In “Congested cities vs. sprawl makes you fat: unpacking the health effects of density,” an essay that recently appeared in Town Planning Review, Ann Forsyth, a professor of urban planning at the Harvard Graduate School of Design who is a Joint Center faculty affiliate, explores a complex relationship that has been at the heart of many major planning initiatives.

Forsyth, whose research was partially supported by the Joint Center’s Student Research Support Program, writes that since the contemporary version of urban planning emerged in the nineteenth century, the field has been concerned with how changes in density might address a variety of problems, including many related to human health.

The essay, which initially was delivered as the 15th Annual Abercrombie Lecture at the University of Liverpool (honoring Sir Patrick Abercrombie, a leading British planner of the 20^th century), goes on to note that in the first part of the 20^th century, planners sought to reduce densities as a way to address problems associated with urban slums. More recently, however, many planners have pushed for increased densities as a way to address problems such as obesity, social isolation, and sustainability. These shifts, she writes, are not just changes in planning fashions but stem from an underlying situation where “the relationships between health and places vary greatly according to health topic, population group and type of density from housing to parks.”

The essay unpacks these issues, first by clarifying the concept of density and then by exploring both perception of – and data on – the ways that density can be used to help create healthy cities and regions. This review, she notes, highlights that fact that “while there is definitely something in the connection between environmental features, such as density and health, these connections are complex.”

She concludes with a detailed discussion about how density can affect health outcomes for frail seniors.  This review, she notes, shows that people can live healthy lives at a variety of densities but that the kinds of health advantages differ. For example, lower building densities can help with air quality and higher population densities help with access to services.

Given the many and complex ways that density can affect health, she notes, planners must be “quite sophisticated about using density as a solution” to health-related issues. Doing so, she explains, requires a nuanced approach that is sensitive to non-linear relationships, differing effects across populations, and diverging density costs and benefits. Planners who ignore these subtleties, she adds, run the risk of creating policies that have serious unintended negative consequences.