Cold air inflames lungs and inhibits circulation, increasing the risk of respiratory conditions, such as asthma attacks or symptoms, worsening of chronic obstructive pulmonary disease (COPD), and infection. Cold also induces vasoconstriction, which causes stress to the circulatory system (198) that can lead to cardiovascular effects, including ischaemic heart disease (IHD), coronary heart disease, strokes, subarachnoid haemorrhage and death (198–206). Most of the evidence for the impact of cold on health comes from studies connecting outdoor temperatures to health outcomes. For example, cold spells are associated with increased mortality and respiratory and cardiovascular morbidity (207), and mortality and morbidity rates in countries with cold and temperate climates are higher in winter than in summer (208).
Evidence that cold indoor temperatures have adverse consequences for health is growing (209, 210). Cold indoor temperatures are often a consequence of outdoor temperature, structural deficiencies, including a lack of insulation and airtightness, and lack of heating. As outlined in this chapter, cold indoor temperatures have been associated with increased blood pressure, asthma symptoms and poor mental health. Cold homes contribute to excess winter mortality and morbidity. Most of the health burden can be attributed to both respiratory and cardiovascular disease, especially for older people. In children, the excess winter health burden is mostly due to respiratory disease. Excess winter deaths due to cold housing has been estimated at 38 200 per year (12.8/100 000) in 11 selected European countries (18).
Winter mortality is greater in countries with milder climates than in those with more severe winter conditions (211), in part because countries with mild winters often have homes characterized by poor domestic thermal efficiency that are harder to heat than well insulated houses in more extreme climates. In insulated dwellings, thermal insulation reduces conductive heat loss through the buildings’ walls, ceilings and floors. Retrofitted insulation, otherwise known as “weatherization” also reduces convective heat loss by blocking unwanted air leaks through the building envelope. As outlined in this chapter, retrofitted insulation, weatherization, and heating can help mitigate the effect of otherwise cold housing on health.
Socioeconomic factors play an important role in determining whether a dwelling is sufficiently warm. Income constraints force people to live in housing that is older, more likely to be poorly built and lacking insulation. These deficiencies, in addition to lack of energy affordability, can make it especially difficult for people on low incomes to heat their houses adequately. For example, a study carried out in South Africa showed that informal dwellings were more vulnerable than other types of dwellings to indoor temperature instability, which affected thermal comfort (212).
In order to assess the evidence on minimizing the health risks associated with cold indoor temperatures and the effects of insulating houses, two systematic reviews were commissioned.
Question for the first systematic review (exposure)
Do residents living in housing where indoor temperatures are below 18 °C have worse health outcomes than those living in housing with indoor temperatures above 18 °C? The categorical cut-off point at 18 °C was chosen based on the conclusions of a previous WHO working group on indoor environment finding that “there is no demonstrable risk to human health of healthy sedentary people living in air temperature of between 18 and 24 °C” (213).
The systematic review focused on the following priority health outcomes, as ranked by the GDG:
respiratory morbidity and mortality
all cause-mortality in infants
hospital admissions
cardiovascular morbidity and mortality
depression.
Question for the second systematic review (intervention)
Do people living in housing with insulation have better health outcomes than those living in housing without insulation?
The systematic review focused on the following priority health outcomes, as ranked by the GDG:
4.1. Guideline recommendations
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| Recommendation | Strength of recommendation |
|---|
 | Indoor housing temperatures should be high enough to protect residents from the harmful health effects of cold. For countries with temperate or colder climates, 18 °C has been proposed as a safe and well-balanced indoor temperature to protect the health of general populations during cold seasons. | Strong |
| In climate zones with a cold season, efficient and safe thermal insulation should be installed in new housing and retrofitted in old housing. | Conditional |
Remarks
There is an association between cold indoor temperatures and adverse health effects, and an association between retrofitting insulation in housing and improved health outcomes. Implementing agencies should work to increase temperatures in cold homes, including through installing insulation with appropriate ventilation, as this is likely to have beneficial effects on health.
While current evidence is insufficient to establish the precise temperature below which adverse health effects are likely to occur, there is high certainty that taking measures to warm cold houses will have significant health benefits and a minimum of 18 °C is widely accepted.
A higher minimum indoor temperature than 18 °C may be necessary for vulnerable groups including older people, children and those with chronic illnesses, particularly cardiorespiratory disease (
213).
The GDG assessed the certainty of the evidence to indicate the extent to which the research supports the recommendation. The certainty of the evidence that warming a cold house reduces the risk of cardiovascular disease is moderate (based on the findings for blood pressure). The certainty of the evidence that installing insulation is associated with improved health outcomes is high but this is qualified by different types of insulation.
Having considered the certainty of the evidence, the values and preferences associated with indoor thermal condition, the balance of benefits to harm related to increasing indoor temperatures and installing insulation, and the feasibility of taking these measures, the GDG made a strong recommendation regarding cold and a conditional recommendation regarding insulation.
4.2. Summary of evidence
This section summarizes the systematic reviews of the associations between indoor cold and health outcomes, and the benefits to health of thermal insulation in the home environment. The systematic reviews on indoor cold and on insulation against cold and the GRADE tables used to assess the certainty of the evidence are available online at http://www.who.int/sustainable-development/publications/housing-health-guidelines/en/index.html in Web Annex B and Web Annex C.
4.2.1. Respiratory morbidity and mortality
Of the four studies identified in the systematic review, three found that colder indoor temperatures increased respiratory morbidity. One cross-sectional study in adults with COPD found better health status with more hours of indoor temperature at and above 21 °C. A dose-response trend was observed for number of days with bedroom temperatures of 18 °C and above for at least 9 hours. The greatest effects were observed in adults who smoked compared with non-smokers (214). Similarly, modelling based on the results of a randomized trial involving children with asthma found that every 1 °C increase in room temperature below the threshold of 9 °C, was associated with a small but significant increase in lung function. Bedroom exposure was shown to have stronger association with asthmatic children’s lung function than living room exposure (215). In addition, one cohort study, including adults with COPD, from China reported reduced respiratory problems with an indoor temperature at 18.2 °C regardless of whether indoor humidity was low, moderate or high (216). In contrast, a case-control study in children with and without upper respiratory tract infections showed no consistent associations with indoor temperature (217).
The certainty of the evidence that warming a cold house (perhaps to a minimum indoor temperature of 18 °C) would reduce the risk of respiratory mortality and morbidity was assessed as moderate.
4.2.2. Cardiovascular morbidity and mortality: blood pressure
Of the six included studies that assessed the association between indoor temperature and blood pressure, all showed that lower temperatures were associated with higher blood pressure, including two randomized trials in Japan that found higher blood pressure in people living in colder homes (218, 219).
A cohort study in Japan of adults over 60 years of age found that decreases of 1 °C in indoor temperatures were significantly associated with increased blood pressure levels at different times of the day, even after controlling for potential confounders (220, 221). There was a stronger association of indoor temperature than outdoor temperature with ambulatory blood pressure, which suggested that excess winter cardiovascular mortality could be prevented by improving the housing thermal environment (221). Two cohort studies from Scotland found people in housing heated to less than 18 °C had a greater risk of high blood pressure (222, 223). This risk increased if temperatures were below 16 °C (OR 4.92) (223). Similarly, a cohort study in the United Kingdom found a decrease in systolic and diastolic blood pressure of 0.5 mmHg per 1 °C increase in room temperature (224).
The review also identified five studies of temperature and blood pressure that were done under laboratory conditions (225–229). The studies show a relationship between warming and lower blood pressure but, because this is indirect evidence for the relationship between blood pressure and housing indoor temperature, the studies were not used in formulating the recommendations.
The certainty of the evidence that warming a cold house (to a minimum indoor temperature of 18 °C) would reduce the risk of cardiovascular mortality and morbidity was assessed as moderate.
4.2.3. Insulation and weatherization
Of the 11 studies identified in the systematic review, seven found some association between the benefits of living in an insulated home and improved health. For example, a cluster randomized trial in New Zealand on the effect of insulating existing homes where at least one person in the household had existing chronic respiratory symptoms found that insulation was associated with reduced odds of poor mental health, self-reported wheezing in the previous 3 months, winter colds or flu, and morning phlegm in adults (39).
While mental health was improved in one controlled trial from the United States of America, the study did not find any differences in general health status between people receiving new insulation and exterior cladding and those in the control group (230). One quasi-experimental study from the United Kingdom found no difference between asthmatic and healthy children with regard to different glazing systems (231). Another quasi-experimental study in New Zealand found that all-cause mortality was significantly lower in people with a history of cardiovascular disease if they lived in an insulated rather than an uninsulated house and non-significantly lower in people with a history of respiratory disease (232). Similarly, a controlled trial from the United Kingdom did not detect any effect of external insulation on general respiratory symptoms, asthma, physical or mental health or subjective well-being (233).
A cross-sectional study from the United Kingdom investigated the effects of different types of insulation on a range of health outcomes (234). The study identified positive effects of loft and external wall insulation on respiratory, mental and general health; but found a negative impact on these outcomes with cavity wall insulation.
Three retrospective cohort studies investigated the effects of living in an insulated home on health. A New Zealand study of 45 000 households, with matched controls, showed no relationship between living in an insulated home and rates of hospitalization. However, mortality rates for adults aged 65 and over who had previously been hospitalized for circulatory illness were lower for people living in insulated dwellings (235). A study from Scotland, looking at the indoor environment and health outcomes as reported by participants, found that rates of coughing were significantly lower in homes with double-glazed windows but no consistent relationship between wheezing and coughing, and insulation (236). A study from Greenland, of households with children aged 3 to 5 and 8 years who had a previous medical attendance for acute otitis media, found no relationship between episodes of acute otitis media and self-reported poor insulation, defined as “reports of draft along the floors and through doors and windows” (237). A historical cohort study conducted in the United Kingdom reported that double glazing improved the household health status by 4.8% but did not detect effects on quality of life or other measures of well-being (238).
One case-control study from Denmark, which had a high risk of bias, found that eye irritation and throat dryness (connected to respiratory health) decreased slightly when windows were replaced, but the results were not statistically significant (239).
The certainty of the evidence that living in insulated homes is associated with improved health outcomes was assessed as moderate.
4.3. Considerations for implementation of the guideline recommendations
In a cold climate, a healthy indoor thermal environment can be achieved through a combination of thermal insulation and heat supply. Building a properly ventilated and thermally insulated house is more technically advanced and expensive than building a non-insulated house, but is likely to lead to health and other benefits, with some evidence that the cost–benefit ratio can be as high as six (232). On a macro-level, improving energy efficiency of dwellings was found to lead to cost savings and in some countries the clear co-benefits of retrofitted insulation on health and energy efficiency mean that these retrofits are already subsidized by governments. For example, it is estimated that improvements in occupants’ health by improving housing in the United Kingdom, including through increasing warmth in bedrooms, would save the United Kingdom health services £1.4 billion in the first year in treatment costs alone (240). An insulation subsidy programme in New Zealand found reduced hospitalization costs due to fewer re-admissions, fewer transfers and shorter stays in hospital, although the rate of hospitalization was unchanged (40). In Cape Town, retrofitting of 2300 houses with solar water heating and roof insulation as part of the Kuyasa low-income housing project had multiple benefits for climate mitigation, respiratory health, poverty reduction, and economic development (241). Besides generating 2.82 tonnes of carbon credit per house annually and lowering heating expenditures, the improved insulation led to a “substantial decline in bronchial and related illness among residents, especially during winter” (241). More broadly, energy efficiency measures contribute to public savings by reducing the burden on energy infrastructure and the climate. Insulation can also help moderate extreme heat situations, as discussed in Chapter 5. Yet, cost–effectiveness will vary significantly for different climate zones and depends on housing quality, the type of insulation, the prior level of insulation and means of heating and ventilation of the housing stock.
At an individual level, there is a clear trade-off between investment costs (installing or retrofitting insulation and heating) and running costs (paying for energy). While people with low incomes are likely to benefit the most from public thermal efficiency programmes because they are more likely to live in cold homes (52), they will also be less likely to be able to afford to install insulation if the costs need to be covered by the inhabitants or home owners. Therefore, it is essential to ensure that low-income people can afford to live in improved buildings, potentially through providing public support for housing costs; otherwise improvements in insulation might increase inequities (242).
Key instruments for policy-makers to improve thermal conditions at national level are: improving building standards and mandating insulation and efficient heating in housing, including the installation of solar panels, implementing subsidies and tax incentives to encourage the installation of insulation and efficient heating; measures to encourage energy affordability through subsidizing or replacing traditional energy costs; and the building of replacement housing where housing is in such disrepair that it cannot be renovated to a standard that ensures adequate temperatures.
To avoid unintended harms of installing insulation, care must be taken to ensure that measures to improve the warmth of dwellings also provide adequate ventilation. Ventilation standards for housing are available from several organizations, such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 62 (243) and in Europe, the standards of the Buildings Performance Institute Europe (244). Weatherization reduces heat loss via air leaks through walls and ceilings, but it can also reduce the necessary air exchange of the building. Household activities, including cooking and washing, as well as human metabolism, generate water vapour. Without adequate ventilation, either natural or mechanical, dampness accumulates inside the building. Insufficient airflow increases indoor humidity, leading to an increase in dampness and growth of mould and bacteria (245). Dampness or mould is associated with a range of adverse health effects, including asthma, respiratory infections and symptoms, dyspnoea, hypersensitivity pneumonitis and allergic alveolitis (246). Guidance regarding indoor air quality, including in relation to mould, is available from WHO and summarized in section 8.2.
It is critical that any intervention to increase the indoor temperature is achieved through sustainable and energy effective solutions. Installing insulation and efficient heating can contribute to the reduction of carbon emissions by enabling people to heat their homes more efficiently. This reduces air pollution and indirectly benefits health through reducing mortality and morbidity associated with outdoor air pollution. These measures also reduce the burden on energy infrastructure and support climate change mitigation (39).
Implementation also needs to consider the importance of using safe insulation materials, which are free of toxic substances such as asbestos and isocyanate, and are resistant to fire and microbial growth. Improved occupational safety and health protection and training for those involved in installing and maintaining thermal insulation may also be required to ensure that the health of workers is not compromised and that the intervention will be optimally effective (247). Authorization of the building retrofit designers and approval/ inspection of the actual work are necessary to ensure healthy and energy efficient results.
4.4. Research recommendations
The specific mechanisms underlying the association between cold homes, lack of insulation, and poor health may involve both physiological responses or co-exposures to other associated factors causing adverse health problems, such as damp, mould, poor quality housing, poverty and social deprivation. Further research is needed to investigate these associations and underpin the research priorities summarized in and for the exposure (cold) and for the intervention (insulation).
Research recommendations: cold.
Research recommendations: insulation.
