Non-optimal temperatures, climate change and cardiovascular disease

Heat, cold, climate and health

Every population has an ‘optimal’ range of temperatures, above or below which its health is adversely affected. Exposure to non-optimal temperatures — both cold and heat — is associated with adverse health effects, including preventable deaths from cardiovascular disease, hospital admissions, and the aggravation of conditions among the chronically ill in Europe (Ryti et al., 2016; WHO, 2021).

Heat and cold have certain things in common in relation to public health:

• The threshold above or below which temperatures become hazardous differs by geographical area, prevailing climatic conditions and population characteristics.
• Their health impacts depend on the timing, intensity and duration of exposure (e.g. a heatwave or a cold wave), and how acclimated and adaptable the local population, infrastructure and institutions are to the prevailing climate.
• Some population subgroups like the elderly, people with disabilities and children are vulnerable to both heat and cold. Several pre-existing illnesses like cardiovascular, respiratory and kidney disease increase vulnerability to both cold and heat.
• The relationship between both hot and cold temperatures and health impacts is heavily influenced by megatrends like population ageing (which makes people more vulnerable to heat and cold), urbanisation (which increases exposure to urban heat islands) and climate change (which increases the frequency and intensity of heatwaves).
• Energy poverty and building quality (e.g. the degree of insulation and energy efficiency), as well as urban design, are also factors that influence the potential health impacts of both heat and cold. They affect the ability to keep dwellings comfortably warm or cool, as well as the ability to protect oneself from hazardous temperatures (Eurostat, 2023; Thomson et al., 2019; UNEP DTU, 2021).

Both heat and cold increase deaths from cardiovascular causes. Very hot days (i.e. with average temperatures above the 97.5^th percentile) and very cold days (temperatures below the 2.5^th percentile) have been estimated to account for 2.2 and 9.1 excess deaths out of every 1,000 cardiovascular deaths, respectively. Heart failure is associated with the highest proportion of excess deaths resulting from extreme hot and cold days, with 2.6 and 12.8 for every 1,000 heart failure deaths, respectively (Alahmad et al., 2023). This pattern roughly applies to the overall health effects of non-optimal temperatures: at a population level, the impacts of cold on health are greater than those of heat. Over 7.6% of cardiovascular deaths in EEA member and cooperating countries^[1] are due to non-optimal temperatures (both heat and cold) (GBD Collaborative Network, 2020). 

Despite some commonalities in public health terms, the way heat and cold affect health and the level of epidemiological knowledge on heat and cold are different, as explained below.

Heat and cardiovascular disease

How heat affects the body, and how that leads to direct and indirect impacts on health and wellbeing, are well-established in science. A rapid heat gain due to exposure to hot temperatures may compromise the body’s ability to regulate temperature, potentially resulting in heat-related illnesses like heat cramps, heat exhaustion, hyperthermia, heatstroke and even death. In addition, heat puts pressure on the respiratory and cardiovascular systems, and worsens pre-existing cardiovascular, respiratory and cerebrovascular diseases, among others. Specifically, heat increases blood flow to the skin, which results in compensatory mechanisms of increased heart rate and pump volume; this also affects blood viscosity and inflammatory responses (Zhang et al., 2022). Most heat-related preventable mortality due to CVD is due to this worsening of pre-existing conditions (WHO, 2021). This worsening can be further exacerbated when there is exposure to heat and air pollution at the same time. Heat and some air pollutants, like PM_2.5 and O₃, have a synergistic negative effect on health (WHO, 2021; SPF, 2023). Moreover, health impacts of heat tend to be aggravated in cities due to the absorption and slow release of heat from buildings and artificial heat-retaining surfaces, the abundance of residual heat sources and the scarcity of green spaces (WHO, 2021).

Exposure to heat in a study covering 16 EU countries was associated with 179,000 preventable deaths from 2000 to 2019, with eastern European and Mediterranean countries having the highest proportion of heat-related preventable mortality, and northern European ones ^[2] the lowest (Zhao et al., 2021; Martínez-Solanas et al., 2021). In 2022, several countries with heat epidemiological surveillance systems reported the deaths attributable to the severe summer heatwaves: around 4,500 deaths in Germany, nearly 4,000 deaths in Spain, around 2,300 in Italy, and more than 1,000 in Portugal (WHO Regional Office for Europe, 2022; SPF, 2023). There is no reason to suppose that other countries for which data are not available would have lower heat-related death rates. Rather the contrary, since all countries mentioned have fully functional heat-health action plans in place that protect the population, at least partially (WHO, 2021; Martinez et al., 2022).

Cold and cardiovascular disease

The links between cold and ill health are complex, involving not only direct impacts like hypothermia but also the aggravation of several types of chronic diseases, and an increase in the transmission rates of various bacterial and viral infections. In direct relation to CVD, cold causes a narrowing of blood vessels, creating more pressure in the circulatory system and forcing the heart to work harder. It can also increase the viscosity of blood, which elevates the risk of clots, stroke or heart attack. These risks are more relevant for those with an existing cardiovascular condition (Manou-Stathopoulou et al., 2015).  

Cold is the second largest environmental risk in terms of burden of disease in Europe, only following ambient air pollution and far above heat; and its health effects are aggravated by energy poverty. Exposure to cold (including cold waves and generally cold temperatures) in Europe (EEA member countries except Turkey) was associated with around 657,000 preventable deaths from 2000 to 2019, with eastern European and Mediterranean countries having the highest proportion of cold-related preventable mortality, and northern Europe the lowest (Zhao et al., 2021; Fowler et al., 2015; Martínez-Solanas et al., 2021). While most cold-related preventable mortality is due to respiratory causes, cardiovascular causes are almost as frequent (Diaz et al., 2005; Linares et al., 2015; Carmona et al., 2016).

Trends in exposure to non-optimal temperatures in Europe

Heat trends in Europe

The world is warming fast, and Europe is warming faster than the global average. The mean annual temperature in Europe in the last decade was around 2°C warmer than during the pre-industrial period. The year 2020 was the second warmest year on record in Europe, and the summer of 2022 the hottest ever recorded. The years 2015-2021 were the warmest years on record in Europe by a clear margin (Copernicus Climate Change Service, 2022). Dangerous heat spells have been increasing in frequency, intensity and duration in the region since 1950 (Donat et al., 2013; ECMWF, 2020). During the same period, Europe’s population has become older and more urbanised; as a result, heat-related vulnerability and exposure in Europe has increased steadily in recent decades. However, there are no consistent reports that heat-related mortality and health impacts have got worse due to this increased vulnerability, attesting to the effectiveness and importance of public health prevention and climate change adaptation (WHO, 2021). On the other hand, projections suggest that temperatures across Europe will continue to increase. In the most optimistic scenario they would still increase by 1.2 to 3.4°C by 2100, while in the most pessimistic one they would increase by 4.1 to 8.5°C (Watts et al., 2020). The projected increase in the intensity, frequency and length of heatwaves will result in a significant rise in the number of people exposed to extreme heat. In a realistic scenario of a global temperature increase of 2°C above pre-industrial levels by the end of the century, the number of people in the EU exposed to what is now a once-in-50-years heatwave would grow to 172 million per year, up from 10 million per year currently (Joint Research Centre (European Commission) et al., 2020). The highest level of warming is projected across north-eastern Europe, northern Scandinavia and inland areas of Mediterranean countries, while the lowest warming is expected in western Europe, especially in Ireland, western France, Benelux countries and Denmark (EEA, 2022c).

Cold trends in Europe

Conversely to heat, studies generally predict that as the climate warms, the effects of cold on health will diminish to some extent. For example, the population annually exposed in Europe to extreme cold is projected to decrease by two thirds by 2100 from around 10 million currently, assuming a 2.0°C average warming. The strongest absolute reductions in exposure to cold extremes are projected for southern and northern European countries. Similarly, the number of deaths related to extreme cold events in Europe is projected to significantly decrease (Joint Research Centre (European Commission) et al., 2020). The decrease in cold-related mortality is, however, not projected to compensate for the increase in heat-related mortality (Martinez et al., 2018; Martínez-Solanas et al., 2021; Staddon et al., 2014). Moreover, there is no current evidence that cold-related mortality has decreased in Europe.

The mortality from current cold exposure warrants urgent action, from policies against energy poverty to cold-health action plans. When it comes to cold and energy poverty, 36 million European residents — 8% of the EU population — said that they were unable to keep their home adequately warm in 2020. The situation varied across the EU with the largest share in Bulgaria (27%), followed by Lithuania (23%), Cyprus (21%), and Portugal and Greece (both with 17%) — see Figure 5 (Eurostat, 2023). The increase in energy prices that started in 2021 and rose further with Russia’s invasion of Ukraine in February 2022 has probably worsened an already difficult situation for many EU residents (European Commission, 2023).

Figure 5. Proportion of people in Europe who report being unable to keep their home warm, by country

Source: (Eurostat, 2023).

Explore different chart formats and data here

Energy poverty tends to disproportionately affect lower income households and those dwelling in low quality housing (López-Bueno et al., 2020; EEA, 2022a). Moreover, indoor and outdoor air quality are severely worsened when solid fuel is used to warm homes, a far more common practice in situations of energy poverty.

What the EU is doing about exposure to nonoptimal temperatures and climate change

The EU has not issued binding regulations or policies to prevent the health impacts of heat or cold. It has, however, implemented several key policies and regulations to address climate change, energy poverty and the built environment.

A detailed account of EU policy on climate change adaptation in relation to health is provided in the European Climate and Health Observatory (EEA, 2022b). The main policy framework which covers climate change mitigation and adaptation is the European Green Deal. This sets out a growth strategy to transform the EU into a fair, prosperous and resource-efficient society with net zero greenhouse gas emissions in Europe by 2050. The 8^th Environmental Action Programme set out in May 2022 by the European Commission aims at ensuring that EU climate and environmental laws are effectively implemented. The European Climate Law translates the European Green Deal net zero target into legislation, requiring Europe’s economy and society to be climate-neutral by 2050. In addition, in February 2021 the European Commission outlined the EU Strategy on Adaptation to Climate Change as a long-term vision for the EU to become a climate resilient society, and to be fully adapted to the unavoidable impacts of climate change by 2050. The actions taken under this strategy may make a crucial contribution to the prevention of the cardiovascular impacts of heat and cold. In addition, climate adaptation is one of the priority themes under the Urban Agenda for the EU, which addresses problems cities are facing by setting up partnerships between the European Commission, EU organisations, national governments, city authorities and other stakeholders such as non-governmental organisations.

Many (16 as of 2020) EEA member countries have national or federal heat-health action plans (Martinez et al., 2022), whereas in some there are subnational and local plans for preventing health impacts from heat (Vanderplanken et al., 2021). Heat-health action plans are proven to be effective (WHO, 2021). Preventing heat impacts on cardiovascular health is a common priority area of national climate change adaptation policies in the EEA’s 38 member and collaborating countries, listed in a recent report as the 3rd most frequent (ECHO, 2022).

On cold, many EEA member countries have policies to tackle wintertime energy poverty, while the EU committed to protecting vulnerable consumers and made energy poverty a policy priority in the 2019 ‘Clean energy for all Europeans’ package. The package also introduced the instrument of national energy and climate plans (NECPs), whereby all EU countries outline 10-year national plans to address the different energy and climate targets. This includes requirements to measure energy poverty and to tackle it wherever it is identified. The European Green Deal also stresses the need to integrate the goal of mitigating energy poverty and supporting a just energy transition for all. The Renovation wave strategy, presented in 2020, has tackling energy poverty and the worst performing buildings amongst its three focus areas for action. Specific regulation is envisioned in the European Commission’s legislative proposals to revise the Energy Performance of Buildings Directive and the broader Energy Efficiency Directive. 

In October 2021, the European Commission published a toolbox of measures proposing actions that EU countries can take to tackle rising energy prices and protect consumers and businesses. Some of these include measures to reduce energy costs for all energy end-users and to avoid disconnections from the energy grid, as well as state aid to companies or industries to weather the crisis.