Why?

Suburban sprawl is "sickening." Its "effects add up." "Study links health issues to metropolitan sprawl":

The increase in health problems is presumably due to the fact that sprawl discourages physical activity, increasing the chances of being overweight or obese. In addition, sprawling communities tend to have more air pollution, [RAND Corporation senior economist Roland] Sturm said.

Sturm and colleague Deborah Cohen analyzed data collected by the Healthcare for Communities, a survey that in 1998 and 2001 questioned a nationally representative sample of 8,686 adults in 38 areas about a spectrum of health issues. The researchers then examined whether there was an association between 16 health problems and the amount of sprawl where participants lived, using a standard scale that includes such measures as population density, street patterns and proximity of businesses and workplaces to residences.

. . . . . . . .

People living in areas that scored highest on the sprawl scale reported the most problems, with the unhealthful effects appearing to disproportionately affect the poor and the elderly. The association was particularly significant with arthritis, respiratory problems such as asthma, stomach problems, headaches and urinary tract infections.

Those living in very spread out places, such as Atlanta, had about 100 more health problems per 1,000 people than those living in areas that were less so, such as the Greensboro-Winston Salem area of North Carolina.

Although some researchers have speculated that the social isolation that can occur in sprawling communities may also lead to more mental health problems, such as depression, the new study failed to find that link.

Although later in that particular article:

Peter Gordon, a professor in the school of policy, planning and development at the University of Southern California in Los Angeles called the study "junk science." The areas studied, for example, are so large they could not distinguish important neighborhood differences, he said.

Nevertheless, the results seem a little surprising, since, for example, you might think the air is clearer in neighborhoods less dense, as high densities generate a lot of car traffic and therefore a high level of emissions. But then, it seems this study focused on metropolitan areas, not neighborhoods (sorry, I haven't read the actual study); perhaps the outer sprawl somehow degrades the health of the entire area, including the "nonsprawl" inner city, and/or health of the outer sprawl's population is bad enough that, statistically, it simply brings down the metropolitan area's average level of health.

If the notion that inner city-style nonsprawl is healthier than suburban/exurban sprawl is true, what does that mean for a place like the Bay Area, in which housing is terribly expensive inward but quite affordable outward (except in terms of the car commute)? The "haves" get good health, while the "have-nots" get bad health? I suppose that's nothing new, considering health care itself is rather costly, but it's an aspect to consider.