Urban life can present many challenges for public health

People have long migrated to cities in search of  opportunities to improve their lives but rising urbanization is putting  many cities under pressure to ensure that people's needs are met and  their well-being protected.

Urban life can present many  challenges for public health. Cities that do not have effective systems  for clean water, sanitation and waste management, can see spikes in infectious disease such as cholera and diarrhoea.

Cities also face a high burden of noncommunicable diseases linked to social, environmental and behavioural risk factors associated with urban living,  such as air pollution, poor diet and a lack of physical activity. Road  safety and violence are constant concerns, as are mental health issues.

Health is affected by many interconnected factors that go well beyond access to health services. These include infrastructure issues such as housing, sanitation, transport, energy systems and the availability of  green spaces and parks. They also include access to employment, education, and nutritious food.

With more than half of the world's population now living in cities, overcrowding can be a big issue in cities.

Population growth means that by 2050, another 2.5 billion people will be living in cities. This is an opportunity to create cities that protect and promote health through their design, policies and  programmes.

It is not just important for cities themselves: cities are key partners in national governmental initiatives to improve  people's health and well-being. As the implementation sites for national  policies, their success will directly affect the achievement of  national and global goals for development.

The World Health  Organization (WHO) has been working to improve health in cities for  decades and has several key initiatives. As well as the WHO Healthy Cities Network, which takes a holistic approach to urban health, many  different networks and initiatives support cities to work on specific  topics. These include the Partnership for Healthy Cities, which focuses on preventing noncommunicable diseases and injuries, the WHO Global  Network for Age-friendly Cities and Communities, and the Urban Health  Initiative, which focuses on climate and air quality.

Age-friendly cities are key to enabling people to live longer and  healthier lives while fostering more productive societies. Age-friendly cities anticipate and respond flexibly to changing needs in older age  for accessible housing, urban spaces, public transport, health and social support.

The world is rapidly ageing and the number  of older people (aged 60 or over) is growing faster than all other age  groups. Numbers of older people is expected to rise from 962 million to  more than double (2.1 billion) by 2050 and to more than triple (3.1  billion) by 2100.

Most of today's adults and children will  be ageing in cities. Adapting city structures to the    needs of a  growing older population is preparation to meet the challenges of  demographic change.

Ageing can come with many opportunities  such as time to explore new interests, travel, and spend time with  friends and family. However, older people can face specific age-related  issues, including difficulties in moving around, hearing, seeing and  remembering, challenges with current housing, and isolation as social  networks become fragmented (such as if their partner dies or children move away).

When not adapted to the needs of all ages, cities can be difficult environments in which to grow older. To allow  older people to make their way to a health centre, the supermarket or  just to participate in community life, each sector within a city  (housing, urban planning, transport) needs to be working and integrated.  One break in the chain, e.g. inaccessible housing, an unsafe road, poor public transportation, can make it difficult for older people to get  out and about, and may restrict them to their house The WHO  Healthy Cities Network aims to place health high on the agendas of policymakers and to promote comprehensive local strategies to protect  health and encourage sustainable development.

The WHO Global  Network for Age-friendly Cities and Communities is composed of nearly  800 cities and communities in 40 countries, and was established to foster the exchange of experience and mutual learning between cities and  communities worldwide, so that they meet the needs of their older residents.

Creating age-friendly environments requires actions in many urban sectors, as well as combating ageism, enabling  autonomy and supporting healthy ageing in all policies.

WHO's Urban Health Initiative focuses on air quality, emissions and climate, and aims to support cities to have the data, tools, capacity and  processes to factor health into their development policies.