Photo: Muneer Ahmed ok / Unsplash
The idea of a “social scale” may be metaphorical, but a real and perceived societal ranking have real consequences for the health of an individual. The influence of social structure on health and disease is extensively studied in high-income countries, where coronary artery disease (CHD) is the main primary cause of death.
In these societies, the relationship between an individual’s social position and their risk of coronary heart disease is surprisingly consistent, with disadvantaged populations being more susceptible suffer from and die from the disease. Despite the clarity of this evidence, public health personnel have not yet reached a unified consensus on why these inequalities occur and what can be done to reduce them.
Lifestyle factors such as diet, physical inactivity or smoking, and their effects such as hypertension, only partially explain the excessive burden of coronary heart disease in disadvantaged groups. Yet primary prevention efforts seem to focus on these health behaviors rather than on other factors related to social inequalities. In fact, targeting only lifestyle is likely to exacerbate inequalities in post-industrial societies.
Investigating inequalities in populations who have not adopted Western diets and activity levels – a difficult undertaking given the proliferation of this way of life around the world – could be a way to face the underlying hypothesis that differences in behavior are responsible for the inequality observed in coronary heart disease. Now in eLife, Adrian Jaeggi (University of Zurich and Emory University), Aaron Blackwell (Washington State University) and colleagues based in the United States, France and Germany report the most comprehensive report study on social structure and health in a pre-industrial society in the Bolivian Amazon known as Tsimane.
This population depends on subsistence agriculture supplemented by hunter-gatherer practices, which translates into an extremely physically active life and a diet rich in fiber and micronutrients. In turn, they have remarkably modest rates of obesity and hypertension, and the lowest prevalence of biomarkers of poor arterial health ever recorded in the world. Thus, any putative relationship between social position and heart health is unlikely to be the result of differences in health behavior.
Overall, Jaeggi et al. discovered coherent links between wealth-related circumstances and blood pressure among the Tsimane: the poorer the individual, the higher their blood pressure. In people over 15 years of age, the pressure on the artery walls during and between heartbeats was lower in people with higher household wealth, that is, those with household goods. most common: this may include traditional products made from local organics, industrially produced items acquired through trade or purchase, and livestock. The researchers also studied the association between wealth inequality and overall health in several geographically separated communities – defined as clusters of households connected via kinship networks that produce or consume food together. They found that communities with greater inequality between rich and poor members had higher blood pressure.
Most Tsimane have normal blood pressure. This means that the associations between wealth and individual blood pressure within communities, or between inequality of wealth and overall blood pressure between communities both capture variations below a clinically significant level. However, these results are not unimportant: in post-industrial societies, small reductions in blood pressure in the general population Has proved effective in reducing the incidence of coronary heart disease.
If no member of the Tsimane population leads an unhealthy life and if they all have little or no access to health care, then what causes higher blood pressure in poorer adults and in more unequal communities? Psychosocial mechanisms and pathways leading to poor health may provide a response, drawing on how the feelings that result from inequality, dominance or subordination can modify directly biological processes. Social hierarchies, maintained by societal power arrangements, lead disadvantaged populations to be disproportionately exposed to psychosocial stressors such as lack of community support, weak control and autonomy, and an imbalance in effort and reward. In turn, psychosocial stress can have a severe impact on the body, triggering a sustained fight-or-flight response and altering the hormonal system that controls biological responses to stress.
Jaeggi et al. therefore tested how psychosocial factors related to wealth and the unequal distribution of wealth may have influenced Tsimane feelings and interactions (e.g. depression, social conflict) or altered their body chemistry (e.g. level cortisol, the stress hormone in urine). Analyzes found a weak link between these factors and increased blood pressure levels in individuals who have less wealth or come from more unequal communities.
However, this link may only be weakly supported by analyzes because the markers used may have insufficiently measured psychosocial stress. It may therefore be of interest to also examine whether a pathway can be identified by examining C-reactive protein, an inflammatory biomarker of blood pressure which is relatively high in the Tsimane population. Yet, detecting these small effects in such a healthy society requires a large sample size, and psychosocial markers were only collected from a subset of participants with blood pressure data: it is therefore more probable that the analyzes were underfed.
The Tsimane are increasingly exposed to psychosocial stress as contact with majority ethnic groups increases and their economy becomes more integrated. These developments prompt researchers to explore the individual and macro-level mechanisms of health inequalities in Tsimane, and remind us, once again, to look beyond lifestyle to tackle public health issues.
Milagros Ruiz is with the Department of Epidemiology and Public Health Research at University College London.
This article was originally published by ELife Magazine and has been republished here under a Creative Commons Attribution license.