Abstract - Population health tends to be better in societies where income is more equally distributed.
Recent evidence suggests that many other social problems, including mental illness, violence, imprisonment, lack of trust, teenage births, obesity, drug abuse, and poor educational performance of schoolchildren, are also more common in more unequal societies. Differences in the prevalence of ill health and social problems between more and less equal societies seem to be large and to extend to the vast majority of the population.
After discussing the evidence and considering the overwhelming statistical correlation between income inequality and social ills, Wilkinson concludes that these relationships are likely to reflect a sensitivity of health and social problems to the scale of social stratification and status competition, underpinned by societal differences in material inequality.
http://www.fhs.sfu.ca/news/events/special-guest-speaker-dr.-richard-g.-wilkinson