The Health Effects of Motorization

The world is undergoing a rapid transition in population health, away from mostly infectious disease in children to non-communicable diseases (NCDs) and injuries that affect adults [1,2]. The global health transition is strongly tied to levels of industrial development in lowand middle-income countries. NCDs and injuries now comprise 94% of all deaths in China, 65% in India, and 34% in sub-Saharan Africa [2]. The study by Christopher Millett and colleagues, in this week’s PLOS Medicine [3], paints a vivid picture of the sources of the transition to NCDs and injuries. Their paper highlights the shift in health risks that accompany migration from rural to urban settings, reporting that rural dwellers who migrate to cities have worse cardiovascular outcomes than their nonmigrant siblings, partly due to a shift to private motor vehicles and reduced physical activity, especially reduced bicycling. While there is strong evidence from highincome countries linking physical inactivity to major NCDs, including coronary heart disease, type 2 diabetes, and breast and colon cancers [4], Millett and colleagues present important evidence from a rapidly developing economy. Of course, declines in physical activity are not the only risks faced by the urban migrants in their study. These migrants are also exposed to higher concentrations of urban air pollution and possibly higher risks for injuries in motor vehicle crashes. Urbanization is one of a cluster of interconnected global forces shaping people’s physical activity and their exposure to air pollution and injuries [5]. These megatrends include increases in personal motorization, population aging, food consumption, globalization of production, and electronic entertainment, among others. Public health practitioners are faced with the challenge of managing the production of health within this context. Furthermore, policy and planning decisions taken now will have long-term effects: whether countries in Asia and Africa build high-density mixed-use cities or choose low-density sprawl, for example, or, whether countries choose to motorize via motorcycles, cars, or public transit or choose transport through active modes. These decisions will determine levels of physical activity, vehicular emissions, and crash risks, and thus influence NCD and injury rates for future generations of urban dwellers.