Salon.com has an article which describes how people who live in sprawling suburban areas are more likely to have health problems such as high blood pressure, arthritis, headaches, and breathing difficulties, even after controlling for many other factors. It appears that the direct cause is people in sprawling suburbs drive more while those in more compact cities walk more.

That sounds plausible enough but I would like to know, among all people who live in more compact cities such as NYC, SF, Boston, Seattle, and Portland (as cited in the report), do people who live where the population size is smaller or less dense (i.e., Portland & Seattle) report fewer health problems than those in cities with large populations and densities (i.e., NYC, SF, or Boston)?