Over half of the world’s population – 4.2 billion people – live in cities.
This number is expected to rise, with 68% of the global population estimated to live in urban areas by 2050.
Among the world’s megacities – defined as urban areas with more than 10 million inhabitants – Tokyo, Japan is the largest, with 37 million citizens.
It is followed by Delhi, India (29 million) and Shanghai, China (26 million).
In the UK, after several decades of rural-to-urban migration, 83% of people live in urban environments – and London has become the first European megacity.
The detrimental effects of urban living on physical health have long been recognised, including higher rates of cardiovascular and respiratory disease.
More recent, however, is the revelation that urban living can also have adverse effects on mental health.
The risk of developing depression – the most prevalent mental disorder in the world, characterised by low mood and feeling helpless – is 20% higher in urban dwellers than those who live outside the city.
Meanwhile, the risk of developing psychosis – a severe psychiatric disorder associated with hallucinations, delusions, paranoia and disorganised thought – is 77% higher in urban than rural dwellers. The risk of developing generalised anxiety disorder, a state of mind characterised by feeling anxious and a sense of impending danger or panic, is also 21% higher in urban than rural dwellers.
Critically, the longer you spend in an urban environment during childhood and adolescence, the higher your risk of developing mental illness in adulthood.
This “dose-response” association provides indirect support for a causal relationship between urban living and mental illness.
Support for these epidemiological findings comes from the brain sciences.
In a pioneering study in 2011, researchers measured neural activation during a stress-inducing task.
As expected, all participants showed increased neuronal activation within the limbic system – a network of regions that plays a key role in our day-to-day regulation of emotion. Within this network, neural activation in the amygdala – the “fight or flight” centre of the brain – correlated with the size of the city in which an individual resided at the time of the experiment.
And neural activation of the perigenual anterior cingulate cortex – a region implicated in the processing of social stress – correlated with how long a participant had lived in a city during their childhood.
Intriguingly, other studies have shown similar alterations in people who have high genetic risk of developing psychiatric disorders. This supports the notion that urban living causes changes within a network of regions implicated in the development of mental illness.
Taken together, epidemiological and neuroscientific studies provide converging evidence that, indeed, people who live in urban areas are at greater risk of mental health problems. So which specific factors within the urban environment increase the risk of developing such problems?
Epidemiological studies have identified a large number of factors. Some of these highlight potential problems in the built environment, such as reduced access to green spaces and high levels of noise and air pollution.
Others pertain to the social environment, such as loneliness, perceived and actual crime, and social inequalities.
The detrimental effects of urban living on physical health have long been recognised, including higher rates of cardiovascular and respiratory disease. More recent, however, is the revelation that urban living can also have adverse effects on mental health. domain.
These studies were based on the collection of a single snapshot per participant, and therefore could not capture the multiple and diverse environments that most people experience throughout the day.
But some new studies are using smartphone technologies to collect multiple measurements as people go about their daily life. Urban Mind, for example, is a citizen-science project which uses a smartphone app to measure the experience of urban or rural living in real-time.
It’s important to recognise that those factors within the urban environment which increase the risk of mental illness are neither intrinsic nor inevitable aspects of urban living.
Instead they are the result of poor planning, design and management, and could be reversed. Which takes us to the next question: could urban living be good for our mental health?
The bright side
While existing research focuses on the negative impacts of urban living on mental health, framing the accelerated urbanisation taking place worldwide as a challenge to humankind, this is an oversimplification of what it means to live in a city for at least three reasons.
First, urban living is a complex, contradictory and difficult to define phenomenon, with little in common between the resident of a deprived suburb and that of a garden city; or between the processes of gentrification and those of inner city decline.
Consistent with this notion, the incidence of depression within urban areas is lower when people have access to high quality housing and green spaces.
Second, we know that all health, and mental health in particular, depends on both nature and nurture. For example, emerging evidence from epigenetics, which examines how the environment affects the expression of our genes, suggests that the impact of urban living depends on our preexisting genetic makeup.
Third, for many people, urban living can bring great benefits to mental health through increased opportunities for education, employment, socialisation and access to specialised care. Moving to a city can be the first step towards the realisation of one’s full potential, and a necessary condition to gain access to communities with similar interests and values.
Ultimately, cities offer a swath of obstacles and opportunities, freedom and captivity, which can challenge as well as nurture us, often at the same time.
A Human Environment
The assurance of food security provided by the First Agricultural Revolution and its subsequent allowance for the exchange of food and ideas, solidified the impetus for high-density human settlements .
Improvements in the amount of food provided per square foot of land meant larger populations could be fed in a relatively small area, entailing that not all individuals were required to take on an occupation of hunting, gathering, or farming .
Anthropological theories tend to accredit the formation of high-density settlements to the natural economic viability of a centralized location where food could be transported, stored, and traded with a breadth of services provided by individuals who have pursued occupational specialties.
The maintenance of this economic viability relies on the positive surplus of these and other benefits over liabilities such as crime and disease.
Whatever the rationale was for our prehistoric ancestors to practice waste management, the separation of unneeded and potentially harmful refuse from daily living spaces has conferred benefits on the security and evolution of societies.
As early as Neolithic times, humans were found to have amassed and separated materials such as mollusk shells, animal bones, debitage, and feces in well-defined dumpsites . The era appears to have marked our ancestors’ first traceable practice of functional space allocation and designation.
The first humans to hone this practice as a conscious process were in theory the first designers and planners. Ancient high-density settlements, hereafter referred to as ‘cities’, were a direct result of an evolution of those conscious processes.
Cities across Africa, Eurasia, and the Americas were constructed with varying systems for aqueducts and sewers to support the population’s needs for water and sanitation.
The summation of these practices continues today, apart from earlier understandings of religious or social taboo, as a component necessary to both public health and urban planning.
A Healthy Environment
Leading health concerns in recent centuries have changed as a direct result of how humans have approached the idea of their occupying a small space together.
Areas with higher population densities were centers of commerce, governance, and other forms of power, and were known foci or catalysts for morbidity. Activities commonly initiated from centers of power, particularly trade and war, expedited the bubonic plague’s spread into Europe and smallpox’s introduction to Mesoamerica and Southeast Asia [4,5,6].
While the etiologies were later fully realized, it was known far beforehand that individuals were exceptionally more likely to contract infectious diseases such as cholera in industrialized cities like London, Liverpool, Chicago, and New York in comparison to the countryside and less-connected, less-industrialized settlements.
Investigations, like those by Valentine Seaman addressing yellow fever in 1795 New York [7,8] and John Snow in 1854 London addressing cholera [9,10], focused on the nature of disease in its geographical context and established the importance of the built environment in disease incidence.
The 18th century had already seen several coastal cities essential to regional and transoceanic trade adopting criteria and protocols for isolating the sick and establishing quarantine at the governmental level .
In these formative years of the practice of public health, it was realized that disease management could be approached with planned and coordinated community action.
Developed countries where public health initiatives first took hold, appear to be the first and most-effective at lowering rates of mortality attributed to communicable and infectious disease [11,12,13].
Where it was once infectious phenomena like tuberculosis, pneumonia, diarrhea, and enteritis that claimed the most American lives, it is now non-communicable diseases that have become the leading causes of death.
These conditions, including ischemic heart disease, stroke, Alzheimer’s, respiratory cancers, and diabetes were once considered to be ‘diseases of affluence’ as they were historically known mainly to afflict industrialized regions with substantial urban populations [14,15].
Following the geographic spread pattern of industrialization, these conditions have become especially prevalent in the latter half of the 20th century in urban populations of developed nations and in urban populations of developing nations in the following decades.
This burden of disease continues to scourge a greater proportion of individuals, regardless of social class, and are becoming widely experienced among those living below the poverty line [16,17,18].
Developments in the practices of sanitation and building code have addressed public health concerns in recent centuries, greatly improving the health conditions of city dwellers [19,20,21].
It was clear by the 1850s that overcrowding, low incomes, and death were interrelated and distinct in the urban settings of industrialized nations . Initial reforms to prioritize urban sanitation and public health were accomplished with the leveraged insight that the wealthy, and thus more politically influential, were threatened by the same health risks that afflicted the poor. New York City’s squalor was a substantiated economic and political liability, mobilizing constituents from all socioeconomic classes to pressure lawmakers into imposing standards for sanitation .
Diverse pressures established guidelines for fire safety, access to utilities and physical accessibility, environmental control, and other necessities. It continues to take varying successions of concerted social movements to influence belief, practice, and legislation, backed by scientific rigor, to address the evolving risks of urban living .
Consummating efforts across disciplines bring attention to relative blinds spots historically found in respective practices. The concreteness of physical illness has fueled the advancement of interdisciplinary cooperation and aided the generation of data, indicating the need to address safety and mental health concerns, apart from the traditional realm of physical health, at an administrative level.
Mental health is now acknowledged to cost the world millions of disability-adjusted life years (DALYs) and underestimated amounts of major financial loss [25,26]. Suicide has consistently ranked among the top 10 causes of death in the United States since 1975 [13,27,28]. Resulting increases in awareness of mental health concerns further generates investment and data to address these concerns.
Nevertheless, public efforts that target mental illness trail behind investments in other health-related and safety issues. The World Health Organization reports neuropsychiatric illness as causing 13% of the world’s burden of disease in a 2003 report, while accounting for about only 2% of total government health budgets .
This discrepancy in policy and investment is associated with the current limitations in technology, deficiencies of data, and an immaturity of awareness with regards to mental illness, as compared to physical illness.
Studies have yet to definitively confirm the proportion of burden of mental illness which urban centers carry when compared to rural areas. Whatever the risk to health or safety there is to be addressed, the urban setting provides an ideal opportunity for policy to deliver relief for the greatest amount of individuals.
A Humane Environment
Urban designers and planners, policymakers, community leaders, and leaders of other specialties have worked to address the risks of living in densely populated communities. The most ambitious of these collaborations result in the tailoring of built environments to prioritize the wellbeing of inhabitants.
The work of building humane environments is not novel in public health praxis. Traffic engineers and ergonomics engineers, among others, have collaborated not only to establish design standards for safer vehicles but also to create safer transportation infrastructure to address the incidence and gravity of injury on roadways [30,31,32,33], another leading cause of injury and death in the United States and the world [13,15,27,28].
Governmental organizations and designers have employed principles in their land-use and zoning practices, which improve visibility and surveillance, pedestrian traffic, and visual and emotional stimulation, all of which aim to create environments which deter crime and, in turn, aim to improve inhabitants’ perceived safety, happiness, and mental health [34,35,36,37,38].
With considerations of safe and easy access to healthy foods, entertainment, and pro-social environments, the current literature continues to provide more evidence that the physical, mental, economic, and social health of cities can be improved with deliberate design made to prioritize the manifold aspects of wellbeing.