Editorial
As of January 1, 2014, the global population was more than 7·1 billion, and growing. With continued growth comes increasing population density and more people live in urban areas than ever before. In 1990, less than 40% of the population lived in cities; as of 2010, this figure was 50%, and in 2050, it is projected to be 70%. Planners, policy makers, and architects worldwide will be continuously challenged to innovate efficient, costeffective ways to use transport, space, and recreation areas in cities. In light of accumulating evidence, it is now imperative that they also consider the important relation between the built environment and metabolic health. Obesity, type 2 diabetes, and other non-communicable diseases are rapidly increasing in prevalence in both rural and urban areas. But it is in urban areas—with their increasing population density—that planners and policy makers have the greatest opportunity to influence health by developing and promoting effective use of a healthy built environment. But what makes cities healthy? The built environment comprises anything modified by people, including residences, workplaces, transport infrastructures, pollution, and access to food, hydration, amenities, and green space—the design and selection of which have varying effects on different aspects of health. In particular, a growing body of evidence shows that an environment that promotes physical activity has a substantial preventive effect on obesity and type 2 diabetes. Booth and colleagues presented data at the 74th American Diabetes Association meeting showing that neighbourhoods in Ontario, Canada, that are conducive to walking are associated with decreased diabetes risk; hazard ratios ranged from 0·72 (95% CI 0·67–0·78) to 0·93 (0·91–0·94), depending on the urban area surveyed. Another study done in Australia suggests that preserving and promoting green space in urban areas also reduces type 2 diabetes risk: the risk was 12% lower in residential neighborhoods with more than 40% green space compared with those neighbourhoods that were less green. Thus, destroying green space for housing—a much-debated strategy to cope with increasing population density in some cities—is the antithesis of healthy urban planning. Health in the urban environment is not affected by physical activity alone. Exposure to air pollution has been linked with heart failure and mortality, and might www.thelancet.com/diabetes-endocrinology Vol 2 July 2014
also increase the risk of diabetes. Life in urban areas is associated with a fast-paced lifestyle linked with high stress levels and lower sleep duration or quality, which are contributing factors to many chronic diseases including type 2 diabetes. Advances in green technologies mean that urban areas are becoming less polluted, but reducing stress and promoting better sleep through modulation of the built environment are more difficult goals. The fact that physical inactivity is the fourth leading cause of global mortality means that focusing on this problem is probably the most direct means by which the built environment can positively affect metabolic health. We are far from having a clear understanding about the effects of the multifactorial built environment on health. Study design and data collection are particularly challenging in this area. Components of the environment are often studied in isolation, but it is undoubtedly the collective effects of the built environment that are important in reality. It is difficult to draw parallels between studies conducted in different countries, owing to large differences in culture, climate, and socioeconomic factors. Moreover, data from many low-income and middle-income countries—where population density in urban areas is increasing at the fastest rate—are scarce but urgently needed. In high income countries, where there is more evidence about the effects of the built environment on health, this has been incorporated into urban planning only minimally thus far. In these countries, planners, policy makers, and architects must harness their potential and prioritise sustainable development plans that benefit metabolic health, and physical activity in particular, in urban areas. However, many nuances remain unexplored, and new research must be framed in a manner such that results can be readily translated into new policies and plans. Funders must also recognise the importance of the built environment as a preventive opportunity, and strongly support evidence-based planning initiatives. Such initiatives could synergise with proposed changes to the food industry or taxing of unhealthy foods to substantially curb the epidemic of obesity and diabetes in population-dense areas. With a firm foundation of evidence on both sides of this equation, the bottleneck now is at the level of implementation. ■ The Lancet Diabetes & Endocrinology
Atlantide Phototravel/Corbis
Harnessing cities for metabolic health
For the Lancet Commission Shaping Cities for Health see http://www.thelancet.com/ commissions/healthy-cities For the Avi Friedman profile see In Focus Lancet Diabetes Endocrinol 2014; 4: 278 For more on the proportion of the global population living in cities see http://www.who.int/ gho/urban_health/situation_ trends/urban_population_ growth_text/en/ For more on walkable neighbourhoods and the prevalence of type 2 diabetes see http://www.diabetes.org/ newsroom/press-releases/2014/ do-walkable-neighborhoodsreduce-obesity-and-diabetes. html For more on green space and type 2 diabetes risk see Diabetes Care 2014; 37: 197–201 For more on air pollution and heart failure see Articles Lancet 2013; 382: 1039–48 For more on air pollution and mortality see Articles Lancet 2014; 383: 785–95 For more on air pollution and diabetes see Eur J Epidemiol 2014; 29: 231–42 For WHO physical inactivity and global mortality statistics see http://www.who.int/ dietphysicalactivity/pa/en/
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As of January 1, 2014, the global population was more than 7·1 billion, and growing. With continued growth comes increasing population density and more people live in urban areas than ever before. In 1990, less than 40% of the population lived in cities; as of 2010, this figure was 50%, and in 2050, it is projected to be 70%. Planners, policy makers, and architects worldwide will be continuously challenged to innovate efficient, costeffective ways to use transport, space, and recreation areas in cities. In light of accumulating evidence, it is now imperative that they also consider the important relation between the built environment and metabolic health. Obesity, type 2 diabetes, and other non-communicable diseases are rapidly increasing in prevalence in both rural and urban areas. But it is in urban areas—with their increasing population density—that planners and policy makers have the greatest opportunity to influence health by developing and promoting effective use of a healthy built environment. But what makes cities healthy? The built environment comprises anything modified by people, including residences, workplaces, transport infrastructures, pollution, and access to food, hydration, amenities, and green space—the design and selection of which have varying effects on different aspects of health. In particular, a growing body of evidence shows that an environment that promotes physical activity has a substantial preventive effect on obesity and type 2 diabetes. Booth and colleagues presented data at the 74th American Diabetes Association meeting showing that neighbourhoods in Ontario, Canada, that are conducive to walking are associated with decreased diabetes risk; hazard ratios ranged from 0·72 (95% CI 0·67–0·78) to 0·93 (0·91–0·94), depending on the urban area surveyed. Another study done in Australia suggests that preserving and promoting green space in urban areas also reduces type 2 diabetes risk: the risk was 12% lower in residential neighborhoods with more than 40% green space compared with those neighbourhoods that were less green. Thus, destroying green space for housing—a much-debated strategy to cope with increasing population density in some cities—is the antithesis of healthy urban planning. Health in the urban environment is not affected by physical activity alone. Exposure to air pollution has been linked with heart failure and mortality, and might www.thelancet.com/diabetes-endocrinology Vol 2 July 2014
also increase the risk of diabetes. Life in urban areas is associated with a fast-paced lifestyle linked with high stress levels and lower sleep duration or quality, which are contributing factors to many chronic diseases including type 2 diabetes. Advances in green technologies mean that urban areas are becoming less polluted, but reducing stress and promoting better sleep through modulation of the built environment are more difficult goals. The fact that physical inactivity is the fourth leading cause of global mortality means that focusing on this problem is probably the most direct means by which the built environment can positively affect metabolic health. We are far from having a clear understanding about the effects of the multifactorial built environment on health. Study design and data collection are particularly challenging in this area. Components of the environment are often studied in isolation, but it is undoubtedly the collective effects of the built environment that are important in reality. It is difficult to draw parallels between studies conducted in different countries, owing to large differences in culture, climate, and socioeconomic factors. Moreover, data from many low-income and middle-income countries—where population density in urban areas is increasing at the fastest rate—are scarce but urgently needed. In high income countries, where there is more evidence about the effects of the built environment on health, this has been incorporated into urban planning only minimally thus far. In these countries, planners, policy makers, and architects must harness their potential and prioritise sustainable development plans that benefit metabolic health, and physical activity in particular, in urban areas. However, many nuances remain unexplored, and new research must be framed in a manner such that results can be readily translated into new policies and plans. Funders must also recognise the importance of the built environment as a preventive opportunity, and strongly support evidence-based planning initiatives. Such initiatives could synergise with proposed changes to the food industry or taxing of unhealthy foods to substantially curb the epidemic of obesity and diabetes in population-dense areas. With a firm foundation of evidence on both sides of this equation, the bottleneck now is at the level of implementation. ■ The Lancet Diabetes & Endocrinology
Atlantide Phototravel/Corbis
Harnessing cities for metabolic health
For the Lancet Commission Shaping Cities for Health see http://www.thelancet.com/ commissions/healthy-cities For the Avi Friedman profile see In Focus Lancet Diabetes Endocrinol 2014; 4: 278 For more on the proportion of the global population living in cities see http://www.who.int/ gho/urban_health/situation_ trends/urban_population_ growth_text/en/ For more on walkable neighbourhoods and the prevalence of type 2 diabetes see http://www.diabetes.org/ newsroom/press-releases/2014/ do-walkable-neighborhoodsreduce-obesity-and-diabetes. html For more on green space and type 2 diabetes risk see Diabetes Care 2014; 37: 197–201 For more on air pollution and heart failure see Articles Lancet 2013; 382: 1039–48 For more on air pollution and mortality see Articles Lancet 2014; 383: 785–95 For more on air pollution and diabetes see Eur J Epidemiol 2014; 29: 231–42 For WHO physical inactivity and global mortality statistics see http://www.who.int/ dietphysicalactivity/pa/en/
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