Houses in the still relatively dense London suburb of Willesden. Suzanne Plunkett/Reuters

A U.K. study finds a clear connection between density and obesity—and even rural areas fare better than suburban ones.

Living in a more densely built area significantly lowers your risk of obesity. Such is the unavoidable conclusion of a new survey of British cities that compares obesity rates with housing density. The study, carried out by specialists at the universities of Oxford and Hong Kong, found that obesity rates were markedly lower in areas where homes were more tightly clustered.

This might not come as a shock, given the long touted health benefits of walkable neighborhoods. What makes the study, published in medical journal The Lancet and first covered by Reuters, truly groundbreaking is its sheer scale, collating data for over 419,000 respondents in 22 British metropolitan areas over a period of four years. While it would be mistaken to assume that observations made in the U.K. could apply everywhere, they make one thing clear: Residents’ health is highly likely to improve when sprawling suburbs are made more dense. As the graph below details, it also breaks ground by matching obesity levels with specific rates of housing density.

Reprinted from The Lancet Planetary Health, Copyright (2017), with permission from Elsevier

The graph’s three tables cover, from top to bottom, BMI, waist circumference, and whole body fat mapped against the housing density for a given neighborhood. It is controlled for age and gender, so, for instance, younger women living in dense and non-dense areas are being compared with each other rather than people from a different group.

The worst obesity rates, the study finds, are among British people who live in areas with 1,800 homes per square kilometer (around 4,662 dwellings per square mile). That’s close to the typical density for London’s more sprawling, low-density outer boroughs, whose average density of 1,590 dwellings per square kilometer is brought down by the large areas of parkland and small areas of farmland still within the city limits. Below this density, obesity rates actually start to fall somewhat, the study finding that the lack of walkability for British people living in sparsely populated areas was compensated for by a relatively active lifestyle.

Even people who live in very sparsely populated areas still had considerably higher levels of obesity than people who live in densely built cities. There's a cut-off point around 3,200 dwellings per square kilometer: above that, people have consistently lower levels of obesity than their counterparts in very sparsely populated areas. (The U.K. currently recommends this level of density for all newly built districts.)

Moving further up the density scale, people living at the higher densities typical for inner London (which has an average of 4,500 dwellings per square kilometer) have a notably lower average BMI, whole body fat, and waist circumferences that gives them a clear edge health-wise over people living in more sprawlingly developed areas of Britain.

So why is obesity less common in densely built areas? The obvious answer is walkability. When amenities are within easy walking distance there is, quite simply, more incentive to walk to them, while densely built environments can also de-incentivize driving because of their congestion and limited parking. The study’s authors also suggest another factor.

“A highly compact dense residential environment might act as a proxy for enhanced community social capital and support,” the report says. “The intangible stress-relieving potential of centrality, accessibility, and social capital needs to be further examined in view of their protective effects on obesity.”

In other words, being at the heart of things, being able to get around easily, and having more opportunities to build wider social networks might actually boost wellbeing in itself by making life easier, as well as encouraging people to leave their homes more.

Despite its impressive size, the study’s findings have some potential limits to their relevance that the authors themselves acknowledge. First, it may be the case that people actively seeking a sedentary lifestyle choose to move to less dense areas. The study counterbalanced this hypothesis by comparing obesity levels among newly arrived suburbanites and long-term residents. They found no difference between the two groups, implying (but, vitally, not proving) that the suburbs were not attracting people more prone to obesity.

The other limit is an interesting question that remains unanswered: Is there an upward limit after which home density becomes so great that it actually encourages obesity? The study found no upward limit, but it used data only from the U.K., where densities never reach the extremely high levels of some cities in South and East Asia.

What the study does suggest is nonetheless extremely important. If obesity drops as homes cluster more closely together, there is a clear public health argument for densifying the suburbs, providing that densification is mixed-use and thus also comes with a denser cluster of shopping, entertainment, and other amenities that make walking desirable.

The current recommended minimum density for new development of housing in the U.K. of 3,200 homes per square kilometer might ensure that future neighborhoods will have a layout somewhat less conducive to high obesity, though we could do better. Most British suburbanites nonetheless live—and will continue to live—in areas whose considerably lower density is often frozen by local planning laws and resistance from residents who fear drops in property prices or possible congestion. It’s possible that as the understanding that these environments are not especially healthy permeates through society, Britain’s lower density neighborhoods might prove more amenable to the home-building the country so desperately needs.

CORRECTION: An earlier version of this article mistakenly referred to the  number of dwellings per acre when it should have cited the number of dwellings per square mile. This has been corrected.

This article is part of a series highlighting the themes of CityLab Paris, a convening of urban leaders.

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