Kawachi and others argue that inequality breaks down social values, such as trust and support, that protect against both physical and mental illness. In a recent op-ed in The New York Times, epidemiologists Richard Wilkinson and Kate Pickett of the University of York in the United Kingdom took the argument even further. They claim that the reason more unequal countries like the United States see higher rates of schizophrenia and other mental illnesses is because inequality causes “social corrosion” that damages the individual psyche.
Others aren't convinced. John Lynch, an epidemiologist at the University of Adelaide in Australia, says that although he started out as a “true believer” in the income inequality hypothesis, a string of negative and equivocal studies turned him into a skeptic.
Back in a 2004 paper, for example, Lynch and colleagues reviewed 98 cross-national studies and found “little evidence” of a consistent link between income inequality and health, although the United States displayed a more robust association than others. Working on well established public health goals such as reducing smoking and improving the living conditions of the poor will likely have more direct health impacts than targeting relative income gaps, he says.
Even if the correlations Kawachi and others have found hold up, there's no strong evidence that income inequality, per se, is directly damaging people's health, says Angus Deaton, an economist at Princeton University. In American cities and states where there are large proportions of African-Americans, for example, racism, poor health care, and political disenfranchisement could just as easily explain poor health outcomes as income inequality, he says.
Deaton argues that extreme inequality is a risk to health chiefly because it skews politics to favor the rich and powerful in society. “I get angry” over Wilkinson's claim that psychological stress is the primary culprit, because it completely deflects from the real issues,” he says.