This trailer for "Unnatural Causes," a four-part documentary series that aired on PBS and is currently streaming -- in excerpts -- on YouTube and the series' own Website, asks a simple question: Is inequality making us sick?

The answer, as the documentary reveals, is far more complex than the question.

Larry Adelman, the series' executive producer, writes in a statement:

"It's not just the poor who are sick. Even the middle classes die, on average, almost three years sooner than the rich. And at every step down the socio-economic ladder, African Americans, Native Americans and Pacific Islanders often fare worse than their white counterparts.

Our international health status has fallen radically in the last few decades. In 1980, we ranked 14th in life expectancy; by 2007, we had fallen to 29th. Our infant mortality rate lags behind 30 other countries. And illness now costs American business more than $1 trillion a year in lost productivity.

Healthy behaviors, molecular research, and of course, universal health care are all important. But evidence suggests they miss the most vital factor of all: how the social circumstances in which we are born, live and work can get under our skin and disrupt our biology as surely as germs and viruses."