ironically, it would rightly be impossible to do trial-like studies of such processes because no one would randomise children into poverty. But a better idea might be to randomise disadvantaged adolescents into a carefully supported school experience, with free healthy meals and warm, quiet study areas supplied. Even that sounds rather unethical though, when you think about it. How could one justify not providing the intervention to the control group?