Stress, poverty and disease are tightly linked according to Robert Sapolsky. His article in the December 2005 issue of Scientific American substantiates that there is a 10 fold increase risk for some diseases that can be attributed to the stress of being poor. That stress, apparently is exacerbated by the perception of poverty that is heightened in societies with wide income gaps, such as the U.S.. Studies cited (Michael G. Marmot of the University College London) in the text of the article debunk the idea that its simply lack of access to care and unhealthy lifestyles that are at the root of the disparities in health.

Interesting reading material suggested by the article include the following:
Mind the Gap: Hierarchies, Health and Human Evolution by Richard Wilkinson, Wiedenfeld and Nicolson 2000.
The Health of Nations: Why Inequality is Harmful to Your Health. Ichiro Kawachi and Bruce P. Kennedy 2002.
The Status Sydrome by Michael Marmot 2004.
Why Zebras Don't get Ulcers: A Guide to Stress-Related Diseases and Coping. Robert Sapolsky, 2004.