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Effects of Heat on Human Health

These slides were generously donated to the SOPHEA project by

Nathalie Nidens, MD, Msc

2022

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�� https://creativecommons.org/share-your-work/cclicenses/�

You may use these slides under the following Creative Commons license:

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Climate changes causes more frequent, intense and longer heat waves

For Germany:
1971-2000: Ø 4.6 hot days per year
By 2050: Ø 15 hot days per year
By 2100: Ø 40 hot days per year

Hot day:

Temperature >30° C

Heat wave:�No consistent international definition

Heat Wave Characteristics in the United States by Decade, 1961–2021

Source: EPA United States Environmental Protection Agency https://www.epa.gov/climate-indicators/climate-change-indicators-heat-waves

Heat is one of the biggest climate change-related threats to human health today. But what do we mean when we speak about heat?

There is no single definition for „heat wave“ within the international community. Therefore, when comparing statistics and studies it is important to check for definitions.
Often, a heat wave is defined by a certain number of subsequent days that cross a certain temperature threshold. In Germany, the German Weather Service defines a hot day as a day that reaches at least 30 °C. In this context, a heatwave is often defined as a time period with at least three subsequent hot days.

Climate change increases the probability of more frequent, longer and more intense heat waves. As seen in the US (graph on the left), compared to the 1960s, heat waves are occurring more often and are longer and hotter on average in the 2020s. Additionally, the length of the annual heat wave season has increased.

Projections for Germany predict a multifold increase in hot days by the middle and end of this century, if we continue business as usual.

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Media reports

Source: https://www.imperial.ac.uk/news/236696/climate-change-made-deadly-heatwave-india/

Source: https://globalnews.ca/news/8810459/bc-alberta-2021-heat-dome-research/

Source: https://www.theguardian.com/world/2022/may/02/pakistan-india-heatwaves-water-electricity-shortages

To illustrate the previous point, you can see headlines from newspaper articles and press releases in 2022.

Pakistan and India suffered from an extreme heatwave in April 2022, a heatwave that occured earlier than usual heat events in that region. North-west and central India experienced the hottest April in 122 years. Record temperatures reached up to almost 50 °C. The heatwave had a devastating impact on crops, including wheat and various fruits and vegetables. In India, the yield from wheat crops dropped by up to 50% in some of the areas worst hit by the extreme temperatures. Additionally, India faced its worst electricity shortage in six decades. An analysis carried out by an international team of leading climate scientists led by the Imperial College of London found that the heatwave was about 30 times more likely because of human-caused climate change.

But we see such extreme events not only in regions that are hotter anyhow. In June 2021, Canada experienced a record-breaking heat wave with nearly 50 °C in British Columbia. A study by researchers at universities in the United Kingdom from 2022 shows that this heat wave was among the most extreme ever recorded globally. The study found just five other heat waves since the 1960s were more extreme, based on how far they surpassed average summertime heat over the previous 10 years.

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Vulnerability to heat is increasing

Source: The 2021 report of the Lancet Countdown on health and climate change: code red for a healthy future.�For a full description of the indicator, see the 2021 report of the Lancet Countdown at lancetcountdown.org

Population Vulnerability to Extremes of Heat

Heat vulnerability index by country from 1990-2019

The number of people exposed to extreme heat is growing, as data from the Lancet Countdown on health and climate change shows.

The animation displays the population vulnerabiliy to extreme heat by country from 1990-2019 using a heat vulnerability index. This indicator uses a composite index ranging from 0 to 100, which considers the proportion of the population over 65, the prevalence of chronic diseases (chronic respiratory diseases, cardiovascular diseases, and diabetes), and the proportion of urban population. Higher numbers represent higher vulnerability.

In 2018, 220 million more heatwave exposures affecting vulnerable populations were observed – 11 million more than the previous record set in 2015.
Populations in Europe and the Eastern Mediterranean are among the most vulnerable to the health effects of heat. However, the Western Pacific, South-East Asian and
African Regions have all seen a dramatic increase in vulnerability of >10% since 1990.

Note: There have been new Lancet Countdown reports since this slide was created. Check the Lancet Countdown data explorer for the latest data: https://www.lancetcountdown.org/data-platform/

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Who is at risk?

Elderly people

People with chronic medical conditions

Pregnant women

Infants and children

Athletes

(Outdoor) workers

People who are socially isolated

People with low socio-economic status

People on certain medication

Heat can affect everyone. However, there are certain population groups that are especially at risk for heat-related health issues. Here you can see a number of population groups that are especially vulnerable. Especially vulnerable populations include those over 65 years of age – particularly those with chronic medical conditions, infants and children, pregnant women, outdoor workers, athletes and attendees of outdoor events (e.g. music festivals), and the poor.

This vulnerability can be due to different reasons:
- Physiological reasons regarding thermoregulation (e.g. elderly people, infants and children, pregnant women)
- Medical reasons (e.g. chronic conditions that have an effect on thermoregulation such as cardiovascular disease, diabetes, neurological conditions; certain medications such as diuretics and antihypertensive drugs can also increase sensitivity to heat)
- Increased exposure to heat (e.g. outdoor workers, athletes – these groups also produce more body heat due to physical activity; homeless people – not displayed on slide)
- Socioeconomic reasons that can affect e.g. the adaptation capacity and exposure of an individual (e.g. people living in a poorly isolated home without any financial means to change their situation; socially isolated people who do not have a support system that can take care of them during a heat wave)

You can find more information about vulnerable groups here: https://ghhin.org/heat-and-health/

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Urban heat island effect

Cities are heating faster due to…
Lack of vegetation
Reflectivity
Heat storing materials
Urban canyons
Waste heat

Picture from Pixabay

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How does heat affect the body?

Cardiovascular system

Fluid and electrolyte balance

Other organs

Source: Ebi et al., Hot weather and heat extremes: health risks, Lancet 2021; 398: 698–7 https://doi.org/10.1016/S0140-6736(21)01208-3

The human body responds to heat stress in two primary ways:

Redistributing blood flow towards the skin (vasodilation) to improve heat transfer from muscles to skin and subsequently to the environment,
and secreting sweat onto the skin, which subsequently evaporates and removes body heat.

These physiological heat stress responses are necessary to limit elevations in core temperature. However, the response can have negative consequences as well. The redistribution and increased blood flow to the skin, due to cutaneous vasodilation, increases cardiac demand while decreasing the heart's filling pressure. These responses require the heart to pump harder and faster, increasing the oxygen demand of the heart. For people with pre-existing heart conditions, this response can lead to a mismatch between a high oxygen demand and a compromised oxygen delivery. A sustained mismatch can lead to cardiac ischaemia, infarction, and ultimately, cardiovascular collapse.

Additionally, sweat production can lead to dehydration if the resultant body water deficits are not adequately replenished. Dehydration decreases blood volume that can eventually exacerbate cardiovascular strain and also lead to acute kidney injury and failure. Chronic dehydration can lead to kidney fibrosis and chronic kidney disease.

Under conditions of extreme heat stress, the thermoregulatory capacity of the body can be exceeded, resulting in overheating of the body. High internal temperatures (39–40°C), combined with ischaemia and increased oxidative stress after blood redistribution, can cause cell, tissue, or organ damage, with the brain, heart, kidneys, intestines, liver, and lungs at the greatest risk.

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„Twenty-seven ways a heat wave can kill you“

limited blood flow

damage to cells

inflammatory response

blood clotting

breakdown of muscle tissue

heart

kidneys

lungs

digestive tract

brain

liver

pancreas

A research group carried out a systematic synthesis of deadly heat physiological pathways to make the point that the human body is sensitive to heat and that heat waves can harm anyone (even the young and healthy) in ways that extend beyond cardiovascular diseases.

In total, they identified 5 physiological mechanisms triggered by heat exposure (ie, ischemia, heat cytotoxicity, inflammatory response, disseminated intravascular coagulation, and rhabdomyolysis) and 7 vital organs that can be critically impacted (ie, brain, heart, intestines, kidneys, liver, lungs, and pancreas). Of 35 possible combinations (5 physiological mechanisms times 7 vital organs), we found medical evidence for 27 different pathways by which physiological mechanisms triggered by heat can lead to organ failure and ultimately death.

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How much heat can the body tolerate?

Perceived temperature depends on...
air temperature
relative humidity
wind speed
sun exposure
...
But:

Also dependend on the individual‘s vulnerability!

Source: Prof. Epstein, Israel: Checklist for hikers, https://arielschecklist.com/wbgt-chart/

The scale and nature of the health impacts of heat depend on the timing, intensity and duration of a temperature event, the level of acclimatization, and the adaptability of the local population, infrastructure and institutions to the prevailing climate. The precise threshold at which temperature represents a hazardous condition varies by region, other factors such as humidity and wind, local levels of human acclimatization and preparedness for heat conditions.

In Germany, heat warnings are therefore not only issued based on the actual air temperature but on the perceived temperature which includes some of the factors mentioned above.

On the left you can see a chart for the Wet Bulb Globe Temperature (WBGT). The WBGT is a measure of the heat stress in direct sunlight, which takes into account temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). Depending on the humidity, you can see that the perceived temperature varies from the actual temperature: High humidity increases the perceived temperature. Constellations in black pose a very high risk for heat casualties.

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Heat is deadly…

Source: The 2021 report of the Lancet Countdown on health and climate change: code red for a healthy future.�For a full description of the indicator, see the 2021 report of the Lancet Countdown at lancetcountdown.org

Heat-related mortality in 65+ y/o

Percentage change in the number of heat-related deaths from a 2000-2005 baseline, six-year moving average

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...but death is „only“ the tip of the iceberg

Source: Global Heat Health Information Network https://ghhin.org/in-the-body/

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Spectrum of heat-health outcomes

Source: Leyk D, Hoitz J, Becker C, Glitz KJ, Nestler K, Piekarski C: Health risks and interventions in exertional heat stress. Dtsch Arztebl Int 2019; 116: 537–44. DOI: 10.3238/arztebl.2019.0537

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Spectrum of heat-health outcomes (2)

Source: Own illustration (KLUG e.V.), translated by Nathalie Nidens

In addition to heat illnesses, temperature extremes can also worsen chronic conditions or lead to complications of those conditions including cardiovascular, respiratory, and cerebrovascular disease and diabetes-related conditions.

For example, the risk for heart attacks, strokes and kidney failure is increased during heat waves. People with chronic respiratory diseases such as asthma and chronic-obstructive pulmonary disease (COPD) experience exacerbations of their condition. Overall, heat also worsens mental health and alters behavior: People tend to me more aggressive and prone to violence and crimes during heat waves. The number of suicides rises during heat waves.

More recently, there has been evidence for the effects on pregnancy and births. Heat waves increase the risk for preterm deliveries and adverse birth outcomes such as low birth weight and still births.

Once again, you can see that heat has a myriad of effects on human health.

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HEALTH IMPACTS OF EXPOSURE TO EXTREME HEAT

Increased risk of accidents

Potential disruption of infrastructure

Power
Water
Transport
Productivity

Increased transmission of

Food and waterborne diseases
Marine algal blooms

Impact on health services

Increased ambulance call-outs and slower response times
Increased number of hospital admissions
Storage of medicines

Hospitalization

Respiratory disease
Diabetes mellitus
Renal disease
Stroke
Mental health conditions

Accelerated death from

Respiratory disease
Cardiovascular disease
Other chronic conditions

Heat-related illnesses

Dehydration
Heat cramps
Heat syncope
Heat exhaustion
Heat stroke

INDIRECT IMPACTS

DIRECT IMPACTS

Source: Adapted from https://www.who.int/news-room/fact-sheets/detail/climate-change-heat-and-health

What we have already discussed is the right side of this slide – the direct impacts. However, heat also has important indirect health effects. Heat can alter the transmission of diseases, air quality, and critical social infrastructure such as energy, transport, and water. Heat waves, alone or in combination with e.g. forest fires, can disrupt health services. They have the potential to increase the patient burden on emergency health services, increase demand on ambulatory services, and increase emergency admission and hospitalization. This can also affect health service delivery for “regular” conditions.

Increasing temperatures also mean increased costs for health facilities to provide sufficient cooling and to retrofit health facilities to improve ventilation, cooling, insulation, energy and water resources to function efficiently.

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What can we do?

Long-term development and planning

Preparation before the summer

Prevention during the summer

Specific responses to heat-waves

Source: GAK Recommendations for Heat Action Plans, BMUV 2017, translated by Nathalie Nidens

Considering the effects of heat on human health, it is therefore important to take systematic action as quickly as possible. Health effects of hot weather can be prevented, and public health strategies and measures can be adopted.

In 2008, the WHO Regional Office for Europe published a guidance document on heat-health action plans (HHAP). A structured HHAP is a tool that includes a portfolio of measures that may be taken before and during the summer in preparation for and during heat-waves. Implementation of the plan can be seen as being divided into five phases (image on the right):

1. longer-term development and planning;

2. preparation before the summer (pre-summer);

3. prevention during the summer (summer);

4. specific responses to heat-waves;

5. monitoring and evaluation.

HHAPs can be developed for the national, regional and local level. In Europe, various countries already developled and implemented national HHAPs in response to the heat wave of 2003 (e.g. Italy, France, Spain). Other countries such as Germany see the responsibility on the local level and therefore urge municipalities to develop HHAPs.

Confronting the risks of rising temperatures calls for action from all of society. Measures within a HHAP are usually linked to warnings issued by heat–health warning systems (HHWS). HHWS are instruments to prevent negative impacts of the thermal environment on health during heat-waves. They use weather forecasts to predict situations which are associated with an increase in mortality and/or morbidity and issue warnings accordingly. Measures are to be taken not only within regional or local administrations but also within institutions and organizations that care for or can reach vulnerable population such as hospitals, nursing services, childcare services, sports clubs, or workplaces. Ideally, these institutional heat-health concepts intersect with a larger heat-health action plan. In addition to structural prevention, individuals also can adapt their behavior to heat waves (e.g. drinking enough, no excessive exercise during the hottest hour of the day, using sun-screen, staying in the shade etc.) (image on the left).

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Core elements of heat-health action plans

Agreement on a lead body

Accurate and timely alert systems

Heat-related health information plan

Reduction in indoor heat exposure

Particular care for vulnerable population groups

Preparedness of the health and social care system

Long-term urban planning

Real-time surveillance and evaluation

The 2008 Guidance identified eight core elements that are important for successful implementation of HHAP based on literature and existing HHAP. These elements include:

1. agreement on a lead body (to coordinate a multipurpose collaborative mechanism between bodies and institutions and to direct the response if an emergency occurs);
2. accurate and timely alert systems (heat–health warning systems trigger warnings, determine the threshold for action and communicate the risks);
3. a heat-related health information plan (about what is communicated, to whom and when);
4. a reduction in indoor heat exposure (medium- and short-term strategies) (advice on how to keep indoor temperatures low during heat episodes);
5. particular care for vulnerable population groups;
6. preparedness of the health and social care system (staff training and planning, appropriate health care and the physical environment);
7. long-term urban planning (to address building design and energy and transport policies that will ultimately reduce heat exposure);
8. real-time surveillance and evaluation.

These eight elements are not sequential, though some are primarily about planning and others more about response.

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Examples for adaptation measures

Communication strategy:

Acute and timely alert systems
Channels: local and mass media, organized alert cascades (e.g. „heat hotlines“)
Information on risks and individual behavioral measures

Response to acute events:

Providing cooling zones, public drinking fountains
Triggering institutionial heat-health concepts (e.g. in hospitals, care homes, work places...)

Long-term heat resilience:

Urban planning (building design, green spaces, ponds and fountains, external shading…)
Mitigation of climate change

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Reflection points

This presentation focuses on human health. Is the One Health approach applicable to heat waves? If yes, how so?
We live in times of multiple crises and tight budgets. How would you prioritze measures tackling heat waves? How would you address concurrent risks?
This presentation mentiones a guidance document on heat-health action plans from the WHO for the European region. Are heat-health action plans adoptable in resource-limited settings? What challenges might arise and how could those be tackled? What could we learn from resource-limited settings?
Some of the most vulnerable populations are the hardest to reach. How would you design a communication strategy targeting vulnerable populations? What multipliers and messages are essential?

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References

Kahlenborn, Walter et al. Umweltbundesamt (2021). Klimawirkungs- und Risikoanalyse 2021 für Deutschland. Kurzfassung. Climate Change | 26/2021. https://www.umweltbundesamt.de/publikationen/KWRA-Zusammenfassung
WHO Regional Office for Europe (2008). Heat–health action plans: guidance. https://apps.who.int/iris/rest/bitstreams/1351849/retrieve
WHO Regional Office for Europe. (‎2021)‎. Heat and health in the WHO European Region: updated evidence for effective prevention. https://apps.who.int/iris/handle/10665/339462
Romanello, Marina et al. “The 2021 report of the Lancet Countdown on health and climate change: code red for a healthy future.” Lancet (London, England) vol. 398,10311 (2021): 1619-1662. doi:10.1016/S0140-6736(21)01787-6
Mora, Camilo et al. ‘’Twenty-Seven Ways a Heat Wave Can Kill You: Deadly Heat in the Era of Climate Change”. Circulation. Cardiovascular quality and outcomes vol. 10,11 (2017): e004233. doi:10.1161/CIRCOUTCOMES.117.004233
Global Heat Health Information Network: https://ghhin.org/understanding-heat/
Global Heat Health Information Network: https://ghhin.org/heat-and-health/

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Questions or Comments?

Thank you for your attention !