Here is the short section from the book regarding inequality and health  
  
Even ignoring the question of access to health care, inequality by itself is detrimental
to good health.  In fact, emerging research indicates that inequality harms the health of
the rich as well as the poor, although certainly not to the same extent (Wilkinson 1997).
Even, the U.S. government's own Institute of Medicine reported: "... more egalitarian
societies (i.e., those with a less steep differential between the richest and the poorest)
have better average health" (Committee on Assuring the Health of the Public in the 21st
Century 2006, p. 59). Just how would inequality harm the health of rich people?  Unequal
societies are more stressful because the privileged must exert control to protect their
privileges from the poor.  This control creates stresses for the controllers as well as
the
controlled.  Recall how Adam Smith expressed the insecurity of the property owners who
felt themselves to be under siege.
  
More ominously, when inequality is combined with millions of people without access to
health care, the threats to health become multiplied many times over.  People weakened by
the stresses associated with poverty are less able to fight off diseases.  The compromised
immune systems of poor people without adequate health care provide an excellent
environment for diseases to mutate, inevitably becoming more resistant to medical
treatment or perhaps even lethal.  Oftentimes, diseases that arise in such conditions have
more social mobility than the people who carry them.  As a result, the pathogens bred in
poverty can strike the wealthy as well.  So, the growth of the uninsured population
presents a danger even for people with good health insurance.
  
To make matters worse, poverty tends to make people more susceptible to dangerous behavior
patterns, such as the sharing of needles among drug addicts.  Such activities leave them
even more prone to disease, which ultimately puts the rest of society at risk.
   
Michael Perelman