How did your research into housing and health originate?
I have been working on this topic for 13 years. Our research programme centres around generating research evidence which can be used in public policy to promote health. This is a broad topic and investigates the potential for investment in socio-economic determinants of health, like housing, transport, welfare, employment etc, to have an impact on health.
Housing is an area of major public investment and a key policy priority. In addition, the longstanding links between poor housing and poor health suggest investment to improve housing may lead to improved health among the worst off, and may reduce health inequalities. In discussion with our funders, the Scottish Government, housing investment was identified as a priority area to investigate.
What was previously known about the relationship between housing and health?
Although there is a well established link between poor housing and poor health this is complicated by the fact that those living in poor housing are also often on low incomes and experience other deprivations which might affect health. This makes it difficult to disentangle the reasons why or how poor housing affects health, and the extent to which poor housing affects health.
Although there are known hazards, such as lead, radon, and asbestos, it would seem that aside from exposure to these known hazards, living in poor housing can be detrimental to health. We have previously reviewed evidence on the health impacts of poor housing but found few well conducted studies, and our reviews were limited in what they could conclude.
How can the effects of poor housing be separated from the effects of other socioeconomic factors that influence health, such as poverty?
This is the trickiest problem for housing research (and other research which tries to isolate the effects of specific socio-economic determinants of health). Ideally you would want to identify a group which are similar in everything which might affect health except eligibility to move into new housing (or for cross-sectional associations the quality of housing in which they live).
This would mean identifying a group which are similar in age, ethnicity, gender, income, employment status, health status, family structure, marital status, length of time spent living in the same house and neighbourhood etc.
What normally happens is that key variables known to be important determinants for health are controlled for, either by study design or statistically. Ideally, the key variables to control for in studies of housing improvement are housing quality and type at baseline, health status, age, gender, socio-economic status, and eligibility for housing improvement.
The best way to control for these factors, as well as other unknown factors is to use a randomised controlled study design, where the individuals within the target population are randomly assigned to receive or not to receive the housing improvement. At the end of the study, the control group will also receive the housing improvement.
What ethical issues do studies like this raise?
Randomisation is justified on the grounds that the benefits of an intervention are uncertain. Although it may be the case that the health benefits of housing improvements are uncertain, the other benefits such as improved warmth, reduced fuel bills, increased space, improved aesthetics, may be viewed as tangible to residents.
Housing improvements will often take some time to roll out across a population, and it can be possible to randomise people to a waiting list which will be in place anyway to allow the improvements to be delivered in phases.
Although some randomised trials of housing improvements have been conducted these require high levels of co-operation and consent with housing providers and tenants. Most often the health impacts of housing improvements have been evaluated using a quasi-experimental design, where the control group do not receive the intervention.
What did your review involve?
We conducted a systematic review of the health impacts of housing improvement. We included studies from any timepoint or language, any study design, and which assessed any health outcome following housing improvement.
We focussed on general housing improvements and did not include interventions aimed at reducing exposure to known hazards such as lead, asbestos or radon.
What did your review find?
We found 39 studies which assessed changes in health following housing improvement. The studies covered a wide range of housing improvements.
The housing improvements in high income countries, and conducted in the past 30 years, included refurbishment, rehousing, relocation, installation of central heating and insulation. Studies from the developing world included provision of latrines. Older studies (pre-1965) examined changes in health following rehousing from slums.
Overall, it would appear that improvements to housing conditions can lead to improvements in health. Improved health is most likely when the housing improvements are targeted at those with poor health and inadequate housing conditions, in particular inadequate warmth. Improvements in warmth and affordable warmth may be an important reason for improved health. Improved health may also lead to reduced absences from school or work.
Why do you think improvements in space and warmth were important to achieving better health for people with respiratory disease?
Although the biological mechanisms may not be exactly understood, people with existing respiratory disease are particularly susceptible to the effects of living in a cold and damp house.
Data from the qualitative studies which asked people about how the housing improvements affected their lives and their health were included in this review. These data suggest that provision of affordable warmth allowed people to heat more rooms and so increase the amount of usable space in the house without an increase in fuel bills.
The increase in usable space was also reported to lead to improved relationships within the household, improved levels of privacy, and increased opportunities for leisure and studying in the house. It is possible that these changes might lead to long term improvements in socio-economic determinants of health, and ultimately long term health improvement.
Where fuel bills were reduced this will lead to an increase in disposable income for spending on essential items such as food. While energy efficiency measures can lead to reductions in fuel bills, this will depend on levels of fuel use, and changes in the unit cost of fuel.
Why are people more likely to get ill if they live in cold temperatures?
Cold temperatures are a source of stress to the body and initiate physiological responses. Vulnerable groups, such as the elderly, young children, and those with impaired cardiac or respiratory function are particularly susceptible to hypothermia, if they do not move around much, but are also particularly susceptible to illness as a result of cold temperatures.
Why do you think housing improvements resulted in greater health benefits when they were targeted at those living in the poorest housing and were less clear in housing improvement programmes delivered across whole neighbourhoods?
The most likely explanation for this is that the potential for improvement is greatest among those with poor health. Where an intervention is delivered across a whole area, regardless of individual health status, the population will include a mix of people with poor and good health.
It is possible, even quite likely, that those with the poorest health will have benefited most with respect to health improvement following the housing improvement, but that these changes may not be evident within the reported means of a study population.
Other reasons why programmes of housing led neighbourhood renewal may not lead to immediate tangible health improvements are that these interventions may involve more disruption, even relocation, compared to installation or upgrading of a central heating system.
Also, the extent of and potential for improvement in housing conditions across the area may vary more across the area, as programmes of neighbourhood renewal typically incorporate additional interventions to promote training, employment, etc.
What impact do you think your review will have?
We hope that the findings of our review can be used to inform development of healthy housing investment. But it should be remembered that there are other justifications to improve housing beyond health.
Issues of social justice and energy efficiency are important reasons to improve housing even if it is unclear that the housing improvements will lead to tangible and immediate health improvements.
What plans do you have for further research in this field?
We hope to prepare shorter and more accessible summaries of this evidence synthesis which can be disseminated to evidence users, and audiences beyond public health.
The review that we have just completed has become large due to the growing body of evidence. This is good news, but it may mean that future reviews of housing improvement could benefit from limiting the type of housing improvements included.
For example, it may be appropriate for studies of provision of basic housing amenities in low and middle income countries to be reviewed separately, or for warmth and energy efficiency studies to be reviewed separately.
Where can readers find more information?
Thomson H, Thomas S, Sellstrom E, Petticrew M. Housing improvements for health and associated socio-economic outcomes. Cochrane Database of Systematic Reviews 2013, Issue 2. Art. No.: CD008657. DOI: 10.1002/14651858.CD008657.pub2.
About Hilary Thomson
Hilary Thomson is a Senior Investigator Scientist with the UK Medical Research Council. She works at the MRC/CSO Social & Public Health Sciences Unit, in Glasgow, and is funded by the Scottish Government.
Hilary investigates the potential for public policy investments to contribute to population health improvement, her work involves generating evidence through primary evaluation studies, and systematic reviews. Hilary is an editor with the Cochrane Public Health Review Group.
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