There's plenty of data showing that urban living can be healthier for very non-mysterious reasons. Recently I saw this image:
While the numbers are hard to see on this image, what does jump out quite clearly is the balanced use of transportation modes in downtown Toronto, and the gross imbalance outside downtown.
If subways are not going to lace across the entire GTA (as a real transit system should), then the bus and light rail system and service, in lieu of subways, must be competitively good at moving lots of people quickly, in order to reduce dependence on cars - and the problems created by that dependence (pollution, poorer health, etc.) - outside the downtown area.
The graph above illustrates clearly that there’s no fooling people – buses and light rail in Toronto have thus far failed to provide an equivalent degree of service beyond subways, beyond downtown, which is a primary contributor to Toronto having the longest average commute (yes, longer than Los Angeles, longer than New York City) and choking gridlock that costs the region upwards of $5 billion each year in lost productivity.