Evidence supporting the health benefits of Housing Diversity
Authors: Alex Kleeman, Dr Lucy Gunn, Professor Billie Giles-Corti.
In local planning, housing diversity is linked to residential density. Research in the physical activity and health literature has focused on the benefits of residential density, which is one important way of providing housing diversity. Research has concentrated on the associations between density and physical activity, cardiovascular health, traffic safety, air quality, safety and security, access to public open space, and sense of place.
Scope of evidence
This section draws on evidence that is predominantly from urban and suburban areas of the UK, USA and Australia. Research suggests that a range of factors influence density, physical activity and other health benefits.
In this section, you will learn more about:
- Density and physical activity
- Density and other health benefits
- Density and cardiovascular health
- Density and traffic safety
- Density and air quality
- Density and location
- Density and public open space
- Density and sense of place
Density and physical activity
Higher population and residential densities are critical in creating mixed-use neighbourhoods, because they provide the customers needed to support local businesses. Higher densities also generally result in more compact land use, thus decreasing the distances between homes and destinations.
The viability of public transport also increases with greater population densities, with studies showing that the prevalence of using public transport (either for work or general purposes) is associated with higher residential density [22–24] and a greater availability of walkable destinations.  Indeed, studies have found that in low-density neighbourhoods with few local destinations, fewer people walk and more people drive. [25, 26]
More recent evidence also points to a link between increased density, decreased automobile use and decreased sitting time, [22, 27–30] with easier access to destinations [22, 29] and better street connectivity [29, 30] also thought to play an important role.
Studies have repeatedly shown that urban sprawl – as characterised by low densities, long and winding street networks, and separated land uses – decreases local walking and increases vehicle miles travelled. [17, 25] In turn, this increases sedentary behaviour. 
There is a strong and consistent connection between higher residential density and mixed-use planning and walking, across all life stages. [4–16] This is particularly evident for walking as a means of transport. Studies have found transport-related walking to be associated with increased residential density, [23, 32–35] land use mix, [32, 35] and access to services and destinations. [34, 35] A recent, large, multi-country study not only confirmed this finding, but also revealed evidence of a potential threshold effect. According to the authors, walking was more likely when population density reached at least 7,500 dwellings/km2, and depending on the type of walking , as much as 12,000 dwellings/km2. 
Given that density was objectively measured and that the thresholds were comparable across a wide range of international study sites, the authors propose that their findings could potentially serve as a meaningful threshold point for future densification plans.
A growing number of studies also support the association between higher residential density and adults’ engagement in active travel (most commonly walking and cycling). [22, 27, 37–40] In some cases, the likelihood of active travel is 2.5 to 3 times higher for adults living in areas with higher residential density. [38, 39]
A similar trend can be observed among children and adolescents, with several studies identifying an association between higher residential density and active travel to and from school. [41–43] Indeed, some evidence suggests that greater density around both the home and the school encourages habitual active transport to and from school.  Other studies have demonstrated a relationship between children’s engagement in moderate to vigorous physical activity (MVPA) and increased residential and intersection density, [45, 46] public transit density,  commercial density, and number of parks. 
One notable exception to this trend, however, was found in a study of Canadian youths, in which urban sprawl (that is, lower density) was positively associated with active transportation and MVPA.  As this finding contradicts the direction of association that has generally been reported for adults and children, it serves to reinforce the complexity of such relationships, and the need to study them across a range of different contexts and population groups.
While not as comprehensive, there is further evidence associating higher residential density and mixed-use development with recreational walking, and with walking generally. [9, 19, 48–51] For recreational walking, residential density and mixed-use development contribute to a varied and interesting environment, which can help entice walkers into the neighbourhood.
However, recreational walking also tends to be associated with other neighbourhood factors, such as the presence nearby of high-quality, well-maintained public open space, and pleasing aesthetics. For example, a large, multi-country study found that greater residential density, land-use mix, street connectivity, proximity to parks, safety from crime, and pleasing neighbourhood aesthetics were all positively associated with adults’ recreational walking. 
The association for density was curvilinear, however, which means the likelihood of recreational walking increased up to a point, but then declined as density increased further. This could mean that in typical urban settings, density encourages recreational walking, but that in extremely dense settings – such as Hong Kong, one of the study sites – greater density may discourage recreational walking, due to increased congestion and a lack of opportunities for physical activity. 
Indeed, another recent study concluded that the social conditions of a neighbourhood are of vital importance, with indicators of physical disorder, which include graffiti and garbage, or a fear of crime having the potential to negate the benefits of increased density and land-use mix. 
Other evidence suggests that greater residential density and mixed land use may help prevent weight gain and obesity.  Indeed, low-residential density is associated with men  and children being overweight,  while decreasing sprawl (indicating denser, more compact communities) has been associated with lower body mass index (BMI) among women.  Growing evidence suggests that suburban sprawl is associated with increased weight,  principally through a reduction in people’s energy expenditure by encouraging car dependence  and more sedentary leisure behaviours. 
A study by Larry Frank and colleagues in the USA found that a person’s likelihood of being obese declined by 12.2 per cent for each quartile increase in mixed land-use and by 4.8 per cent for each additional kilometre walked, but conversely increased by 6 per cent for each hour spent in a car per day.  Physical activity is thought to be a significant way in which residential density influences a person’s weight. That is, denser, well-connected, walkable environments promote physical activity, with the resultant energy expenditure reducing body weight. [56–57]
Once again, the evidence indicates that density is not the only neighbourhood feature linked to weight, with a lack of parks or open spaces,  increased traffic density, poorly maintained pathways, [55–56] poor neighbourhood aesthetics, and increased distance to commercial facilities  also being associated with increased weight or BMI.
The ‘walkability index’ pioneered by Larry Frank and colleagues in the USA in 2009  has been used to measure and quantify the presence of many features of the built environmental, by combining scores for variables that represent connectivity, density and land-use mix. [59–62] Subsequent versions of walkability indices, including those developed in Australia, have modified the land-use mix computation by varying or adding new land-use categories.
Evidence from several countries, including Australia, shows positive associations between neighbourhood walkability and walking for transport across the life course. [10, 19, 63, 64] These indices highlight the combined influences of built environmental features and the importance of a combination of measures for creating active, walkable environments. Population, residential and employment densities underpin the provision, ease of access to, and effects of, diverse land uses and employment opportunities, public transport and destination. If density is too low, it is not possible to have mixed land uses, or nearby and accessible destinations and transit that encourage walking.
Density and other health benefits
A report commissioned by the National Heart Foundation considered the effects of density on a range of health outcomes and for different age groups (children, adolescents, adults and older adults).  The authors concluded that increasing density, if carefully planned, can bring numerous benefits to the environment and to the health of the community, by:
- Increasing the use of active modes of transport and public transport
- Reducing vehicle miles travelled
- Improving air quality
- Reducing traffic congestion
- Providing more affordable housing, and a choice of housing, close to amenities
- Reducing the geographical and carbon footprints of cities.
However, the report suggests that the success or otherwise of implementing policies to increase population density, and to achieve its associated health benefits, depends on three important factors that should be considered alongside the available evidence:
- The building (its location, construction, design, management and maintenance)
- The socioeconomic and cultural make-up of residents and the local neighbourhood
- The quality and amenity of the neighbourhood environment.
The following sections summarise the literature on the effects of density on various aspects of human health, as reviewed in the National Heart Foundation report.  For the full report, see the National Heart Foundation website.
Density and cardiovascular health
Longitudinal data suggests that density may help protect people against cardiovascular disease. One such study found that women living in denser communities were at a lower risk of illness and death related to coronary heart disease.  Increased density appears to protect individuals from cardiovascular disease through its influence on cardiovascular disease risk factors and its associations with participation in physical activity (principally through transport walking), decreased sedentary behaviour, and lower obesity levels. 
Density and traffic safety
The connection between traffic speed and risk of injury to pedestrians and cyclists is undisputed.  As speed increases, both the likelihood and severity of a crash increase. This applies to all road users, but unprotected road users are particularly vulnerable to speed.  Lowering traffic speeds can reduce injury and encourage walking and cycling. 
Studies examining the association between road traffic accident deaths and population density consistently show an inverse relationship.  Higher mortality of motor vehicle occupants (per 100,000 population) is associated with decreasing population density. Death following road traffic injury is more likely as population density decreases.
Similarly, correlations have been found between urban sprawl and pedestrian and vehicle occupant fatalities.  Ewing and colleagues, for example, ranked nearly 450 metropolitan US counties using a sprawl index and found a strong correlation between sprawl and pedestrian and vehicle occupant fatalities.  Traffic fatalities in the most sprawling counties were nearly 10 times higher than in the most compact. 
Another study examining child pedestrian collisions found that higher dwelling density was associated with lower collision rates, and that walking to school was no longer associated with collisions – after controlling for population density and design features.  This – along with the greater body of evidence – suggests that more compact and higher-density cities have fewer pedestrian and vehicle occupant collisions and fatalities, plausibly due to shorter trips and slower traffic speeds than in more sprawling areas with wider roads that allow cars to travel at faster speeds.  However, in higher-density environments with mixed land uses there are likely to be more pedestrians and cyclists, and this could increase the risk of injury. Therefore, in such areas it is important to provide adequate walking and cycling infrastructure and traffic-control measures.
Density and air quality
Proximity to busy roads, high traffic density and increased exposure to pollution are linked to a range of respiratory conditions across all age groups.  Higher-density neighbourhoods have the potential to improve people’s respiratory health by providing the population densities necessary to support good-quality public transport and encourage walking and cycling as viable alternatives to private vehicles. Indeed, some evidence suggests that there is a significant negative association between residential density and vehicle miles travelled,  while others have found land-use diversity, intersection density, and proximity to commercial areas to be more influential. 
The effects of higher-density housing on respiratory health depend also on housing design and location.  Residential developments should be located away from major roads that carry high traffic volumes. They should be in areas with sufficient and regular public transport with infrastructure that supports walking and cycling. Balconies, windows and draw-points for air conditioners should not be oriented towards heavily trafficked or congested roads, or intersections where motor vehicles idle. Designers should also consider the local prevailing winds and topographic characteristics, to avoid building higher-density housing downwind of busy roads.
Residential density may also affect mental health, both directly via environmental stressors such as crowding, noise, indoor air quality and light, and indirectly via other factors influencing activities of daily living and social interactions between residents. It seems that the location, design, construction and quality of housing affect mental health, rather than density per se. 
Noise appears to affect mental health by causing annoyance, which in turn causes stress. However, the amount of noise residents experience relates to the housing’s location (for instance, on a busy road) and quality (such as construction and insulation). For example, one study found that exposure to automobile commuting and the resultant noise was associated with depressive symptoms, but that higher residential density was in fact associated with fewer depressive symptoms (possibly due to greater walkability, leading to greater levels of non-motorised travel). 
Another study found that residential density, along with commercial density and industrial land use, were associated with sleep problems and shorter sleep duration. However, these associations lost all significance after controlling for traffic levels and noise – signifying that it is the noise and traffic associated with such land uses that reduce sleep, rather than the land uses themselves.  Higher housing quality in itself is consistently associated with psychological health. 
Density and location
Within a neighbourhood, the location and density of residential dwellings help determine people’s access to neighbourhood resources. Traditional neighbourhoods tend to contain a diverse mix of destinations, integrated in close proximity to a variety of residential dwelling types. This allows residents to undertake and fulfil a variety of daily activities and needs (live, work, play) in their neighbourhood.
Living near a supermarket, and increased density of supermarkets in the neighbourhood, have also been associated with healthier eating – assessed by eating more fruit and vegetables, a healthier and better-quality diet, [74–77] and lower weight. [78–80]
In contrast, conventional neighbourhoods consist of uniform residential dwellings situated on large lots, with few (if any) walkable destinations nearby. They tend to be served by large, automobile-oriented shopping complexes, such as big-box retail or shopping centres, shopping malls and office parks that are removed and segregated from residential areas. Residents of conventional neighbourhoods have nowhere to walk to; their work, leisure and recreation activities are usually undertaken outside the neighbourhood.
Living near a mix of destinations is associated with higher levels of active transport across all age groups. Living near destinations such as shops and parks is associated with more transportation walking by adults, [17–21] and by older adults.  The presence of local destinations, facilities and services, combined with the attractiveness of the neighbourhood, can make residents feel more satisfied with their home and neighbourhood – this correlates closely with better mental health.
For example, a recent New Zealand study on transit-oriented developments (higher residential density, close proximity to public transport and greater levels of walkability) found that residents expressed greater satisfaction with their housing. The authors concluded that ‘this satisfaction is derived as much from the housing units as it is from the amenities and services of the neighbourhood centre’. [81, p.13]
By contrast, a British study of families with young children found a negative relationship between residential density and neighbourhood satisfaction. However, it was hypothesised that the higher-density areas under examination were less popular largely because they had more crime, noise and traffic, and lacked neighbourhood attractiveness. 
A comprehensive review of the relationship between density and social sustainability also found that residents of high-density environments were more likely to report poorer neighbourhood quality and feeling less safe, than were residents of lower-density neighbourhoods, further emphasising the importance of the location of dwellings and their surrounding amenities. 
Density and public open space
Access to public open space is especially important for people living in higher-density housing, because it substitutes for the private space available to residents of low-density dwellings.  Although few studies have explored density and public open space per se, there is considerable evidence that exposure to public open space, parks and nature improves mental and physical health, and is associated with increased levels of walking across all age groups.
Neighbourhoods with more parks and public open space see higher physical activity levels in children, adolescents, adults and older adults.  There is some evidence that young people and adults who live nearer to large, attractive public open spaces are more physically active. [84–87] Public open space also brings broader community and health benefits, rather than promoting physical activity alone.
Exposure to natural environments appears to restore and benefit mental health;  the presence of attractive public open space is associated with better mental health for adults; and access to nature and green space improves children’s mental health. [89–92] Contact with nature has been associated with a number of health benefits for children, such as improved cognitive function, increased creativity, improved interaction with adults, reduced attention deficit hyperactivity disorder symptoms, and reduced rates of aggression. 
Higher prices paid for dwellings near public open space indicate the value of such space for residents of higher-density housing. Neighbourhood attractiveness, including the amount of green space, is also an important correlate of housing satisfaction (which in turn influences mental health) for apartment dwellers in particular – more than for residents of other types of housing. 
Thus the evidence indicates that providing public open spaces around higher-density development is essential for promoting active living and improving the physical, psychological and social health of individuals and the community. However, more research is needed to determine the exact amount or types of public open space required to meet the needs of different users and population groups in areas of different densities. For more information, see the Public Open Space design feature.
Density and sense of place
Evidence also suggests that walkable (denser, mixed-use and more connected) environments strengthen residents’ sense of community and social capital, by encouraging and facilitating social ties or community connections through opportunities for residents to meet, interact and become more actively involved in their neighbourhood. [94–96]
Moreover, mixed-use planning and the presence of a variety of destinations and housing types and population sub-groups promote walking, which in turn increases the sense of place, community and social capital through greater interaction between residents. 
However, higher-density environments have been linked with lower sense of community, feelings of cohesion or amount of social interaction between residents. [27, 97, 98] This may be due to a higher frequency of – and exposure to – unavoidable contact with unfamiliar people, which could potentially cause residents to withdraw from social settings in order to minimise such contact.  Indeed, an Australia-wide study of older adults found that social cohesion was greater among residents of low-density areas, whereas perceived danger and neighbourhood problems increase with higher density. 
Summary of evidence
|A diversity of housing types helps cater to the housing needs of people at different stages of their lives, and of an increasingly diverse range of household types.|||
|Higher population and residential densities are critical in creating mixed-use neighbourhoods. There is consistent evidence that the combination of higher residential densities and mixed land-use is associated with adults and older adults walking more.||[4–16]|
|Although not as comprehensive, evidence associates higher residential density and mixed-use development with recreational walking and walking generally.||[9, 19, 48–51]|
|Increased density appears to protect individuals from cardiovascular disease, through its effects on cardiovascular disease risk factors, its association with physical activity (principally transport walking), decreased sedentary behaviour, and lower prevalence of obesity.|||
|Although few studies have explored density and public open space per se, there is considerable evidence that easy access to public open space, parks and nature is beneficial to mental and physical health, and is associated with increased levels of walking – by all age groups. Public open space is especially important for people living in higher-density housing, as a substitute for the private space available to residents of low-density dwellings.||[10, 84–92]|
|Evidence also suggests that walkable environments (those that are denser, mixed-use and better connected) increase people’s sense of community and social capital, by encouraging and facilitating social ties or community connections through opportunities for residents to meet and interact and become more involved in their neighbourhood.||[94–96]|
|Greater density, if carefully planned, can bring numerous additional benefits to the environment and health of the community: by reducing vehicle miles travelled; improving air quality; reducing traffic congestion; providing more affordable and diverse housing that is close to amenities; and reducing the geographic and environmental footprint of cities.|||