The Journal of Economic Literature is the most prestigious journal for summarizing the findings of a field of research. Princeton Economist Agnus Deaton surveyed the literature on inequality and health. Deaton is not just anyone, there is talk about eventually awarding him the Noble prize.
Deaton starts his conclusions by writing:
"The stories about income inequality affecting health are stronger than the evidence"
He further concludes:
But who are you going to trust, one of the world's leading Health Economists in the Journal of Economic Literature, or Wilkinson and Pickets own(!) meta-study, and their claims on their book selling tour?
The Spirit Level makes a big deal about the association between inequality and health within American States. But in another paper Deaton and Lubotsky have shown that:
(from abstract) "Conditional on the fraction black, neither city nor state mortality rates are correlated with income inequality"
Here is the share of minorities in 2000 and Gini in 1999.
I did the regression to make sure: Controlling for the share of African Americans Gini has no statistically significant effect on life expectancy within American States (p value 0.431).
The Spirit Level authors are not only wrong, they are dishonest. They must be aware that their correlation within states has been proven to be due to demographic factors. They must be aware that the more heavy-weight surveys of the literature conclude that there is no robust relationship between inequality and life expectancy.
But they know that they audience does not know this, and exploit the trust of the readers to sell them a false view of the state of the science.