Last year, that ratio stood at almost 1:1.

Higher density has arrived. This raises interesting questions about the impact of density on public health.

On the positive side, a common argument in support of greater density from a health perspective revolves around its ability to house more people within closer proximity to transport, employment and community facilities and thus to encourage more active forms of transport such as cycling, walking and use of public transport. This contrasts to the sedentary lifestyle which is facilitated within lower density and vehicle dependent environments.

Density may have other health benefits as well. By reducing commuting times (and thus increasing times for activities such as cooking) and by placing people closer to a greater variety of fresh food options, density may facilitate healthier eating habits and less consumption of processed and/or takeaway food. Denser environments also facilitate the provision of healthcare to greater numbers of people and place more people within greater proximity of facilities such as parks, swimming pools and gymnasiums - the latter two sometimes being featured within apartment complexes.

On the flip side, however, density can also lead to a loss of backyard space and quiet streets which provide safe environments in which children can engage in outdoor activities along with a loss of opportunities for adults in terms of activities such as gardening. By putting more people on or near main roads, it could also expose people to localised pollution and pedestrian traffic hazards.

In terms of mental health, density could facilitate more exercise and greater social interaction if done well but could deliver stressful and noisy environments as well as social isolation if done badly.

A lot of research looking into the phenomenon has been done by the Heart Foundation. In 2014, its Victorian division conducted an evidence review into the relationship between urban density and public health specifically in terms of cardiovascular health.

The outcome was mixed. On the positive side, the researchers concluded that there was considerable evidence that those living in higher densities undertook greater levels of walking and physical activity, that lower densities delivered a higher likelihood of being overweight or obese and that there was emerging evidence of linkages between low residential development and coronary heart disease - albeit with such evidence remaining in its infancy. Nevertheless, the foundation found that there was limited evidence examining the direct relationship between residential density and cardiovascular outcomes and firm conclusions were not able to be drawn as to any relationship between residential density and the physical activity behaviours of children or adolescents.

There was also insufficient evidence to draw conclusions about ideas that low density development results in more time in sedentary leisure-time pursuits.

An earlier and broader review which the foundation commissioned was prepared by the University of Western Australia in 2012.

On the positive side, that review found that:

  • A strong body of evidence confirms that higher residential densities are linked to increased transport walking across all age groups
  • Amongst all age groups, living closer to transport and shops was astrong predictor of walking, both for transport and recreational uses
  • Although there was some evidence of a positive relationship between crowding and mortality rates and some evidence of a positive association between density and overall mortality rates within some age groups, there was little clear evidence linking increases in population density with mortality rates overall
  • Higher residential densities appear to be protective ofcardiovascular mortality through higher levels of physical activity associated with transport walking and decreased sedentary behaviour leading to lower levels of obesity and blood pressure, although the evidence is inconclusive because of difficulty in separating the impact of density from socio-economic factors

On the negative side, however, the review also found that:

  • A small number of studies had found positive relationships between density and overall cancer mortality and breast cancer mortality in women, although this was inconclusive as studies had generally not adequately adjusted for socio-economic factors
  • Studies had consistently shown a link between higher densities and higher road traffic mortality, although evidence in this area was again inconclusive as few of the reviewed studies focused specifically on intra-urban difference or accounted for the fact that residents in lower density cities tend to drive further and more often compared with their high-density counterparts
  • There is consistent evidence that proximity to busy roads, high traffic density and greater exposure to pollution were linked to a range ofrespiratory conditions across all age groups
  • Whilst greater walking associated with density was a positive, living in an environment of ongoing noise, pollutants or overcrowding can result in chronic stress, which has adverse implications in terms of mental health.

In terms of density promoting better health overall, Professor Susan Thompson, a planning expert who heads the City Wellbeing Program at the University of New South Wales, says this depends upon how well it is done.

In order to support more active lifestyles, Thompson says density must be accompanied by features which make walking more attractive. These include street patterns which promote connectivity, streets within which people feel safe and nearby destinations such as shops and community facilities which people want to access.

Second, Thompson says density must be done on a "human scale", in which cities are designed for people, buildings of excessive height are avoided and an ample supply of open space is provided. Buildings of reasonable heights (typically no more than seven or eight storeys), she says, are more human scale and may restrict the degree of physical and mental stress associated with governance issues and the sharing of spaces.

Adequate provision of nearby green space and parks in which children can be active, meanwhile, can help to offset the loss, especially to children, of backyard space and quiet street space.

Finally, Thompson said good acoustic construction is needed to minimise noise impacts.

"It's a complex situation," Thompson said, asked whether density was beneficial or otherwise for public health. "There is no black and white yes or no."

Peter Sainsbury, a former chief executive officer of the Public Health Association of Australia and an Adjunct Professor with the Faculty of the Built Environment at the University of NSW, expressed broadly similar sentiments.

At its core, Sainsbury says humanity has been trending toward greater density for 12,000 years as people moved out of family groups and accumulated into community groups - whether these be villages, cities or megacities. That, he says, indicates that people naturally want to live together and desire access to the type of benefits which living together brings.

As with Thompson, however, Sainsbury says important elements are required if density is to be done well.

First, greater density must be accompanied by green space and social infrastructure. As an example of where this could have been done better, Sainsbury points to Sydney's Green Square where around 61,000 new people are expected to live in 30,500 new dwellings by 2030. With little in the way of provision for schools, he says many parents will have to drive their children to school each day.

Second, building design is critical. Many developers, Sainsbury says, are thinking carefully about communal space on the ground floor and on individual floors. This can include spaces such swimming pools, gymnasiums, rooftop gardens and spaces where people are able to linger and socialise - the latter of which he says is good for mental health.

The location of buildings is also critical. Whilst development within proximity to transport connections is ideal, Sainsbury says situating them one or two blocks back from main roads helps to reduce exposure to pollution, noise and (especially in the case of children) traffic hazards.

Once developed, apartment complexes need to be maintained - potentially through concierge services which can monitor who enters and leaves the building as well as through adequate servicing, Sainsbury says. Finally, it is critical to ensure that buildings are designed in such a way which minimises greenhouse gas emissions.

As Australia pursues greater density, impacts upon public health will arise.

Whether or not this will be beneficial will depend upon how well these environments, designed and built and maintained.

Andrew Heaton
Industry Journalist