Social class, poverty and health inequality

What does an insecure position actually do inside the body? Psychosocial explanations name a chain that runs from social experience to physiology. The starting conditions are low control over one’s own work and life, unpredictability, and a low place in a hierarchy that other people can see. The American epidemiologist Leonard Syme summarised the recurring finding as control and predictability rather than income alone. Robert Karasek’s demand-control model of job strain predicts ill health best when psychological demands are high and decision latitude is low — the combination found on assembly lines, in casual building work and on some nursing shifts, rather than in demanding but self-directed jobs. When the brain appraises a situation as threatening and uncontrollable, it activates two linked systems: the sympathetic-adrenal-medullary axis, which releases adrenaline and noradrenaline, and the hypothalamic-pituitary-adrenal axis, which raises cortisol. Both are useful for a short emergency, and both are harmful when they stay switched on for months because the threat never resolves. Bruce McEwen and Eliot Stellar called the resulting cumulative wear allostatic load: the same hormones that protect in the short term gradually produce raised blood pressure, abdominal fat deposition, insulin resistance, impaired immune function and damage to the hippocampus. Arline Geronimus named the faster biological ageing of people exposed to repeated social adversity weathering, and the tally can be measured through blood pressure, waist circumference, cholesterol, cortisol and inflammatory markers. This is why the stress pathway is more than a metaphor, and why the Whitehall studies found that conventional risk factors such as smoking and cholesterol explained only part of the mortality gradient: the remainder appeared to travel through position and control. The consequence for nursing is that reassurance is not a treatment. What lowers allostatic load is a real change in predictability, control or security — a fixed appointment, a written plan, a waiver of the fee — not advice to worry less.

If social position affects health, health must also affect social position, and a careful nurse should not assume the direction. Three positions are distinguished in the literature. Social causation holds that class position produces illness through the material, behavioural and psychosocial pathways. Health selection, also called reverse causation or drift, holds that people who are already ill move downward into lower classes and lower incomes: a man who becomes breathless may lose the heavy work that paid him, then his income, then his place in the hierarchy. The two are not rivals for the whole gradient; both operate, and the difficult question is how much of the association each explains. The 1980 Black Report in Britain set out four candidate explanations — measurement artefact, natural or social selection, materialist or structural causes, and cultural or behavioural causes — and concluded that materialist explanations carried most weight. Stronger evidence came later. Because the gradient persisted and even widened across the very period in which the main causes of death shifted from infections to heart disease and cancer, a single downward-drifting group cannot account for it. Natural experiments added weight: the Dutch Hunger Winter of 1944–45 produced lifelong metabolic effects in people exposed before birth, and the sharp rise in mortality in Russia during the 1990s followed social and economic dislocation rather than any epidemic. Health selection nevertheless does occur, and it matters most for conditions that strike in childhood, interrupt schooling and change the trajectory that follows. The practical test is temporal: ask which came first, the illness or the downward move, and look for a change in circumstances that preceded the illness rather than followed it.

Because the gradient is a claim about distributions, it is measured with tools that a nurse should be able to read. A poverty line converts a standard into a number. The World Bank’s international poverty line, revised in 2022 to 2.15 US dollars per person per day in 2017 purchasing-power-parity terms (adjusted for what money buys in each country), is an absolute threshold used for global comparison. Relative thresholds are national: the European Union counts a household as at risk of poverty when its equivalised disposable income — income adjusted for household size — falls below 60 per cent of the national median, and the OECD often uses 50 per cent. The Gini coefficient summarises how unequal the whole distribution is, running from 0 when everyone is equal to 1 when a single household takes everything. To compare health between classes rather than merely describe it, analysts use the concentration index, which measures how closely ill health is tied to income rank, and the slope index of inequality, which expresses the absolute difference in a health outcome between the most and the least advantaged ends of the social scale. Health financing has its own threshold: the World Health Organization and the World Bank call out-of-pocket payments catastrophic when they exceed 10 per cent of a household’s total consumption or income, and impoverishing when they push the household below the poverty line. Both are common where insurance is thin and fees are charged at the point of care, as in Cameroon after the cost-recovery reforms that followed the 1987 Bamako Initiative, when user fees were introduced to fund under-resourced facilities. The policy answer drawn by the 2008 WHO Commission on Social Determinants of Health, and later by the Marmot Review of 2010, is progressive universalism: act on the whole gradient, with effort proportional to need, instead of targeting only the poorest. Removing a fee at the point of use is one of the few interventions that changes poverty and health at the same moment.