Respiratory Health and Cities

We practice medicine in an ever-changing world. An increasing proportion of the global population lives in cities and other urban areas. What does this mean for the respiratory health of those living in cities and their clinicians?

The challenges of living in rural areas have been well described and center on poor access to expert health care (1) because of fewer providers; workforce shortages; greater travel distances; and, therefore, increased costs. The greater likelihood of proximity to expertise in cities masks several problems that are particularly relevant to respiratory health. These need specific consideration if we are to advocate for appropriate health care for all. Some of these problems are shared across high-income countries and low- and middle-income countries (LMICs), but the greatest challenges relate to rapid urbanization in LMICs.

In this Viewpoint, we discuss the challenges of urban respiratory health. We argue that our community must lobby for better respiratory health in cities to reduce the future burden of disease.

Demographic Transitions

The World Health Organization (WHO) has reported that 55% of the world’s population currently lives in urban areas, with an increase to 68% expected by 2050 (2). The proportion of the population in rural compared with urban settings varies by country. In an examination of the two most populous countries, for example, the urban:rural split yields 64% rural in India but 64% urban in China. Population growth in cities is mostly driven by migration to seek economic opportunities, with migrants in LMICs often living in informal settlements (3). Urbanization can bring economic benefits, but uncontrolled growth brings challenges in the provision of housing and basic services such as sanitation and electricity, health care and transportation. Health inequity may, therefore, be greatest in urban areas (2).

The WHO “Triple Threat”

The WHO describes a triple threat to health in urban environments comprising noncommunicable diseases (NCDs), infectious diseases, and injuries and violence (2). Major drivers include poor air quality, lack of clean drinking water, poor sanitation, overcrowding and poor housing, wide availability of junk foods, and poor transport infrastructure without safe spaces for physical activity. With susceptibility to natural disasters and climate change, the health of our cities is also intimately linked with planetary health. How do the WHO triple threats relate to respiratory health?

Chronic Respiratory Disease

Poor air quality in urban areas is a major driver of chronic respiratory disease in cities, including contributions from traffic pollution, industry, and domestic use of solid fuels. However, individual exposures and behavior transcend simple classification of chronic respiratory disease risk by urban compared with rural environments. Exposure to indoor tobacco smoke remains a contributor in cities where this is not banned. Air pollution also contributes to the increased risk of other NCDs, such that respiratory disease is a frequent component of multimorbidity. Addressing urban air quality is critical to progress toward achieving United Nations Sustainable Development Goal 3.4 to reduce premature mortality from NCDs by one-third by 2030.

To take chronic obstructive pulmonary disease (COPD) as an example, the prevalence varies markedly by setting. U.S. data suggest a higher prevalence in rural areas (4), perhaps associated with increased use of solid fuels. In general, the prevalence of COPD is higher in rural areas of LMICs, too (5), but the importance of local context is illustrated by the particularly high prevalence of COPD in urban industrial workers (6). Relationships between urban and rural environments with asthma prevalence and control are similarly complex.

Respiratory Infections

Urban living is often associated with crowding and poor sanitation, both of which contribute to the excess incidence of infectious diseases. The interplay between NCDs and acute infections is a neglected area, relevant to chronic respiratory disease in relation to exacerbations.

Common cold viruses are the most common cause of airway disease exacerbations, and there are conflicting data on the incidence of the common cold and exacerbations in cities compared with rural regions. Both COPD (7) and asthma (8) exacerbations are associated with pollutants. Exacerbation risk in urban environments is likely dominated by transmission of respiratory viruses and air pollution.

In general, tuberculosis is more common in urban areas that are associated with overcrowding, poverty, and inadequate housing. A meta-analysis has reported that long-term exposure to airborne pollutants is associated with a higher risk of incident tuberculosis (9). Overcrowding also associates with increased transmission of influenza and coronavirus disease (COVID-19).

Mitigations to reduce the risk of acute respiratory infections in urban populations must focus on reducing risk factors relating to overcrowding, socioeconomic disadvantage across the life course, and improving air quality.

Injuries and Violence

Although the WHO focuses on interpersonal violence and traffic accidents, cities are also a target of terrorist activities. The attacks on September 11, 2001, highlighted the acute and long-term morbidity associated with respiratory exposures in these contexts (10). Urban areas can also experience industrial disasters, such as in Bhopal, India, leaving a legacy of chronic respiratory disease. Real or perceived risk of violence can limit the value of parks and green spaces in which to exercise. Improvement in the safety of such facilities is, therefore, an investment in respiratory health. Psychosocial stress may exaggerate the effect of pollutants and living with chronic respiratory disease. The absence of safe, unpolluted spaces in which to exercise makes it harder to remain active, and this is particularly important for those living with chronic respiratory disease.

The Health of Our Cities and Planetary Health

Given that cities account for >60% of greenhouse gas emissions (2) and consume two-thirds of the energy, the health of cities is intimately linked with the health of the planet. The WHO has highlighted that urban populations are particularly vulnerable to climate change (2), with temperatures 3–5°C higher than in surrounding areas because of “heat island” effects resulting from expanses of concrete. This is relevant to chronic respiratory disease, with greater COPD exacerbation risk at extreme temperatures.

Moving Forward: Healthy Planet, Healthy Cities, Healthy Lungs

The WHO has an increasing focus on urban health (2), including the Healthy Cities initiative, which is “conceived with the goal of placing health high on the social and political agenda of cities by promoting health, equity and sustainable development through innovation and multisectoral change” (11). The emphasis on multisectoral change is critical, including healthcare professionals and policymakers working closely with those who work in the built environment, urban planning, transportation, environmental management, and emergency preparedness fields. Examples of air quality mitigation interventions from the cities in which we work are described in Figure 1 and include environmental legislation, societal education, cleaner energy and transportation, and public green spaces.

Figure 1.

Air quality mitigation interventions for selected global cities.

Conclusions

Urban living brings challenges to respiratory health. Air pollution, overcrowding with the transmission of respiratory pathogens, social disadvantage, lack of ability to safely exercise, and heat islands all increase the risk of acute and chronic respiratory disease. With global warming and demographic transitions to more people living in urban areas, we cannot stand by. To reduce the future burden of lung disease in those living in urban environments, we urgently need a response that is coordinated across sectors and sufficiently disruptive to transform the future respiratory health of cities while being sustainable and cost-effective to implement.