Counterintuitive as it may seem, living in city centres may actually be good for your health. Especially for your weight.

A new research carried out in British cities shows that suburban residents are at higher risk of obesity compared to their inner-city counterparts, for whom chances of being obese are significantly lower.

This may not strike you as particularly surprising since the association of obesity with residential density had already been shown by previous international studies. But now this group of researchers at the Oxford University and the University of Hong Kong (UHK) found something that not only sets their study apart from others but could also change how cities are planned in the future.

One of the strengths of the study, published in the medical journal The Lancet, is the size and diversity of its dataset. For the analysis, the authors used UK Biobank to draw a sample of 419 000 individuals — adult men and women aged between 37 and 73 years — from 22 cities across the UK. The data were collected over a period of four years (2006 to 2010).

But beyond its sheer scale, the one thing that really makes this study stand out is that, for the first time, a level of residential density for sustaining healthy weight has been determined.

What this means is that the researchers were able to identify a turning point, a limit or threshold, after which density (the number of houses in a given area) begins to decrease the odds of obesity. The turning point, it turns out, is 1800 homes per km².

Why is this important? Well, the answer is because it provides “a metric”, a way of estimating the effect of housing policy and urban planning on obesity.

Meaning that with this tool politicians can now anticipate the impact that urban planning policies might have on people’s health. This also means that public opinion can now be more aware of those implications and better equipped to hold their representatives accountable for their political decisions.

“If we can convince policy makers that this is a public health opportunity, we can build well-designed communities, and in the long term, you have made a big difference in health outcomes,” assistant professor at the University of Hong Kong and co-author of the paper, Chinmoy Sarkar, told the Thomson Reuters Foundation.

The denser, the healthier

Overall, the research matched obesity rates with residential density and found that the two are intrinsically and inversely connected. More importantly, it shed some light on the ideal levels of density for sustaining healthy weight.

Here’s what the Oxford University and the UHK researchers found: at 1800 houses per km², obesity rates reach the peak (point ‘A’ on the graph below). People living in this density range had the highest values in all three adiposity indicators: body-mass index (BMI), waist circumference and whole body fat. Plus, they had the lowest rates of exercise — an explosive combination which raises the risk of obesity and obesity-related diseases, such as diabetes, cardiovascular disease and cancer.

Association between adiposity and housing density. © 2017 The Lancet Planetary Health

In the UK, where the study was conducted, this typically corresponds to areas experiencing suburban sprawl. According to the authors, the prevalence of obesity in such areas is a well-known issue and can be attributed to the usual suspects: a sedentary lifestyle, long commutes to work by car or public transport, and low activity levels.

Luckily, things look a bit brighter for residents above and below this density range. Even in scattered semi-urban neighbourhoods—where there are often private outdoor spaces that encourage physical activity— residents had lower rates of obesity.

Moving up the density ladder above the 1800 km² barrier, obesity markers (BMI, waist circumference, and body fat) start to significantly fall.

It is in areas with 3200 homes per km² or more, however, that the protective effects on obesity become most pronounced. This density range corresponds to urban suburbs, compact inner suburbs, and city centres, which usually offer more infrastructures, retail, walking paths and other attractions, as well as proximity to work.

The Suburbs by Arcade Fire. Arcade Fire/Youtube


Building the case for built-up cities

So when it comes to preventing obesity, living in built-up areas such as city centres does seem to pay off. And what really makes the difference, the authors reckon, is the walkability factor.

“As cities get more and more compact, they become more walkable. In denser residential areas, they are better designed and more attractive destinations. We are less dependent on our cars and use public transport more”, Chinmoy Sarkar said.

Moreover, cities that offer greater access to places and services require less mobility, according to transportation and mobility researcher, Jorge Pinho de Sousa.

“Mobility is somehow a secondary matter because the development of cities and metropolitan areas should imply that people can have access to a set of goods and services without having to travel”, he told the City of Future last year in an interview.

Pinho de Sousa, who is also a professor at FEUP (Engineering Faculty of the University of Porto) and MIT-Portugal, said that urban mobility patterns are already starting to shift towards soft modes of transport, in other words, walking and cycling.

The way he sees it, new habits of life and changes in the labour market, such as an increasing offer of remote jobs, could help to explain this incipient change. Which, in his opinion, “must be accompanied by the creation of cities with multiple centres, with green areas and pleasant spaces that encourage people to stay there.”

So if walkability increases and obesity falls in areas where homes are packed more tightly together, scientists argue, this should persuade politicians and urban planners to promote the suburbs densification.

The Oxford University/UHK research even points to a number of measures that could contribute to healthy densification. Creating affordable urban housing, building compact mixed-use urban developments, investing in public parks and green spaces, and design to reduce exposure to road proximity are among the recommendations.

Besides the obvious effect on weight outcomes, the study suggests that a more built-up environment could also benefit our well-being.

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

As to the reach of the observations made in a UK context, the authors note that despite the confidence such a large-scale dataset provides, their findings may not apply to countries where cities have very different population densities.

High-density areas, such as those encountered in Honk-Kong, China and India, would likely reveal different turning-points beyond which residential density could sustain healthy weight. Therefore, they stress the importance of performing country-specific research. michael kors tasche

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