Wednesday, October 24, 2007

Social Inequality and Health

This was the hook:
Intriguing parallels between civil servant and nonhuman primate hierarchies suggest that highly stratified societies foster health inequalities. Determining how social differences translate into chronic disease remains a challenge, but neuroendocrine pathways appear to play a role.
to a short paper in PLoS Biology that was part of a "Collection on Poverty"
First of all, what happened to Romania, Slovakia and Croatia in their logo below? Is this a prediction of global warming's effect on the Black Sea and the Mediterranean?This paper focused on: how do we explain health inequalities with respect to the stress and changes in endocrine pathways caused by being at the bottom of the social ladder? I'm happy that they referenced Sapolsky and the parallels with other primate hierarchies and measures of cortisol, but I feel that they could have referenced more of the literature on the effect of skin color and racial discrimination on job attainment and health problems, for example. Most of what they talk about in this paper is the inverse gradient between disease related traits and social level. When risk factors are controlled for, (or attempted to control for), they still find that 2/3 of the gradient remains unexplained. Interestingly they find that cancer mortality does not follow that same inverse gradient. Also, interestingly, the risk associated with stress from low status was greater in females.
Since, after controlling for behavioral factors and general obesity they still find much of the gradient unexplained, they transition into their discussion:
That behavior-related factors did not provide a full explanation for the social gradient in metabolic syndrome is consistent with the operation of direct psychosocial and neuroendocrine pathways linking lower social status to CHD risk
...In contrast to this social “embodiment” perspective, it has been argued that biological integrity, in the form of inherited advantage, is the real cause of social inequalities in health.Cognitive function is a high-level expression of this property, and analysis of the changes in test scores over the first ten years of life in a population-based study (the 1970 Birth Cohort) emphasizes the importance of environmental influences. Cognitive performance was first measured at 22 months of age. Children who ranked low at baseline rose through the ranks if their parents were affluent, and conversely, children who ranked high at baseline fell back if their parents were poor. By age seven, the two groups had crossed over in the rankings, whereas children who had both high initial test scores and high social class parents remained near the top of the ranking, and vice versa [8]. These and numerous other findings suggest for the majority of those born without congenital disease, and regardless of the endowment of health capital, a poor early socioeconomic environment is likely to undermine development and later health prospects.
then the author goes on to discuss the lessons to be learned from work by R. Sapolsky on baboons:
This correlation matches the proposition of the late Per Bjorntorp that activity of the hypothalamic-pituitary-adrenal axis links psychosocial factors to metabolic syndrome [11]. Further, Sapolsky provided an example of the physiological effects of hierarchy, free of confounding by smoking and alcohol consumption, both of which influence HDL cholesterol levels.
So can we measure "stress"?
Many questions remain. The quest for a universal stress biomarker, the Holy Grail of “stress biology,” may be a vain enterprise, but with respect to obesity, diabetes, and cardiovascular disease, metabolic syndrome proves to be a useful construct.
I guess they think that metabolic syndrome is a good measure since they find that it is affected only a little by behavioral factors and general obesity.
Finally, props to the author for including info on this study on the effects of football (the real football) results on mortality rates - when you experience stress via your national team's loss in a major tournament:

Box 1. The Power of Mind-Body Interaction: Knockout Stress Triggers Cardiovascular Death among Soccer FansMortality among adults 45 years or over in Holland on 22 June 1996—the day the Dutch football team was eliminated from the European championship—was compared with the 5 days before and after the match and in the same period in 1995 and 1997. Coronary and stroke mortality was increased in men on the day of the match (relative risk 1.51, 95% confidence interval 1.08–2.09). No clear rise in mortality was observed for women (1.11, confidence interval 0.80–1.56). Among men, approximately 14 excess cardiovascular deaths occurred on the day of the match [19].

The paper ends with this juicy outlook into future research possibilities:
More feasibly with the newly available high-throughput genotyping technology, we plan to harness Mendel's second law—nature's randomization—to compare stress hyper-responders with their more even-tempered counterparts. By comparing the lifelong effects of genotype with observed phenotype, we have the potential to break the confounding intrinsic to conventional epidemiology, to clarify what is cause and what is effect.

1 comment:

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