The relationship between temperature and health

According to the Office for National Statistics (ONS), an estimated 43,500 excess winter deaths [(EWDs) defined as the number of deaths that occurred in the winter period minus the expected number of deaths for that period based on non-winter months] occurred in England and Wales in 2014/15, and these deaths were concentrated among older people.⁴ Not only is this the highest number since 1999, but it is also higher than in countries with colder winters, such as the Scandinavian countries, which suggests that many of these deaths may be preventable. EWDs therefore represent an important public health challenge, and a reduction in EWDs is one of the outcomes outlined in the Public Health Outcome Framework for England 2016–19, as part of the ‘Healthcare public health and preventing premature mortality’ domain.⁵

The association between cold outdoor temperatures and health risk has long been documented in the literature.^6,7 A small body of research in epidemiology^8,9 has also demonstrated that lower indoor temperature may be key for understanding EWDs, which are largely considered to be caused by fuel poverty rather than temperature itself.¹⁰ The World Health Organization (WHO) recommends a minimum temperature of 21 °C in living rooms and 18 °C in all other rooms.¹¹

Cold outdoor temperatures act as an unexpected negative income shock as households need to increase fuel expenditure to keep warm. Fuel-poor households are therefore potentially faced with a ‘heat-or-eat’ trade-off, in which they have to decide whether to increase expenditure on heating and cut back on other consumption or live in cold homes.¹² Older people are particularly vulnerable to such income shocks as they are likely to be on low and/or fixed incomes, spend more time in the home and live in energy-inefficient homes.¹³ Older individuals are also particularly vulnerable to cold-related health impacts. Poor physiological thermoregulation is evident in older people, even in response to mild cold stress. Circulatory (e.g. heart attack, coronary thrombosis), respiratory (e.g. respiratory tract infections) and mental health problems (e.g. depression, anxiety) are considered likely to be associated with low indoor temperatures, via mechanisms involving increased blood pressure and viscosity, inflammation, bronchoconstriction, mucus production and clearance, immune suppression, stress, discomfort and social isolation.¹⁴

The UK government has several long-running policies (e.g. WFP, Cold Weather Payments, Warm Homes Discount Scheme) that aim to counter the adverse effects of cold temperatures, particularly among the socioeconomically disadvantaged and the elderly. In this study, we focus on the WFP, an unconditional cash transfer that was introduced in the UK in 1997 to help older people meet the costs of heating during the colder winter months. This research represents the first examination of the potential effect of the £2–3B per annum WFP government policy on biomarkers and reported health measures.

The rationale for the introduction of the WFP is reproduced here:

Winter fuel payments were introduced as part of the Government’s initiative to tackle fuel poverty among pensioners. Winter fuel payments give older people reassurance that they can afford to heat their homes in winter. They are paid in a lump sum each winter to ensure that money is available when fuel bills arrive. Older people are targeted because they are particularly vulnerable to the effects of cold weather during the winter months and older people are more likely to be on fixed incomes.

Kennedy and Parkin.¹

Contains Parliamentary information licensed under the Open Parliament Licence v3.0. See www.parliament.uk/site-information/copyright-parliament/open-parliament-licence/

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Although the goals of the WFP are clear, it is by no means a given that the payment will be spent as desired by the government. From the perspective of standard economic theory, the WFP is viewed as an increase in income that will be spread evenly across expenditures. A recipient of the WFP is not in any way bound to spend this cash transfer on energy or any other specific goods. Distributing the WFP across expenditures as expected by standard economic theory would lead to approximately a 3% increase in fuel consumption.¹² However, initial evidence¹² suggests that > 40% of the WFP is spent on fuel, suggesting that labelling the payment as ‘winter fuel’ may be effective in increasing energy expenditure. The presence of this labelling effect is crucial to understanding our rationale for anticipating that the WFP may have a beneficial impact on household temperature and health. We therefore provide a brief description of research examining this proposed labelling mechanism.

Behavioural interventions and labelling effects

Manipulating labels can be considered a potential behavioural intervention.^15–19 By labelling an unconditional cash transfer with a particular purpose the government signals the intention that recipients spend the transfer on a particular good suggested by the label. In this way, a label can be considered a ‘nudge’ or a way of ‘influencing choice without limiting the choice set’²⁰ and without changing economic incentives.²¹ Typical examples of labelled cash transfers are child benefits and food stamps – although these transfers can be spent on anything or traded and spent on goods if necessary, their labelling tries to influence their destination. Because these payments are unconditional, they do not require expensive monitoring.

According to standard economic theory, labelling cash transfers should have no effect on how the money is spent as it should be fully fungible with other income sources. The fungibility assumption implies that individuals should treat all the money in their bank account in the same way, independently of its source. In the standard framework, the marginal propensity to consume out of all types of income and wealth should be equal. However, behavioural economists have challenged the fungibility assumption, both theoretically and empirically. According to Thaler,²² individuals have a system of mental accounts in which they group categories of income and expenditure (e.g. food, entertainment, housing). Each of these mental accounts might have a specific budget and the marginal propensity to consume can differ across them. Within this framework, individuals are particularly susceptible to sources of income labelled according to one of their mental accounts. Mental accounting, therefore, suggests that the label attached to cash transfers can affect consumption patterns. The underlying idea is that labelled cash transfers may be considered as entering the correspondingly labelled mental account and are therefore not fully fungible with other income sources.

The empirical evidence on the importance of the labelling of transfers is mixed. Kooreman²³ studies how Dutch households spend the child benefits they receive from the government. He found that child benefits are much more likely to be spent on children’s clothing than other income sources are.²³ In other words, the marginal propensity to purchase children’s clothing out of child benefits is much higher than the marginal propensity to purchase children’s clothing out of other income sources. In contrast to this evidence, Blow et al.²⁴ found that, in the UK, child benefits lead to a significant increase in alcohol consumption and the purchase of adult clothing for both couples and single parents.

Abeler and Marklein²⁵ analyse whether or not individuals treat different income sources as fungible using both a natural field experiment and a controlled laboratory experiment. In both experiments, the authors compare the spending patterns of a group that receives a subsidy in the form of cash with those of a group that receives the subsidy as an in-kind benefit. Their results show that individuals do not act in line with the fungibility assumption and that the effect is caused by cognitive limitations rather than preferences. Beatty and Tuttle²⁶ study the effect of a policy that increased food stamps benefits in the USA on food-at-home expenditure. They find that the policy caused an increase in both food-at-home expenditure and the proportion of total expenditure allocated towards food at home. Benhassine et al.²⁷ use a large randomised experiment in Morocco to estimate the effect of an unconditional cash transfer, labelled as an education support and paid to fathers of poor children in rural communities. They show that these transfers, although not conditional on school attendance, increased school participation substantially and performed as well as more expensive conditional cash transfers.

There is also evidence to suggest that labelling the WFP as ‘winter fuel’ may have a substantial impact on how the cash transfer is spent. We provide a brief background to the WFP and detail evidence for the existence of a labelling effect.

The Winter Fuel Payment

The programme targets older people because they are considered particularly vulnerable to the effects of cold weather during the winter months. To be eligible for the WFP, the oldest member of the household needs to be aged > 60 years before the end of the qualifying week of a given year, which for winter 2015/16 was 21–27 September 2015.¹ Individuals who already receive the State Pension or any other social security benefits (95% of cases) do not need to apply; they receive the payment automatically, together with a notification by post that details the amount and timing of the payment. Individuals who do not get any benefits or a State Pension (5% of cases) need to fill in an application form the first time they become eligible (the payment then becomes automatic in subsequent years). These recipients also get a letter that indicates the level and timing of the payment.

The WFP is paid as a tax-free lump sum between November and December of each year and the rate has increased substantially since its introduction in 1997. The payment was £20 (or £50 for those in receipt of means-tested benefits) when it was first introduced in the 1997/8 winter, it increased to £100 in 1999/2000 and then to £200 in 2000/1. An additional £100 for households with a member aged ≥ 80 years was first introduced in 2003/4. In some years additional payments have also been made alongside the ‘standard’ WFP, sometimes for reasons other than to help with fuel bills. Table 1 summarises entitlements from the year in which the WFP was introduced to 2016. According to the Department for Work and Pensions,¹ there are > 12 million people who benefit from the WFP and the total expenditure has been estimated to be over £2B per year, as reported in Table 2.

TABLE 1

Winter Fuel Payment entitlements by year

TABLE 2

Winter Fuel Payment recipients and expenditure

Although this payment can be spent on any goods and services, labelling the cash transfer as payment for ‘winter fuel’ attempts to ‘nudge’ recipients towards increasing domestic heating, thereby combating fuel poverty, raising indoor temperatures and reducing EWDs. However, both the universal entitlement (contingent only on age) and the fact that it can be spent on anything has been a subject of political and academic debate.

In a report published in December 2009 by the Institute for Public Policy Research, Lawton and Stanley²⁸ indicate that the WFP is not a well-targeted expenditure, with approximately 12% of recipients likely to be in fuel poverty. The authors suggest that the WFP could be construed as a non-means tested method for enhancing pensioner income given that take up is close to universal. If the goal of the WFP is to specifically target the fuel poor then, the authors argue, the expenditure is in need of reform.

In another report on fuel poverty in March 2010,²⁹ the House of Commons Energy and Climate Change Committee concludes that the WFP is an unfocused and poorly targeted means of tackling fuel poverty (contains Parliamentary information licensed under the Open Parliament Licence v3.0. See www.parliament.uk/site-information/copyright-parliament/open-parliament-licence/.):¹

As a means of tackling fuel poverty, the case for Winter Fuel Payments is weak. Its payment is unfocused and not targeted on people in or near fuel poverty. However, as a universal means of supplementing pensioner incomes, which is easily understood and easy to pay, the political case for the retention of Winter Fuel Payments is strong. However, it would be more intellectually honest to rename the benefit; concede that it [is] a general income supplement; and stop accounting for it as a fuel poverty measure.

Because of this criticism, in 2014 the government assessed the feasibility of a voucher scheme to pay WFP directly to energy providers. However, the feasibility study showed that there would be significant additional administrative costs to the energy providers that were likely to translate into an increase in fuel bills for all customers.¹

In the social sciences, few papers have assessed the effectiveness of the WFP in tackling fuel poverty and improving health. Using UK data from the Living Costs and Food Survey (LCF) for the years 2000–8, Beatty et al.¹² study the effect of the WFP on fuel spending. In their analysis, the authors use a RDD approach with a sharp eligibility criterion at age 60 years and a window of 15 years on either side (45–75 years). The authors found that, on average, 47% of the WFP is actually spent on fuel. This result is particularly striking given that, if the WFP were treated as cash, we would expect (based on standard economic theory) households to spend only 3% of it on fuel. The authors attribute this effect to the labelling of the transfer, based on the framework of mental accounting developed by Thaler²² and related studies discussed^23–27 in Behavioural interventions and labelling effects. To reiterate, the underlying idea is that households set mental budgets for classes of expenses and labelled cash transfers are disproportionally assigned to the corresponding labelled class. Using the same methodology as Beatty et al.,¹² Lange et al.³⁰ also found evidence for a labelling effect. However, the authors show that the WFP has a distortionary effect, as its labelling induces households to buy fuel instead of cleaner forms of energy, thus reducing the probability of investing in renewable energy by 1.2 percentage points.

Although there is evidence to suggest that the WFP alters energy expenditure, it remains unknown whether or not this leads to warmer homes or to improved health. Iparraguirre³¹ found a positive correlation between the introduction of the WFP in England and Wales and the recent reduction in EWDs in the UK. However, the study is based on aggregate time-series data (as opposed to individual-based data) without comparison regions, limiting the extent to which changes in mortality can be attributed to the WFP. In the current study, we employ an approach similar to Beatty et al.,¹² capitalising on the sharp eligibility criterion for WFP eligibility to examine the impact of the payment on household temperature and both objectively recorded and self-reported health measures.

Ambient temperature and health

If the WFP is effective in raising home temperatures during cold weather, a key question is whether or not this effect is likely to improve the health of older adults. An initial aim of this study is, therefore, to identify how indoor temperature relates to a set of physiological and self-reported health measures assessed in the English Longitudinal Study of Ageing (ELSA).³² We do this because population-representative evidence documenting the link between ambient indoor temperature and health is largely absent. It is also important to estimate these associations in the UK context given that unique country-specific factors are likely to determine indoor temperature levels and its relation to health (e.g. climate, housing efficiency/insulation level, available income, time spent indoors, body composition, clothing and comfort preferences).

There is a relatively large evidence base suggesting that exposure to cold environmental temperatures is likely to be a primary explanatory factor for increased rates of mortality and morbidity during winter seasons.^6,7 Although excess winter mortality varies between years and regions within individual countries, up to 40,000 deaths, or approximately 60 deaths per 100,000 people, occur annually in Britain as a result of low outdoor temperatures.^33,34 Peak winter mortality can exceed lowest summer rates by as much as 45%,³⁵ with parallel increases in related morbidity largely attributable to ischaemic heart disease and stroke and respiratory disease.³⁶ For example, an analysis covering the years 1949–85 reported that 88% of variation in annual EWDs in England and Wales could be explained by mean temperature, number of influenza deaths and temporal trends.³³

Several lines of evidence suggest that indoor temperature may also be relevant to health outcomes. The cross-national Eurowinter survey³⁷ of seven cities and regions calculated higher percentage increases in mortality per degree fall in winter temperature in areas with warmer, rather than colder, winter climates; greater mortality increases were associated with lower living room temperatures, limited bedroom heating and less frequent use of personal protective measures, such as wearing warm clothing or keeping active when outdoors.³⁸ Indoor warmth, as predicted by household and housing features, was similarly related to deaths per degree fall in outdoor temperature in time-series analyses of English mortality data.⁸ These authors further reported greater seasonal fluctuations in mortality and a 20% difference in EWDs between the coldest 25% of households and the warmest 25%. In an evaluation of the Warm Front Scheme,³⁹ which aimed to increase residential energy efficiency and reduce health effects of fuel poverty in England, households that failed to increase indoor temperatures to WHO-recommended levels post intervention experienced increased mortality with decreases in outdoor temperature (2.2% per 1 °C reduction). In contrast, households that did raise indoor temperatures did not experience an increased risk of mortality.

Cold temperatures probably induce cardiovascular responses via multiple mechanisms involving blood pressure, heart rate variability, haemodynamics, atherosclerotic plaque development and instability, and endothelial dysfunction.⁴⁰ Blood pressure increases and concentrations of inflammatory and coagulation factors that can increase the risk of thrombosis may become elevated.^41–44 For example, C-reactive protein (CRP) and fibrinogen concentrations may also increase in response to respiratory infections,^45,46 which occur more frequently in cold winter weather, possibly because of the confluence of lengthened microbial survival, increased transmission with indoor crowding and individuals’ reduced immune resistance or impaired respiratory function.⁴⁷ Airway infections and resulting inflammation can further reduce lung function by aggravating or triggering acute events in people with chronic respiratory conditions, such as asthma or chronic obstructive pulmonary disease (COPD).^48,49 Inhalation of cold air can act as a direct trigger for bronchoconstriction, especially in such susceptible persons or post-exertionally.^50,51

The remainder of this section summarises epidemiological literature on associations between temperature, cardiovascular and respiratory risk factors and functional measures examined in the current study into health effects of the WFP policy, namely blood pressure, fibrinogen, CRP, lung function and mental health. Research focusing on indoor temperatures is most relevant to this investigation but, as such studies are limited in number, those measuring outdoor temperature are included. Review documents written by the Marmot Review Team¹⁴ and Public Health England⁵² also provide useful background, with overlap to the studies referenced.