How we plan neighborhoods can shape the health of entire communities. When more than half the world now lives in urban areas, it's more important than ever to design streets and parks conducive to walking, running, and cycling.
A review of large, population-based studies describes numerous ways walkable, activity-friendly cities are linked to improved metabolic health.
A study of 14 cities in 10 countries, for instance, found residents living in neighborhoods that were easily walkable and had transit options other than driving got nearly 90 minutes of extra exercise per week under their belt compared to the least activity-friendly neighborhoods.
The authors of the review admit that some bias might be sneaking into these results. Fitter individuals, for instance, might choose to live in areas that suit their interests. On the other hand, poor walkability in some neighborhoods might reflect the link between socioeconomic status and health more than anything else.
Nevertheless, studies that examined how individual activity changes when people move houses also found evidence that greater access to shops, paths, parks, and public transport can lead someone to perform upwards of 16 additional minutes of physical activity per week.
Although studies comparing physical activity and urban design are important, another potentially more important line of inquiry is how this extra activity impacts diabetes, hypertension, and cardiovascular health.
One study in Canada, which included more than 30,000 participants, found the prevalence of obesity in a highly walkable area was as many as 10 percentage points lower when compared to one with low walkability.
An even larger study of 1.1 million healthy adults found the likelihood of pre-diabetes developing over eight years was 20 percent higher in less walkable neighborhoods.
Some initial research suggests there might even be an association between an area's walkability and markers of glycemic control and insulin resistance. However, the reviewers say few of these studies adequately controlled for socioeconomic status and race.
Markers of cardiovascular health, on the other hand, appear more clearly impacted. A population-based study in Canada, for instance, found moving from an 'unwalkable' neighborhood to a highly walkable one was linked to a 54 percent reduction in the development of high blood pressure over the course of a decade.
Other population-based studies in Australia, the United States, and the United Kingdom largely support these results.
In the end, the authors of the review conclude that a large number of globally representative studies suggest denser, more walkable cities can help improve the metabolic health of a community in a "clinically meaningful" way.
That said, further research is still needed, especially when teasing apart other factors that can also influence public health.
"Although it is convenient to discuss the built environment "s impact on health in isolation, there is a complex interplay between environmental exposures," the authors of the review note.
"Neighborhood socioeconomic conditions, food environments, air pollution levels, and natural features, like green space, may independently influence metabolic health and must be considered when isolating the effects of the built environment."
Some studies, for instance, have found access to green spaces can improve public health, although whether this is through physical exercise or something else remains to be seen.
There's also the possibility that adding more green spaces to a city can reduce local air pollution, which could also improve a population's physical health and well-being.
Human behavior isn't easy to predict or manage, but it seems like when people are offered the opportunity to get outside and move, they jump at the chance.
The study was published in Endocrine Reviews.